Cryo-con 24C User Manual

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User's Guide

Model 24C

Cryogenic Temperature Controller

CRYOGENIC CONTROL SYSTEMS, INC.

P.O. Box 7012 Rancho Santa Fe, CA 92067 Tel: (858) 756-3900 Fax: (858) 759-3515 www.cryocon.com

Printing History

Edition 3e.

Certification

Cryogenic Control Systems, Inc. (Cryo-con) certifies that this product met its published specifications at the time of shipment. Cryo-con further certifies that its calibration measurements are traceable to the United States National Institute of Standards and Technology (NIST).

Warranty

This product is warranted against defects in materials and workmanship for a period of one year from date of shipment. During this period Cryo-con will, at its option, either repair or replace products which prove to be defective.

For products returned to Cryo-con for warranty service, the Buyer shall prepay shipping charges and Cryo-con shall pay shipping charges to return the product to the Buyer.

However, the Buyer shall pay all shipping charges, duties, and taxes for products returned to Cryo-con from another country.

Warranty Service

For warranty service or repair, this product must be returned to a service facility designated by Cryo-con.

Limitation of Warranty

The foregoing warranty shall not apply to defects resulting from improper or inadequate maintenance by the Buyer, Buyer supplied products or interfacing, unauthorized modification or misuse, operation outside of the environmental specifications for the product, or improper site preparation or maintenance.

The design and implementation of any circuit on this product is the sole responsibility of the Buyer. Cryo-con does not warrant the Buyer's circuitry or malfunctions of this product that result from the Buyer's circuitry.

In addition Cryo-con does not warrant any damage that occurs as a result of the Buyer's circuit or any defects that result from Buyersupplied products.

Notice

Information contained in this document is subject to change without notice.

Cryo-con makes no warranty of any kind with regard to this material, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose.

Cryo-con shall not be liable for errors contained herein or for incidental or consequential damages in connection with the furnishing, performance, or use of this material. No part of this document may be photocopied, reproduced, electronically transferred, or translated to another language without prior written consent.

Trademark Acknowledgement

CalGen® and Cryo-Con® are registered trademarks of Cryogenic Control Systems, Inc. All other product and company names are trademarks or trade names of their respective companies.

Safety

The Model 24C does not contain any user serviceable parts. Do not open the enclosure. Do not install substitute parts or perform any unauthorized modification to the product. For service or repair, return the product to Cryo-con or an authorized service center.

Cryo-con Model 24C

Table of Contents

Introduction................................................................................................. 1

Sensor Inputs.......................................................................................1

Control Loops....................................................................................... 2

User Interface...................................................................................... 2

Remote Control....................................................................................4

Preparing the controller for use..................................................................7

Supplied Items..................................................................................... 7

Verify the AC Power Line Voltage Selection.........................................7

Apply Power to the Controller...............................................................8

Installation............................................................................................9

Initial Setup and Configuration.............................................................11

A Quick Start Guide to the User Interface...................................................17

Specifications, Features and Functions......................................................21

Specification Summary........................................................................ 21

Performance Summary........................................................................27

Input Channel Characteristics..............................................................30

Control Loop Outputs...........................................................................34

Remote Interfaces................................................................................ 36

Rear Panel...........................................................................................37

Mechanical, Form Factors and Environmental.....................................38

Front Panel Operation................................................................................41

The Keypad.......................................................................................... 41

The Front Panel Display.......................................................................46

Front Panel Menu Operation......................................................................51

Instrument Setup Menus......................................................................51

Basic Setup and Operation.........................................................................73

Configuring a Sensor........................................................................... 73

Using NTC Sensors............................................................................. 74

Using PTC resistor sensors.................................................................76

Downloading a Sensor Calibration Curve.............................................77

Autotuning............................................................................................80

Temperature Ramping.........................................................................85

Cryocooler Signature Subtraction.........................................................88

Using an external power booster..........................................................91

Using CalGen....................................................................................... 91

Using Thermocouple Sensors..............................................................95

System Shielding and Grounding Issues....................................................99

Instrument Calibration................................................................................101

Cryo-con Calibration Services.............................................................. 101

Calibration Interval...............................................................................101

Remote Operation......................................................................................102

Remote Interface Configuration...........................................................102

Remote Programming Guide...................................................................... 105

General Overview................................................................................ 105

An Introduction to the SCPI Language................................................. 106

iii

Cryo-con Model 24C

Remote Command Tree....................................................................... 115

Remote Command Descriptions..........................................................119

Code snippet in C++............................................................................ 138

EU Declaration of Conformity..................................................................... 139

Appendix A: Installed Sensor Curves..........................................................141

Factory Installed Curves.......................................................................141

User Installed Sensor Curves...............................................................142

Sensor Curves on CD..........................................................................143

User Calibration Curve File Format......................................................143

Appendix B: Updating Instrument Firmware...............................................147

Discussion............................................................................................ 147

Updating unit firmware.........................................................................148

Appendix C: Troubleshooting Guide...........................................................151

Error Displays....................................................................................... 151

Control Loop and Heater Problems......................................................152

Temperature Measurement Errors.......................................................153

Remote I/O problems...........................................................................154

General problems................................................................................ 156

Appendix D: Tuning Control Loops.............................................................157

Introduction.......................................................................................... 157

Various methods for obtaining PID coefficients....................................157

Manual Tuning Procedures..................................................................158

Appendix E: Sensor Data...........................................................................159

Cryo-con S700 Silicon Diode................................................................159

Cryo-con S900 Silicon Diode................................................................160

Cryo-con R500 Ruthenium-Oxide Sensor............................................161

Cryo-con R400 Ruthenium-Oxide Sensor............................................162

Sensor Packages.................................................................................163

Appendix F: Configuration Scripts.............................................................. 167

Script File Structure ............................................................................. 167

Script File Example..............................................................................170

Appendix G: Sensor Data Tables................................................................173

Silicon Diode........................................................................................173

Platinum RTD....................................................................................... 175

Rhodium-Iron....................................................................................... 175

Cryogenic Linear Temperature Sensor (CLTS)....................................175

Cernox™..............................................................................................176

Ruthenium-Oxide.................................................................................178

Appendix H: Rear Panel Connections........................................................181

Sensor Connections............................................................................. 181

Control Loop #1 Connections...............................................................183

Control Loop #2 and Relay Connections.............................................183

Ethernet (LAN) Connection..................................................................184

IEEE-488.2 Connections...................................................................... 184

RS-232 Connections............................................................................184

Index........................................................................................................... 185

Cryo-con Model 24C

Index of Figures

Figure 1: 4122-030 Rack Mount Kit............................................................9

Figure 2: 4034-032 Rack Mount Kit............................................................10

Figure 3: Model 24C Rear Panel Layout.................................................... 37

Figure 4: Model 24C Front Panel Layout...................................................41

Figure 5: Thermocouple Module.................................................................95

Figure 6: Thermocouple Switches.............................................................. 95

Figure 7: Proper Assembly of the Input Connector ....................................181

Figure 8: Diode and Resistor Sensor Connections.....................................182

Figure 9: RS-232 Null Modem Cable..........................................................184

Cryo-con Model 24C

Index of Tables

Table 1: Model 24C Instrument Accessories...............................................14

Table 2: Cryogenic Accessories..................................................................15

Table 3: Loop #1 Output Summary.............................................................18

Table 4: Control Type Summary..................................................................19

Table 5: Supported Sensor Types...............................................................21

Table 6: Accuracy and Resolution for PTC Resistors..................................22

Table 7: Minimum and Maximum Resistance vs. Bias Voltage...................23

Table 8: Resolution for NTC Resistors........................................................24

Table 9: 10mV Constant-Voltage Accuracy Specifications..........................24

Table 10: Supported Sensor Configurations...............................................30

Table 11: PTC Resistor Sensor Configuration...........................................31

Table 12: Loop 1 Heater output ranges.......................................................34

Table 13: Loop 2 Heater output ranges.......................................................35

Table 14. AC Power Line Fuses..................................................................38

Table 15: Keypad key functions..................................................................45

Table 16: Temperature Units.......................................................................47

Table 17: Input Channel Configuration Menu..............................................52

Table 18: Control Loop Setup Menus..........................................................55

Table 19: User Configurations Menu..........................................................59

Table 20: System Configuration Menu........................................................ 60

Table 21: Over Temperature Disconnect Configuration..............................62

Table 22: Network Configuration Menu.......................................................64

Table 23: PID Table Edit Menu................................................................... 66

Table 24: Sensor Setup Menu....................................................................67

Table 25: Calibration Curve Menu...............................................................68

Table 26: Auto Tune Menu..........................................................................69

Table 27: digital output Status Indicators....................................................71

Table 28: Digital Output Modes...................................................................71

Table 29: Recommended Sensor Configuration Data.................................78

Table 30: Autotune Menu............................................................................ 83

Table 31: Autotune States...........................................................................84

Table 32: First CalGen Menu, Diode Sensor..............................................92

Table 33: CalGen Menu, 2-point Diode Sensor...........................................93

Table 34: CalGen New Curve Menu...........................................................94

Table 35: Thermocouple Polarities.............................................................97

Table 36: GPIB Host Setup Parameters.....................................................103

Table 37: BB Package Specifications.........................................................164

Table 38: Input Connector Pin-out..............................................................181

Table 39: Sensor Cable Color Codes.........................................................182

Table 40: Loop 1 Connections....................................................................183

Table 41: Loop #2 and Digital Output Connections....................................183

Table 42: RS-232 DB-9 Connector Pinout.................................................184

Cryo-con Model 24C Introduction

Introduction

The Model 24C is a four-input, four-control loop cryogenic temperature controller designed for general purpose laboratory and industrial use. Each input is independent and capable of temperature measurement to <100mK with an appropriate temperature sensor. The Model 24C supports virtually any cryogenic temperature sensor produced by any manufacturer.

The four-output control loop circuits feature a primary 50W heater, a secondary heater of 25W and two 10-Volt non-powered outputs. All control modes are supported by all outputs.

The 24C front panel incorporates a large high resolution graphics TFT type Liquid Crystal Display with an exceptionally wide viewing angle. With it's bright white LED back-light, complete instrument status can be seen at a glance, even from across the room.

Sensor Inputs

The Model 24C has four identical input channels, each of which implements a ratiometric AC resistance bridge. This bridge uses separate, balanced circuits to simultaneously measure both the voltage drop across the temperature sensor and the current flowing through it. By measuring current with a higher accuracy than it can be set, precision resistance measurements are obtained, even at low excitation levels.

Negative-Temperature-Coefficient (NTC) resistors are often used as low temperature thermometers, especially at ultra-low temperature. Examples include Rutheniumoxide, Carbon-Glass, Cernox™, Carbon-Ceramic, Germanium and several others. Their resistance and sensitivity increase dramatically at low temperature but their sensitivity is usually poor at warmer temperatures.

The Model 24C provides robust support for NTC resistor sensors by using constantvoltage AC excitation. In the warm region where the sensor has low resistance and low sensitivity, constant-voltage will apply a high excitation current to improve measurement accuracy. At low temperature where the sensor has high sensitivity and high resistance, measurement errors are dominated by sensor self-heating. Constant-voltage excitation reduces this error by reducing power dissipated in the sensor as temperature decreases.

A common source of error at ultra-low temperature is sensor self-heating due to DC offsets in the measurement electronics. The Model 24C resistance bridge measures the actual current flowing through the sensor to actively cancel DC offsets by using a feedback loop to offset it's excitation source.

Ultra-low temperature systems can be negatively affected by coarse steps in excitation current. The Model 24C prevents this by using a step-less, continuously variable excitation source.

Positive Temperature Coefficient (PTC) resistor sensors including Platinum, CLTS and Rhodium-Iron RTDs use the resistance bridge in a constant-current, AC mode. Platinum RTD sensors use a built-in DIN standard calibration curve that has been extended to 14K for cryogenic use. Lower temperature use is possible with custom calibrations.

Cryo-con Model 24C Introduction

Silicon diode sensors are supported over their full temperature range by using the bridge in a DC, constant-current mode.

Thermocouple sensors are supported by using an optional thermocouple module that plugs into any of the Model 24C's input channels. Up to four modules can be connected to a single instrument.

For all sensor types, conversion of a sensor reading into temperature is performed by using a Cubic Spline interpolation algorithm. In addition to providing higher accuracy than conventional linear interpolation, the spline function eliminates discontinuities during temperature ramps or sweeps by ensuring that the first and second derivatives are continuous.

Control Loops

There are four independent control loop outputs:

1. Loop #1 heater output is a linear, low noise RFI filtered current source that

can provide up to 1.0 Ampere into 50 resistive loads. Three full-scale

ranges are available in decade increments down to 500mW full-scale.

2. Loop #2 is a linear heater with two output ranges of 25-Watts and 2.5-Watt

full-scale into a 50 load.

3. Loop #3 and #4 are a non-powered analog voltage output intended to control

an external booster power supply. Output is selectable at 10 or 5 Volts full

scale.

User Interface

The Model 24C’s user interface consists of a large, bright TFT type Liquid Crystal Display and a full 21-key keypad. In this user-friendly interface, all features and functions of the instrument can be accessed via this simple and intuitive menu driven interface.

The Home screen projects four user configurable zones that allow the real-time display of all input channel, control loop and instrument status information. From this screen, accessing any of the instrument's configuration menus requires only the press of a single key. As always, convenient names can be assigned to input

1A:Sample Holder 2B:First Stage

251.445K 123.845K

300.000K 1-Off-Low 100.000K 2-Off-Low C:Second Stage D:Rad Shield

15.445K 4.845K

RO-600 RuOx 10mV R500 RuOx 1.0mV

channels.

Cryo-con Model 24C Introduction

Cryo-con's innovative instrument configuration menus show real-time status information so the user can instantly view the results of any changes made.

On the control loop menu, the controlling source temperature, heater range and power output level can be observed while tuning a loop.

Loop 1A:Sample Holder Set Pt:300.000K Pgain: 6.000 Igain: 60.00S Dgain: 7.500/S Pman: 5.0000% Type: RampT Input: ChA

A: 123.456K Ramp 42% of Mid

Range: MID PID Table index: 2

Htr Load: 50W Next2

An essential feature for debugging system software is the Network Configuration Menu's ability to show remote commands as they

Network Configuration Menu Dev: M24C1234 DHCP Ena: On Msk:255.255.255.0

00:50:C2:6F:40:3C IP: 192.168.0.198 GWy:192.168.0.1

are sent and received to the instrument.

>input a:temp?;units?;name?;sys:time? <0.5321;K;Sample Holder;14:37:25.

Sensor Curves: The Model 24C includes built-in curves that support most

industry standard temperature sensors. Additionally, eight user calibration curves are available for custom or calibrated sensors. Each user curve may have up to 200 entries and are entered from the front panel, or transferred via any of the available remote interfaces.

New calibration curves may be generated using the CalGen feature to fit any existing diode, Platinum or NTC resistor calibration curve at up to three user specified temperature points. This provides an easy and effective method for obtaining higher accuracy temperature measurements without expensive sensor calibrations.

Data logging is performed by continuously recording to an internal 1,365 entry

circular buffer. Data is time stamped so that the actual time of an event can be determined. Non-volatile memory is used so that data will survive a power failure.

Input Channel Statistics: The Model 24C continuously tracks temperature

history independently on each input channel and provides a statistical summary that indicates the channel's minimum, maximum, average and standard deviation. Also shown are the slope and the offset of the best-fit straight line of temperature history data.

Alarms: Visual, remote and audible alarms are independently programmed to

assert, or clear based on high or low temperature condition, or a detected sensor fault. Latched alarms are asserted on an alarm condition and will remain asserted until cleared by the user.

Cryo-con Model 24C Introduction

Relays: The Model 24C has two 10-Ampere dry-contact relays. These can be used

to control a refrigerator system or other external equipment. Each relay can be asserted or cleared based on the temperature reading of a

selected input channel. High and low setpoints may be set from the front panel or a remote interface. Furthermore, the relays can be manually asserted ON or OFF.

Remote Control

Standard Remote Interfaces include Ethernet and RS-232. IEEE-488.2(GPIB) and USB are optional.

The Model 24C connects directly to any Ethernet Local-Area-Network (LAN) to make measurements easily and economically. TCP/IP and UDP data port servers brings fast Ethernet connectivity to all common data acquisition software programs including LabView. An ASCII text based command language identical to those commonly used with GPIB or RS-232 interfaces is implemented. This is the primary way that user software interfaces to the instrument.

Using the Ethernet SMTP protocol, the controller will send e-mail based on selected alarm conditions. E-mail is configured by using the web page interface.

Using the Ethernet HTTP protocol, the instrument’s embedded web server allows the instrument to be viewed and configured from any web browser.

Cryo-con Model 24C Introduction

In order to eliminate ground-loop and noise pickup problems commonly associated with IEEE-488 systems, the Model 24C moves the internal IEEE-488 circuitry to an optional external module that interfaces directly to the electrically isolated and low noise Ethernet interface. This compact module is completely transparent to the IEEE488 system and does not require changes to customer software or LabView drivers.

Remote Command Language: The Model 24C's remote command language

is SCPI compliant according to the IEEE-488.2 specification. SCPI establishes a common language and syntax across various types of instruments. It is easy to learn and easy to read.

The SCPI command language is identical across all Cryo-con products so that the user's investment in system software is always protected.

Command Scripts can be used to completely configure an instrument including

setting custom sensor calibration curves and PID tables. Further, scripts can query and test data. They are commonly used in a manufacturing environment to set a baseline state and test a target product. In the laboratory, scripts can be used to save and restore configurations for various experiments.

XML (Extensible Markup Language) is used for the structure and format of script files. XML can be generated and edited with a standard text editor. Further, it is easy to read and understand.

Firmware updates: Instrument firmware updates may be installed by using the

Ethernet connection. Cryo-con provides firmware updates, on request, via e-mail. They are free of charge and generally include enhancements and new features as well as problem fixes. Send e-mail to cctechsupport@cryocon.com

Ethernet API: An Applications Program Interface (API) package is supplied that

facilitates communication with the instrument using the TCP/IP and UDP protocols. It is supplied as a Microsoft Windows DLL that is easily linked with C, C++ or Basic programs.

Cryo-con Model 24C Preparing the controller for use

Preparing the controller for use

The following steps help you verify that the controller is ready for use.

Supplied Items

Confirm that you have received the following items with your controller. If anything is missing, contact Cryogenic Control Systems, Inc. directly.

 Model 24C Cryogenic Temperature Controller.  This User’s Manual.  Cryo-con software CD.  Input connector kit (4024-016) consisting of four screw-in DIN-6 input

connectors (PN 04-0414).

 Output connector kit (4124-018) consisting of a 10-pin detachable

terminal block (04-0007) and a dual banana plug(04-0433).

 Detachable 120VAC USA Line Cord (04-0310), or universal Euro cord.  Certificate of Calibration.

Verify the AC Power Line Voltage Selection

The AC power line voltage is set to the proper value for your country when the controller is shipped from the factory. Change the voltage setting if it is not correct. The settings are: 100, 120 220, or 240 VAC. For 230 VAC operation, use the 240 VAC setting.

On the rear panel of the instrument, the AC voltage selection is on the power entry module. If the setting is incorrect, please refer to section Fuse Replacement and

Voltage Selection to change it.

Cryo-con Model 24C Preparing the controller for use

Status: Self Test

Apply Power to the Controller

Connect the power cord and turn the controller on by pressing the Power key for a minimum of 2 Seconds. The front panel will show a Power Up display with the model number and firmware revision.

While the Power Up display is shown, the controller is performing a self-test procedure that verifies the proper function of internal data and program memories, remote interfaces and input/output channels. If an error is detected during this process, the controller will freeze operation with an error message display. In this case, turn the unit off and refer to Appendix C: Troubleshooting Guide.

Caution: Do not remove the instrument’s cover or attempt to repair the controller. There are no user serviceable parts, jumpers or switches inside the unit. Further, there are no software ROM chips, trim pots, batteries or battery-backed memories. All firmware installation and instrument calibration functions are performed externally via the remote interfaces.

Cryogenic Control Systems, Inc. Model 24C SN:209999 Rev: 1.23B IP:192.168.1.5 Static Port: 5000 MAC: 00:50:c2:6f:40:3E Calibration: Testing NVRAM: Testing Device Name: NewCryocon Connecting GPIB Adrs: 012 RS232: 9600

After about fifteen seconds, the self-test will complete and the controller will begin normal operation.

Cryo-con Model 24C Preparing the controller for use

Installation

General

The Model 24C can be used as a bench top instrument, or mounted in an equipment rack. In either case, it is important to ensure that adequate ventilation is provided.

Cooling airflow enters through the side holes and exhausts out the fan on the rear panel. It is important to allow at least ½" of clearance on the left and right sides and to ensure that the exhaust path of the fan is not blocked.

Rack Mounting

You can rack mount the controller in a standard 19-inch rack cabinet using the optional rack mount kit. Instructions and mounting hardware are included with the kit.

4122-030 Single instrument 2U rack mount kit.

4034-032 Single instrument shelf rack mount kit.

4034-031 Dual instrument shelf rack mount kit.

Figure 1: 4122-030 Rack Mount Kit

Cryo-con Model 24C Preparing the controller for use

Using the one- or two-instrument shelf rack mount kit, additional equipment may be mounted on the shelf space next to the controller. Note that these rack mount kits extends the height of the controller from 2U (3½") to 3U (5¼"). Since the controller is an industry standard size, it is possible to mount any similar size instrument next to it in the rack.

Figure 2: 4034-032 Rack Mount Kit

Warning: When using the shelf type rack mount kits, do not use screws that protrude into the bottom of instrument more than ¼". Otherwise, they can touch internal circuitry and damage it.

Cryo-con Model 24C Preparing the controller for use

Initial Setup and Configuration

Before attempting to control temperature, the following instrument parameters should be checked:

1. The Loop #1Heater resistance setting should match the actual heater resistance that you are going to use. Choices are 50 and 25. A heater resistance of less than 25 should use the 25 setting. Using the 50 setting with a heater resistance much less than 50 may cause the instrument to overheat and disengage the control loops.

Set the heater resistance by pressing the Loop 1 key and refer to the Loop

Configuration Menu section.

2. The Loop #1 heater range should be set to a range where the maximum output power will not damage the equipment. To set this parameter, press the Loop 1 key and refer to the Loop Configuration Menu section.

3. The controller has an over-temperature disconnect feature that monitors a selected input and will disconnect both control loops if the specified temperature is exceeded. This feature should be enabled in order to protect your equipment from being over heated. To enable, press the System key and refer to the System Functions Menu section.

i NOTE: Factory defaults may be restored at any time by use of the following sequence: 1) Turn AC power OFF. 2) Press and hold the Enter key while turning power back ON. This sequence will restore factory defaults including resetting user supplied sensor calibration curves and saved user configurations. However, it will NOT erase the instrument’s internal calibration data.

Cryo-con Model 24C Preparing the controller for use

Model Identification

The model number of all Cryo-con controllers is identified on the front and rear panel of the instrument as well as in various instrument displays.

Ordering Information

Standard Description

Model 24C

Controller with four standard multi-function sensor input channels.

Controller includes: User's Manual, Cryo-con software CD, four input connectors, heater connector, terminal block plug, detachable power cord and a certificate of calibration.

Specify AC Line Voltage when ordering:

-100 Configured for 90 - 100VAC with detachable USA power cord.

-110 Configured for 110 - 120VAC with detachable USA power cord.

-220 Configured for 220VAC with detachable universal Euro (Shuko) line cord.

-240 Configured for 240VAC with detachable universal Euro (Shuko) line cord.

Options Description

4039-004

4001-002

4001-001

Thermocouple Input Module. Field installable. Supports all thermocouple types. Controller supports up to 4 modules.

IEEE-488.2 (GPIB) Option. Field installable.

USB Option. Serial Port Emulation. Field installable.

Cryo-con Model 24C Preparing the controller for use

Technical Assistance

Troubleshooting guides and user’s manuals are available on our web page at http://www.cryocon.com. Technical assistance may be also be obtained by contacting Cryo-con as follows:

Cryogenic Control Systems, Inc. PO Box 7012 Rancho Santa Fe, CA 92067-7012

Telephone: (858) 756-3900x100 FAX: (858) 759-3515 e-mail: cctechsupport@cryocon.com

For updates to LabView™ drivers, Cryo-con utility software and product documentation, go to our web site and select the Download area.

Current Firmware Revision Level

As of July, 2014 the firmware revision level for the Model 24C series is 2.52. Instrument firmware can be updated in the field via the LAN port. Updates are available on the Internet.

Current Hardware Revision Level

As of July, 2014, the hardware revision level for the Model 24C

Hardware

Revision

Relay contact rating

Non-powered outputs

Loop 2 output

A B, C

2.0A, 30W 10.0A, 150W

10.0V

10W or 1.0W-

Volt full-scale

Selectable 10V or 5V

full scale.

25W or 2.5W-Volt full-

scale

series is C.

Returning Equipment

If an instrument must be returned to Cryo-con for repair or recalibration, a Return Material Authorization (RMA) number must first be obtained from the factory. This may be done by Telephone, FAX or e-mail.

When requesting an RMA, please provide the following information:

1. Instrument model and serial number.

2. User contact information.

3. Return shipping address.

4. If the return is for service, please provide a description of the malfunction.

If possible, the original packing material should be retained for reshipment. If not available, consult factory for packing assistance.

Cryo-con’s shipping address is:

Cryogenic Control Systems, Inc. 17279 La Brisa Rancho Santa Fe, CA 92067-7012

Cryo-con Model 24C Preparing the controller for use

Instrument Accessories

Cryo-con Part # Description

4034-031

4034-032 One instrument shelf rack mount kit

4034-035

04-0310

04-0317 AC Power Cord, Cont. European (Shuko)

04-0414

04-0007 Ten-pin detachable terminal block for Loop 2 and relay connections.

04-0433

4042-040 8' Sensor cable, four wire, wired to DIN-6 connector.

3124-029

Two instrument shelf rack mount kit

Shielded IEEE-488.2 Interface Bus Cable, 6'6"

AC Power Cord

Din-6 Sensor Input Connector, Amphenol T3400 001

Dual banana plug for Loop 1 connection.

Additional User’s Manual/CD

Table 1: Model 24C Instrument Accessories

Cryo-con Model 24C Preparing the controller for use

Cryogenic Accessories

Cryo-con Part # Description

S900

S900 series Silicon diode Temperature Sensors. Temperature range: 1.4 to 500K

Cryo-con R400 Ruthenium-Oxide temperature sensor.

R400

Temperature range: 2.0K to 273K. Optimized for use in Liquid Helium systems including superconducting magnets.

R500

Cryo-con R500 Ultra-low temperature Ruthenium-Oxide temperature sensor. Temperature range: <100mK to 40K.

CP-100

GP-100

XP-100

XP-1K

3039-002

3039-001

4039-011

4039-012

3039-006

CP-100 series Ceramic Wound RTD, 100

GP-100 series Glass Wound RTD, 100

XP-100 series Thin Film Platinum RTD, 100

XP-1K series Thin Film Platinum RTD, 1,000

Cartridge Heater, Silicon free, 25 / 25 Watt, 1/4" x 1 1/8". Temperature range to 1,600K

Cartridge Heater, Silicon free, 50 / 50 Watt, 1/4" x 1 1/8. Temperature range to 1,600K

Pre-cut Nichrome wire heater w/connectors, 25

Pre-cut Nichrome wire heater w/connectors, 50

Bulk Nichrome Heater Wire, 32AWG, Polyamide insulation, 100’

Table 2: Cryogenic Accessories

Cryo-con Model 24C A Quick Start Guide to the User Interface.

A Quick Start Guide to the User Interface.

Pressing the Power key will toggle the controller's AC power on and off. This key must be pressed and held for two seconds before power will toggle.

Pressing the Stop key will immediately disengage both control loops. Pressing the Control key will engage them.

Use the ESC key to exit an erroneous entry.

Home Status Display

Pressing the Home key will return the screen to the Home Display from anywhere in the sub-menus. The Home Display is the primary display for instrument status information.

The Home Status display consists of four zone quadrants. Each zone has 4 lines, containing 20 characters each, and can be individually configured to show useful information with minimum clutter.

To configure zone displays, press the Display key.

Accessing the heater setpoint

To instantly access the setpoint for either control loop, press the Set Pt key.

Configuring a temperature sensor

Configuring an input sensor from the front panel is performed by using the Input Channel Configuration Menu. First, press input channel key ChA , ChB , ChC , or ChD to select the desired channel for configuration.

The first line of the Input Channel Configuration menu is used to change the sensor units. It shows the selected input channel, the current temperature (in real time) and the current units. An example is shown here.

To change the sensor units, use the + and 0 keys to scroll through the available options. When the desired units are shown, press the Enter key to make the selection. The display will now show the current temperature with the new units.

Next, go to the sensor selection field by pressing the down arrow navigation key. This field is used to select the actual sensor type. In the example shown below, the input channel is currently configured for a standard Cryo-con S900 diode sensor. Use the + and 0 keys to scroll through the available sensors including user sensors. When the desired sensor is shown, press the Enter key to make the selection. A complete listing of selectable sensors is given in Appendix A.

Before one of the user-supplied sensors can be used, the sensor’s calibration curve and configuration data must be installed. This is best done by using Cryo-con’s utility software.

This completes the process of configuring an input channel. Press the Home key to return to the Home Status display.

+ --

+Sen: 1 Cryocon S900

Cryo-con Model 24C A Quick Start Guide to the User Interface.

+

Configuring the Control Loops

Before using the Loop #1 (main heater) control output, it is essential that the proper load resistance and output range be selected. This is done using the Control Loop Setup menu as follows:

 Press the Loop 1 key.  In the Control Loop Configuration menu, Use the up, down, right and left

keys to scroll to the Htr Resistance field. An example is shown here:

 Use the + and 0 keys to select between a 50-

Ohm and a 25-Ohm heater and then press the Enter key.

 Use the navigation keys to scroll to the Range

+

field and then select the desired heater range. Be sure to select a range that does not exceed the ratings of your cryostat. A summary of full-scale output power for the various ranges is given here:

Range

Mid

Low

Max. Output Power

25 50

25 Watts 50 Watts

2.5 Watts 5.0 Watts

0.25 Watts 0.50 Watts

Table 3: Loop #1 Output Summary

Next, the control type should be set by scrolling to the Type field and selecting the desired loop operating mode.

+

Cryo-con Model 24C A Quick Start Guide to the User Interface.

A summary of control types is given here:

Type Description

Off

Control loop is disabled.

Manual control mode. Here, a constant heater output power is

Man

applied. The Pman field selects the output power as a percentage of full-scale.

Table

PID

RampP

RampT

PID control mode where the PID coefficients are generated from a stored, user supplied PID table.

Standard PID control.

Temperature ramp control. Uses PID control to perform a temperature ramp.

Temperature ramp control using a PID table. Uses PID control to perform a temperature ramp.

Table 4: Control Type Summary

Caution: The Model 24C has an automatic control-on-power-up

feature. If enabled, the controller will automatically begin controlling temperature whenever AC power is applied. For a complete description of this function, please see the Auto Ctl function in the

System Functions menu section.

Restoring Factory Defaults

Factory default settings may be restored with the following simple procedure:

1. Turn AC power OFF by pressing the Power key.

2. Press and hold the Enter key while turning AC power back ON. Keep the

key pressed until you see the power-up display indicating that defaults have been restored.

Cryo-con Model 24C Specifications, Features and Functions

Specifications, Features and Functions

Specification Summary

User Interface

Display Type: 40 character by 8 line TFT LCD with LED backlight. Number of Inputs Displayed: Four. Keypad: Sealed Silicon Rubber. Temperature Display: Six significant digits, autoranged. Display Update Rate: 0.5 Seconds. Display Units: K, C, F or native sensor units. Display Resolution: User selectable to seven significant digits.

Input Channels

There are four input channels, each of which may be independently configured for any of the supported sensor types.

Sensor Connection: 4-wire differential. Screw-in type DIN-6 circular.

Connections are described in the Sensor Connections section.

Supported Sensors Include:

Type Excitation

Silicon diode

Platinum RTD

Cernox™ Constant-Voltage AC 100mK to 420K Lakeshore, all types

Ruthenium-Oxide

Carbon-Ceramic

Rhodium-Iron Constant-Current, 1mA AC 1.4 to 800K Oxford PHZ 0002

Germanium Thermistor Silicon Thermistor

Thermistor

CLTS Constant-current, 100uA AC 4 to 325K Vishay CLTS-2B

Thermocouple

Constant-Current, 1mA AC 14 to 1200K

10mA DC

Constant-Voltage AC 100mK to 273K SI RO-600, SI RO-105

Constant-Voltage AC 1.0K to 300K TMi-A1

Constant-Voltage AC 100mK to 100K AdSem, Inc.

Constant-Voltage AC 1.0K to 400K AdSem, Inc.

Constant-Voltage AC 193 - 523K Measurement Specialties

None 1.4 to 1500K All thermocouple type

Temperature

Range

1.4 to 475K

Example

Cryo-con S900 SI-440, 430, 410 Lakeshore DT-670, 470

Cryo-con CP-100 Cryo-con GP-100 Cryo-con XP-100 Cryo-con XP-1K

Table 5: Supported Sensor Types

Cryo-con Model 24C Specifications, Features and Functions

Sensor Selection: Front Panel or remote interface. There are no internal

jumpers or switches.

Sample Rate: 15Hz per channel in all measurement modes.

Digital Resolution: 24 bits.

Measurement Filter: 0.5, 1, 2, 4, 8, 16, 32 and 64 Seconds. Calibration Curves: Built-in curves for industry standard sensors plus eight

user curves with up to 200 entries each. Interpolation is performed using a Cubic Spline.

CalGen: Calibration curve generator fits any diode or resistor sensor curve at

1, 2 or 3 user specified temperature points.

Sensor Performance Specifications:

Diode Sensors

Configuration: Constant-Current mode, 10mA ± 0.05% DC excitation.

Note: Current source error has negligible effect on measurement accuracy.

Input voltage range: 0 to 2.00VDC. Accuracy: ±(80mV + 0.005% * reading) Resolution: 2.3mV Drift: 25ppm/ºC over an ambient temperature range of 25ºC± 5ºC.

PTC Resistor Sensors

Configuration: Constant-Current AC resistance bridge mode.

Ratiometric measurement cancels any error in excitation current.

Drift: 20ppm/ºC over an ambient temperature range of 25ºC± 5ºC. AC Excitation Frequency: 7.5Hz bipolar square wave.

Range

PTC100

1mA

PTC1K

100mA

Max/Min

Resistance

500W

0.01W

7.5KW

0.1W

Table 6: Accuracy and Resolution for PTC Resistors

Excitation

Current

1.0mA

100mA 1.0mW

Resolution Accuracy

0.1mW

± (0.004 + 0.01%)Ω

± (0.05 + 0.02%)Ω

Note: The Model 24C is calibrated with AC excitation. User selection of DC excitation will introduce offset errors in temperature measurement.

Cryo-con Model 24C Specifications, Features and Functions

Thermocouple Sensors

Thermocouple devices are supported by using an optional external module.

Measurement Drift: 25ppm/ºC Input Range: ±70mV Accuracy: ±1.0µ V ± 0.05%. Resolution: 0.0003%

Installed Types: K, E, T and Chromel-AuFe (0.07%). Input Connector: Isothermal, Screw-type terminals.

NTC Resistor Sensors

Type: Constant-Voltage AC resistance bridge with excitations

of 10mV, 3.0mV, 1.0mV and 300µV RMS. Fixed or auto-ranged.

Excitation Current: 2.5mA to 10nA.

Four ranges of 2.5mA, 250uA and 25uA full-scale.

Excitation Frequency: 7.5Hz bipolar square wave. Drift: >10W and <10KW: 15ppm/ºC

<10W or >10KW: 25ppm/ºC

over an ambient temperature range of 25ºC± 5ºC.

DC Offset Current: <8nA by active cancellation. Resistance Range: 0.5W to 1.0MW.

Resistance 10mV 3.0mV 1.0mV 300µV

Maximum

Minimum

Table 7: Minimum and Maximum Resistance vs. Bias Voltage

1.0MW 100KW 100KW 33KW

1W 0.5W 0.5W 0.16W

Cryo-con Model 24C Specifications, Features and Functions

Resolution: Shown below are typical RMS resistance noise values measured at 50% of full-scale on a room-temperature resistor with a 3-Second analog time-constant.

Range 10mV 3.0mV 1.0mV

40W

400W

4KW

40KW

Table 8: Resolution for NTC Resistors

1.0mA 255µW

100μA

2.6mW

10μA

26mW

1.0μA

250mW

1.0mA 255µW

100μA

2.6mW

10μA

26mW

1.0μA

250mW

100μA

2.6mW

10μA

26mW

1.0μA

260mW

1.0μA

2.5W

Accuracy: Accuracy for the 10mV bias setting is specified in ranges according to the following table. The formulas apply from the maximum to the minimum resistance shown below.

Resistance

Range

1Ω

4Ω

40Ω

400Ω

4KΩ

100KΩ

Excitation

Current

Range

1.0mA 1 - 4Ω ±0.02Ω ± 0.05% * Rdg

1.0mA 4 - 40Ω ±0.02Ω ± 0.05% * Rdg

100µA 40 - 400Ω ±0.2Ω ± 0.05% * Rdg

10µA 400 - 4KΩ ±2.0Ω ± 0.05% * Rdg

10µA 4K - 40KΩ ±20Ω ± 0.05% * Rdg

10µA 40K - 100KΩ ±50Ω ± 0.1% * Rdg

Min/Max

Resistance

Accuracy at 25C

Table 9: 10mV Constant-Voltage Accuracy Specifications

While it is possible to measure resistance above100KΩ, accuracy is not guaranteed.

The 1.0mV and lower bias settings are provided for use in very low temperature applications (<~1K) where errors are often dominated by sensor self heating rather than the accuracy of resistance measurement. In the

1.0mV range, the Model 24C will have an accuracy of ± 0.5% over the resistance range of 40 to 10.0KΩ.

Cryo-con Model 24C Specifications, Features and Functions

Control Outputs

Number of Loops: Four. Control Input: Either sensor input. Loop Update Rate: 15Hz per loop. Control Type: PID table, PID, Ramp or Manual. Autotune: Minimum bandwidth PID loop design. PID Tables: Six user PID tables available for storage of Setpoint vs. PID and

heater range. Up to 16 entries/table.

Setpoint Accuracy: Six+ significant digits. Fault Monitors: Control loops are disconnected upon detection of a control

sensor fault or excessive internal temperature. Over Temperature Disconnect: Heater may be relay disconnected from user equipment when a specified temperature is exceeded on any selected input.

Loop #1 Primary Heater Output

Type: Short circuit protected linear current source. Maximum compliance is selectable at 25V or 50V. Ranges: Three output ranges of 1.0A, 0.33A and 0.10A full-scale, which correspond to 50W, 5.0W and 0.5W when used with a 50 load.

Load Resistance: 25 or 50 for maximum output. Minimum Load: 10 in 25 setting, 40 in 50 setting. Digital Resolution: 1.0PPM of full-scale, corresponding to 20 bits. Readback: Heater output power, Heatsink temperature. Connector: Dual Banana-plug.

Loop #2 Heater Output

Type: Short circuit protected linear current source. Compliance is 36V. Ranges: 25W or 2.5W full-scale into a 50 load. Load Resistance: 50 for maximum output. Digital Resolution: 1.0PPM of full-scale, corresponding to 20 bits. Readback: Heater output power. Connector: 10-pin detachable terminal block.

Status Outputs

Audible and Visual Alarms: Independent audible and visual alarms. Status reported via Remote Interface: Heater over temperature fault.

Loop #3 and #4 Outputs

Type: 0 - 10 or 0 - 5 Volt analog output. All control modes available. Maximum Output Current: 20mA. Connector: 10-pin detachable terminal block.

Cryo-con Model 24C Specifications, Features and Functions

Relay Outputs

Number: 2 Type: Dry-contact. Contact Rating: 10A @125 VAC, 5A @250 VAC or 5A @30 VDC for

resistive loads.

Function: Asserted or cleared based on temperature setpoint data. Deadband: User defined. Connector: 10-pin detachable terminal block.

Remote Interfaces

Remote interfaces are electrically isolated to prevent ground loops.

Ethernet: Supported protocols include: HTTP, TCP/IP, UDP and SMTP.

Electrically isolated.

RS-232: Serial port is an RS-232 standard null modem. Rates are 9600,

19,200, 38,400, 557,600 and 115,200 Baud.

IEEE-488 (GPIB): External option. Full IEEE-488.2 compliant.

USB 2.0: External option. Serial port emulator.

Language: Remote interface language is IEEE-488.2 SCPI compliant.

Further, it is identical within the entire Cryo-con instrument line.

Compatibility:

National Instruments LabView™ drivers available for all interfaces.

Ethernet API available for C++ and Basic.

User Setups

Four User Setups are available that save and restore the complete configuration of the instrument.

General



Ambient Temperature: 25

C  5 oC for specified accuracy. Mechanical: 8.5"W x 3.5"H x 12"D. One half-width 2U rack. Instrument bail standard, rack mount kit optional.

Weight: 9 Lbs. Enclosure: Aluminum. Machined Aluminum front panel. Power Requirement: 100, 120, 220 or 240VAC +5% -10%.

50 or 60Hz, 150VA max.

Cryo-con Model 24C Specifications, Features and Functions

MAT

MAV

0.002604

MAV 60 10





5 10





1.36317



M A T

MA V

SenSen

MAV 60 10





5 10





SenRdg



Performance Summary

Measurement Accuracy

Diode Sensors

The formulas for computing measurement accuracy while using diode sensors are:

Where:

MAV is the electronic Measurement Accuracy in Volts MAT is the Measurement Accuracy in Kelvin SenRdg is the sensor reading in Volts at the desired temperature. SenSen is the sensor sensitivity in Volts / Kelvin at the desired temperature.

For example, to calculate the measurement accuracy of the Model 24C using a Cryocon S900 sensor at 10K, look up the sensor reading and sensitivity in the S900 data table in Appendix G. At 10K, SenRdg is 1.36317 Volts and SenSen is 0.002604 Volts/Kelvin . Therefore,

and

The result is MAV = 128V and MAT = 49mK.

Cryo-con Model 24C Specifications, Features and Functions

MA T

MA R

SenSen

MA T

M A R

SenSen

M A R 5.0 10





SenVal5.0 10





Range



M A R 0.002 1.0 10





SenVal



PTC Resistor Sensors (RTDs)

The formulas for PTC resistor sensor in the PTC100 range are:

Where:

MAR is the electronic Measurement Accuracy in Ohms MAT is the Measurement Accuracy in Kelvin SenVal is the sensor reading in Ohms at the desired temperature. SenSen is the sensor sensitivity in Ohms / Kelvin at the desired temperature.

To calculate the measurement accuracy of the Model 24C using a 100W Platinum RTD in the PTC100 range with the sensor at 77.35K, look up the sensor reading and sensitivity in Appendix G. The appendix shows that SenRdg is 20.38W and SenSen is

0.423 W/Kelvin. Therefore, the computed values show that MAR = 0.004038W and MAT = 9.5mK.

For ranges other than PTC100, please refer to the PTC Specifications table.

NTC Resistor Sensors

The formulas for NTC resistor sensors are: Where:

MAR is the electronic Measurement Accuracy in Ohms Range is the resistance range in Ohms (100, 1K or 10K) MAT is the Measurement Accuracy in Kelvin SenVal is the sensor reading in Ohms at the desired temperature. SenSen is the sensor sensitivity in Ohms / Kelvin at the desired temperature.

To calculate the measurement accuracy of the Model 24C using a Cryo-con R500 Ruthenium-Oxide sensor in the 1KW range with the sensor at 1.0K, look up the sensor reading and sensitivity in Appendix G. SenVal is 2327W and SenSen is

-1203W/Kelvin. Therefore the computed values equal MAR = 0.17W and MAT = 100K.

Cryo-con Model 24C Specifications, Features and Functions

MRT

SenSen

MR FullScale 2





Measurement Resolution and Control Stability

The input analog-to-digital converter used by the Model 24C is 24 bits with no missing codes. Thus, the measurement resolution is identifiable as one part in 2

-24

. However, the only use for measurement resolution is to compute control stability. Since control stability is limited by the output DAC rather than the input, the measurement resolution specification is limited to one part in 2

-20

Where:

MR is the electronic measurement resolution in sensor units. FullScale is the full scale range MRT is the measurement resolution in temperature units. SenSen is the sensor sensitivity at the measurement point.

Cryo-con Model 24C Specifications, Features and Functions

Input Channel Characteristics

There are four independent, multi-purpose input channels; each of which can separately be configured for use with any supported sensor.

Input Configurations

A complete list of the sensor types supported by the Model 24C is shown below:

Sensor Type

Diode 2.25V CI 10µA DC Silicon diode, GaAs diode.

ACR

PTC100

PTC1K

CLTS

TC70 ±70mV None 0

None 0 None 0 Disable Input Channel

Max. Voltage/

Resistance

10 to 1.0M

0.5 - 500

5 - 5.0K

300

Bias types are:

CI – Bridge maintains a constant current through the sensor. CV – Bridge maintains a constant voltage-drop across the sensor.

Bias Type

CI 1.0mA AC

CI 100uA AC

CI 100uA AC CLTS

Table 10: Supported Sensor Configurations

Excitation

Current

2.5mA - 10nA ACNTC resistors including Ruthenium Oxide, Cernox™

100 Platinum, Rhodium-Iron

1,000 Platinum

All thermocouple types. (requires Thermocouple option)

Typical Use

i Note: Any disconnected inputs to the Model 24C should be set to type 'None'. This will turn the input off.

Silicon Diode Sensors

Silicon diode sensors (2-volt diodes) are configured with a 10mA current source excitation and a 2.25 Volt input voltage range.

Gallium-Arsenide Diode Sensors

Gallium-Arsenide diodes or 6-Volt diodes are sometimes used in systems where magnetic fields are present. Use is limited to operation above about 30K with fields of less than 5T. The Model 24C supports these sensors down to 25K. If your requirements are for lower temperature operation, Ruthenium-Oxide is a better choice.

Gallium-Arsenide sensors do not fit standard calibration curves, therefore, the user must provide a sensor-specific curve before using this type of sensor.

Cryo-con Model 24C Specifications, Features and Functions

Cryogenic Linear Temperature Sensor (CLTS)

Supported by use of a 100uA constant-current AC resistance bridge. A standard calibration curve for the Vishay CLTS-2B sensor is available on the utility CD. Maximum resistance is 1.2K and minimum is 10. Sensor type is PTC1K.

PTC Resistor Sensor (RTDs)

The Model 24C supports all types of Positive-Temperature-Coefficient (PTC) resistive sensors using a constant-current AC or DC resistance bridge technique.

Standard calibration curves are provided for DIN43760 and IEC751 Platinum sensors. These curves have been extended down to 14K. Below that, the sensors can be used with user supplied calibration curves.

A table of recommended setups for various types of PTC resistor sensors is shown here:

Type Measurement Range Sensor Excitation

Platinum, 100 1.0K - 0.01

Platinum, 1000 10K - 0.1 100mA, AC

Rhodium-Iron

Table 11: PTC Resistor Sensor Configuration

1.0K - 0.01

1.0mA, AC

When AC excitation is On, the sensor excitation current is a 10 Hz square wave. This square wave excitation generates a small noise signal in the sensor cable, which can be picked up by sensitive measurement equipment in the system. Turning AC excitation Off will eliminate this noise at the cost of introducing a thermal EMF DC offset voltage into the sensor measurement.

Cryo-con Model 24C Specifications, Features and Functions

sen so r

bi as

P2

NTC Resistor Sensors

The Model 24C supports almost all types of Negative-Temperature-Coefficient (NTC) resistive sensors by using a constant-voltage AC resistance bridge technique, these sensors can be used down to very low temperatures. Examples of NTC resistor sensors include: Ruthenium Oxide, Cernox™, Carbon Glass, Germanium and other thermistors.

Constant-voltage excitation is necessary since the resistance thermometers used below about 10K exhibit a negative temperature coefficient. Therefore, a constantvoltage measurement reduces the power dissipation in the sensor as temperature decreases. By maintaining low power levels, sensor self-heating errors that occur at very low temperatures are minimized.

In the constant-voltage mode, sensor excitation is a 7.5Hz bipolar square-wave. For more information on using the Model 24C with NTC resistor sensors, please refer

to the section titled "Voltage Bias Selection". Power dissipation in the sensor is computed by:

The actual power being dissipated in the sensor may be viewed in real-time by going to the Input Configuration Menu. An asterisk (*) character next to the temperature display indicates that the resistance bridge is not balanced at the proper voltage bias.

When used with high resistances, measurement accuracy steadily degrades due to the extremely low excitation current required. The trade-off in measurement accuracy vs. sensor excitation current is taken for two reasons:

1. The sensitivity of NTC resistor sensors is extremely high in the low temperature end of their range. Therefore the reduced measurement accuracy does not degrade temperature measurement accuracy.

2. The low current settings are required since sensor self-heating at low temperature is a very significant source of errors.

Calibration tables for NTC sensors may be entered either directly in Ohms or in (base

10) Log of Ohms to accommodate the generally logarithmic nature of their calibration curves.

Cryo-con Model 24C Specifications, Features and Functions

CalGen Calibration Curve Generator

The CalGen feature generates new calibration curves for Silicon diode, thermocouple or Platinum sensors. This provides a method for obtaining higher accuracy temperature measurements without expensive sensor calibrations.

Curves can be generated from any user-selected curve and are written to a specified internal user calibration curve area.

The CalGen function may be performed in the instrument by using the front panel. Alternatively, the feature is also implemented in the Cryo-con utilities software.

Input Channel Statistics

Input temperature statistics are continuously maintained on each input channel. This data may be viewed in real time on the Input Channel menu, or accessed via any of the remote I/O ports.

Statistics are:

Minimum Temperature. Maximum Temperature. Temperature Variance. Slope and Offset of the best-fit straight line to temperature history. Accumulation Time

The temperature history may be cleared using a reset command provided.

Electrical Isolation and Input Protection

The input channel measurement circuitry is electrically isolated from other internal circuits. However, the common mode voltage between an input sensor connection and the instrument's ground should not exceed 40V.

Sensor inputs and outputs are provided with protection circuits. The differential voltage between sensor inputs should not exceed 15V.

Cryo-con Model 24C Specifications, Features and Functions

Control Loop Outputs

Control Loop #1, Primary Heater Output

The Loop #1 heater output is a short circuit protected linear current source. This output is heavily regulated and RFI filtered. External filters should not be necessary.

Automatic shutdown circuitry is provided that will protect the heater output stage from excessive temperature. Here, the heater output will be turned off until the output stage returns to its safe operating area, then the output will be returned to normal operation.

Load resistance values of either 25 or 50 may be selected. Using a 25 load, the heater will be automatically configured to have a compliance voltage of 25V. With a 50 load, the compliance voltage is 50V. In either case, the maximum output current is 1.0A.

Range

High

Medium

Low

Compliance Voltage

25 50

25V 50V 1.0A 25 Watts 50 Watts

25V 50V 0.333A 2.5 Watts 5.0 Watts

25V 50V 0.100A 0.25 Watts 0.50 Watts

Table 12: Loop 1 Heater output ranges.

Full-Scale

Current

Take care to ensure that the proper load resistance is selected. Connection to a 25 load while a 50 is selected will result in overheating and eventual automatic heater shutdown. Conversely, connection to a 50 load while setting a 25 load will result in the dissipation of only one half of the indicated heater power in the load.

Load resistance and Full Scale Output Range are selected via the front panel, or any of the remote interfaces.

Heater output power displays are based on the heater read-back circuitry which measures output current independently of the actual heater circuitry. Thus, heater fault conditions are detected and their corresponding alarms asserted.

Max. Output Power

25 50

i Note: Heater output displays are given as a percentage of output power, not output current. In order to compute actual output power, multiply this percentage by the full-scale power of the selected range. However, to compute actual output current, you must first take the square root of the percentage and then multiply by the full-scale current.

Cryo-con Model 24C Specifications, Features and Functions

Control Loop #2, Secondary Heater Output

Control loop #2 is a constant current source similar to Loop #1.

Range Compliance Full-Scale Current Max. Output Power

High

Low

36V 0.71A 25 Watts

36V 0.22A 2.5 Watts

Table 13: Loop 2 Heater output ranges.

Control Types

There are four control types available in the Model 24C. They are Manual, PID, PID Table, Ramp and Ramp Table. All modes are available on all control loops.

Manual mode operation allows setting the output power manually as a percentage of full-scale power.

PID control allows feedback control using an enhanced PID algorithm that is implemented using 32-bit floating point Digital Signal Processing techniques. Enhancements include:

1. Noise filtering on the derivative term. The D term will provide better control stability, but is often not used because, without filtering, it makes the control loop too sensitive to noise.

2. Integrator wind up compensation. While slewing to a new setpoint, the integrator in the PID loop can build up to a very large value. If no compensation is applied, overshoot and time to stability at the new setpoint can be delayed for an extremely long time. This is especially true in cryogenic environments where process time constants can be very long.

3. Dithering and filtering the outputs in order to increase output resolution and improve control stability.

The PID Table control mode is a PID control loop just as described above. However, it is used to look up PID and heater range values based on the specified setpoint. This is useful where a process must operate over a wide range temperature range since optimum PID values usually change with temperature.

To use the Table mode effectively, the user must first characterize the cryogenic process over the range of temperature that will be used, then generate PID and heater range values for various temperature zones. This is usually done using the autotune capability. Once the information is placed into a PID Table, the Model 24C will control in Table mode by interpolating optimum PID values based on setpoint.

The Model 24C allows for the entry of six independent PID Tables. Each table may contain up to 16 temperature zones.

In the Ramp control mode, the controller approaches a new setpoint at a user specified rate. When this setpoint is reached, the controller will revert to PID control.

Cryo-con Model 24C Specifications, Features and Functions

Alarm Outputs

Alarm outputs include a LED indicator, an audible alarm, on-screen display and remote reporting.

Alarms may be asserted based on high temperature, low temperature, input sensor fault or heater fault conditions.

A user selectable dead-band is applied to all alarms. The High and Low temperature alarms may be latched. See the Input Channel

Configuration Menu.

i Note: To clear a latched alarm, first press the Alarm key and then press the Home key.

Relays

The Model 24C has two dry-contact mechanical relay outputs. Relays are asserted or cleared based on the temperature reading of selected input

channels. Each output has a high and low set-point that may be enabled from the front panel or a remote interface. Furthermore, relays can be manually asserted ON or OFF.

Normally-Open contacts are available on the rear panel. Contact rating is 10A @125 VAC, 5A @250 VAC or 5A @30 VDC for resistive loads. Maximum switching power is 150W.

Remote Interfaces

Ethernet LAN and RS-232 interfaces are standard. IEEE-488.2 (GPIB) and USB are external, field installable options. All functions and read-outs available from the instrument may be completely controlled by any of these interfaces.

The LAN interface is electrically isolated and is 10/100-BaseT compliant. Connection is made via the RJ-45 connector on the rear panel.

The Serial port is an RS-232 standard null modem with male DB9 connector. Rates are 9600, 19,200 and 38,400 Baud.

When installed, the GPIB option is fully IEEE-488.2 compliant. Connection is made at the rear panel's LAN port.

The programming language used by the Model 24C is identical for all interfaces and is SCPI language compliant.

Cryo-con Model 24C Specifications, Features and Functions

Rear Panel

Figure 3: Model 24C Rear Panel Layout

AC Power Connection

The Model 24C requires single-phase AC power of 50 to 60 Hz. Voltages are set by the line voltage selector in the Power Entry Module on the rear panel. The power cord will be a standard detachable 3-prong type.

Line voltage selections are: 100, 120, 220 or 240VAC. Tolerance on voltages is +10% to -5% for specified accuracy and -10% for reduced full-scale heater output in the highest output range.

The power jack and mating plug of the power cable meet Underwriters Laboratories (UL) and International Electrotechnical Commission (IEC) safety standards.

User-replaceable fuses are incorporated in the Power Entry Module.

i Note: The Model 24C uses a smart power on/off scheme. When the power button on the front panel is pressed to turn the unit off, the instrument's setup is copied to flash memory and restored on the next power up. If the front panel button is not used to toggle power to the instrument, the user should configure it and cycle power from the front panel button one time. This will ensure that the proper setup is restored when AC power is applied.

Caution: Protective Ground: To minimize shock hazard, the instrument is equipped with a three-conductor AC power cable. Plug the power cable into an approved three-contact electrical outlet or use a three-contact adapter with the grounding wire (green) firmly connected to an electrical ground (safety ground) at the power outlet.

Cryo-con Model 24C Specifications, Features and Functions

Fuse Replacement and Voltage Selection

Access to the Model 24C's fuses and voltage selector switch is made by using a screwdriver to open fuse drawer in the power entry module. A slot is provided above the voltage selector window for this purpose.

The fuse and voltage selection drawer cannot be opened while the AC power cord is connected.

Voltage selection is performed by rotating the selector cams until the desired voltage shows through the window shown.

There are two fuses that may be removed by pulling out the fuse modules below the voltage selector. Fuses are specified according to the AC power line voltage used.

Line Voltage Fuse Example

100VAC, 120VAC 2.0A slow-blow Littlefuse 313 002

220VAC, 240VAC 1.0A slow-blow Littlefuse 313 001

Table 14. AC Power Line Fuses

Mechanical, Form Factors and Environmental

Enclosure

The Model 24C enclosure is standard 2-U half-width 17-inch rack-mountable type that may be used either stand-alone or incorporated in an instrument rack.

Dimensions are: 8.5"W x 3.5"H x 12"D. Weight is 9 Lbs. An instrument bail and feet are standard. Rack Mount kits are available from Cryo-

con for both single instrument or side-by-side dual configurations. A rack mount kit is optional.

Cryo-con Model 24C Specifications, Features and Functions

Environmental and Safety Concerns.

Safety

The Model 24C protects the operator and surrounding area from electric shock or burn, mechanical hazards, excessive temperature, and spread of fire from the instrument.

 Keep Away From Live Circuits: Operating personnel must not remove

instrument covers. There are no internal user serviceable parts or adjustments. Refer instrument service to qualified maintenance personnel. Do not replace components with power cable connected. To avoid injuries, always disconnect power and discharge circuits before touching them.

 Cleaning: Do not submerge instrument. Clean exterior only with a damp cloth

and mild detergent.

 Grounding: To minimize shock hazard, the instrument is equipped with a

three-conductor AC power cable. Plug the power cable into an approved three-contact electrical outlet only.

Safety Symbols

Cryo-con Model 24C Front Panel Operation

Front Panel Operation

The user interface of the Model 24C Cryogenic Temperature Controller consists of a 40 character by eight line TFT LCD and a keypad. All features and functions of the instrument are accessed via this simple and intuitive menu-driven interface.

Figure 4: Model 24C Front Panel Layout

The Keypad

Function Keys

The Function Keys on the Model 24C are Power , Stop , Control , Home , and Enter . These buttons always perform the same function, regardless of the context of the display.

The Power key is used to turn AC power to the controller on or off. Note that this key must be pressed and held for one second in order to toggle AC power.

i Note: The Model 24C uses a smart power on/off scheme. When the power button on the front panel is pressed to turn the unit off, the instrument's configuration is copied to flash memory and restored on the next power up. If the front panel button is not used to toggle power to the instrument, the user should configure the controller and cycle power from the front panel button one time. This will ensure that the proper setup is restored when AC power is applied.

Cryo-con Model 24C Front Panel Operation

The Stop and Control keys are used to disengage or engage the instrument’s output control loops. Pressing Control will immediately turn on all enabled heater outputs and pressing Stop will turn them both off. To enable or disable an individual loop, go to the Loop Configuration Menu menu and select the desired ‘Type’.

The Home key is used to take the display to one of the Home Status displays. These displays show the full status of the instrument.

The Enter key is used to enter numeric data or selections.

The Keypad and Setup Menu Keys

The keypad keys on the far right side of the instrument serve a dual function. When the display is showing one of the configuration menus, the keypad is used for navigation and data entry. When the display is in the Home Status Display, their function is identified by a label printed just above the key and is as follows:

ChA, ChB, ChC, ChD - Go to the Input Channel Setup

menu.

Loop 1, Loop 2 - Go to the Control Loop Setup menu.

Auto Tune - Go to the auto-tuning menu for either loop.

Config - Go to the User Configurations menu.

Sensors - Go to the Sensors configuration menu, including sensor calibration

curves.

PID Table - Go to the PID tables setup menu.

System - Go to the System setup menu. This includes fields for Remote Input /

Output, Display filters and the Over Temperature Disconnect feature.

Display - Go to the Display setup menu. This allows configuration of the front

panel display from a list of options

Alarm - Go to the Alarm Status menu.

Set Pt - Set the setpoint values for both control loops.

Options - Go to the Options Setup Menu.

Cryo-con Model 24C Front Panel Operation

Keypad Data Entry

The keypad is used to enter data and make selections in the various configuration menus. Fields require the entry of numeric or enumeration data.

Enumeration fields are display fields where the value is one of several specific choices. For instance, the Heater Range field in the Loop 1 setup menu may contain one of only three possible values: HIGH, MID and LOW. There are many enumeration fields that contain only the values ON and OFF.

Enumeration Fields

An enumeration is always indicated by the + character in the first column of the field. To edit an enumeration field, place the cursor at the desired field by using the

Navigation keys. Then, use the + or 0 keys to scroll through all of the possible choices in sequence.

When a field has been changed, the cursor will flash over the + symbol. To select the displayed value, press the Enter key. To cancel selection without updating the field,

press the Esc key.

To select the displayed value, press the Enter key. To cancel selection without updating the field, press the Esc key. The cursor will then return to the + symbol.

Numeric Data Fields

Numeric data is indicated by a pound-sign (#) in the first column of the field. The Keypad Keys are used to enter data into numeric fields. These keys are: the

numerals 0 through 9, the period key (.) and the +/- key. When the cursor is positioned to a field that requires numeric data, the keypad keys

become hot and pressing one of them will result in the field being selected and numeric entry initiated. This is indicated by a flashing cursor.

When the Enter key is pressed, numeric data in the selected field will be checked for range and the instrument’s configuration is correspondingly updated.

i Note: If the numeric entry is outside of the required range, an error is indicated by the display of the previous value of the field.

Cryo-con Model 24C Front Panel Operation

Once the entry of numeric data has started, it can be aborted by pressing the Home key. This will cause the field to be de-selected and its value will be unchanged. Pressing the ESC ( ), key will exit data entry and restore the field to its previous value. The key can be used as a backspace.

i Note: Up to 20 digits may be entered in a numeric field. When digit entry has exceeded the display field width, additional characters will cause the display to scroll from right to left. When entry is complete, the updated display field may not show all of the digits entered because of limited field width, however, the digits are retained to the full precision of the controller's internal 32 bit floating point format.

Cryo-con Model 24C Front Panel Operation

Summary of keypad functions

Key Function Description

Power

Stop

Control

Enter Home

ChA

Esc

Sensors

System

. Display

± Setpoint

0 Alarm 1 ChB 2 ChC 3 ChD 4 Options 5 Loop 1 6 Loop 2 7 Sensors 8 PID Table 9 Auto Tune

Toggle power. Must be held in for two seconds. Disengage all control loops. Engage all control loops. Enter key Go to the Home Status Display. Input Channel Menu for Channel A. / Scroll Display UP If in data entry mode, Escape. Additionally, if the keypad has been

locked by a remote interface, pressing this key will unlock it and clear the Remote LED / Scroll Display DOWN.

Go to the sensor setup menu / Scroll Display RIGHT If in data entry mode, backspace. From home display, go to the

System setup menu / Scroll Display RIGHT. Go to the display configuration menu. Change the setpoint value for either control loop. / Scroll to NEXT

selection. Go to the Alarm Status menu. / Scroll to PREVIOUS selection Input Channel Menu for Channel B. Input Channel Menu for Channel C. Input Channel Menu for Channel D. Options Setup Menu. Loop 3 and 4 setup menus. Go to the Loop 1 setup menu. Go to the Loop 2 setup menu. Sensor data and calibration curve menu. PID table menu. Autotune menu.

Table 15: Keypad key functions.

The LED indicators and Audible Alarm

There are three LED indicators located just below the main display.

The blue Control LED is illuminated whenever either of the control loops are engaged and actively controlling temperature. To disengage the loops, press the Stop key.

The red Alarm LED is illuminated whenever a user programmed alarm has been triggered. To clear the alarm, the enabled event that is asserting the alarm must be disabled. Press the Alarm key to view the status of all alarms.

The green Remote LED can be turned on or off under program control by the remote interface. Use of this LED by a computer connected to the instrument is optional. This LED may also indicate that the keypad is locked out. To clear the LED and the keypad lockout, press the Esc key.

Cryo-con Model 24C Front Panel Operation

The Front Panel Display

Home Status Displays

At the top of the instrument’s menu tree are the home status displays. They can be selected from anywhere in the instrument’s menu tree by pressing the Home key.

The Home display is easily configured to show only desired data. There are four zones, each of which may be independently configured.

Pressing the Display key will list the configuration of each zone. To change the contents of

a zone, scroll to the desired zone and press the Enter key. This will result in a display of all possible selections for the selected zone. A summary of the important selections is given below:

Temperature

Displays an input channel temperature in 2x font. Above the temperature is the input channel indicator, name string and alarm status. Below is the sensor type and excitation level.

Loop Status Displays

These displays show the current status of a selected control loop. The control loop's input temperature is shown in 2x font. Above is the loop and channel indicator, the input channel's name string and alarm status. Below in 1x font is the loop's setpoint, heater range and percent-of-full-scale output power.

1A Sample Holder 2B First Stage

251.445K 296.845K

300.000K 1-Off-Low 100.000K 2-Off-Low C: Second Stage D:Rad Shield

251.445K 296.845K

RO-600 RuOx 10uV R500 RuOx 1.0mV

Home Zone Configuration Menu

Zone 1 Loop 1 Status Zone 2 Loop 2 Status Zone 3 ChC Temperature Zone 4 ChD Temperature

Input Channel Statistics Display

The Channel A, B, C and D statistics displays show the selected input channel temperature, the slope of the temperature history, the minimum and maximum temperatures.

The slope of the temperature history (M) is given in Display Units per Minute.

When any of the statistics pages are displayed, pressing the Enter key will reset the accumulation.

Cryo-con Model 24C Front Panel Operation

Temperature Displays

A typical Input Channel Temperature Display is shown on this page. It consists of the input channel designator, a Temperature reading and the current temperature units.

The temperature, a seven-character field, is affected by the Display Resolution setting in the System menu. This setting may be 1, 2, 3 or Full. Settings of 1, 2, or 3 indicate the number of digits to the right of the decimal point to display whereas the Full setting causes the display to be left justified in order to show the maximum number of significant digits possible.

The Display Resolution setting does not affect the internal accuracy of arithmetic operations. It is generally used to eliminate the display of unnecessary digits that are beyond the sensor’s actual resolution.

If the Input Channel has been disabled, a blank display is shown.

Temperature units are selected in the individual input channel setup menus, ChA , ChB , ChC or ChD. Temperature Units may be K, C or F. When Sensor Units (S) is selected, the raw input

K Kelvin C Celsius F Fahrenheit

Ohms



V Volts

Table 16: Temperature Units

readings are exhibited. These will be in Volts or Ohms.

Sensor Fault Display

A sensor fault condition is identified by a temperature display of seven dash (-) characters as shown here. The sensor is open, disconnected or shorted.



Temperature Out of Range Display If a temperature reading is within the measurement range of the instrument but is not

within the specified Sensor Calibration Curve, a display of seven dot (.) characters is shown.



i Note: In some cases, there will be an erratic temperature display when no sensor is connected. This is not an error condition. The high input impedance of the controller’s input preamplifier causes erratic voltage values when left unconnected. If an input is left unconnected, the sensor type should be set to type "None", which turns the input off.

Cryo-con Model 24C Front Panel Operation

Loop Status Displays

When the Model 24C is not controlling temperature, the status of the Loop output is shown.

The first character of the Loop Status Display is always the loop number, which will be either a superscripted 1 or 2 corresponding to Loop 1 or Loop 2.

The Loop number is accompanied by the heater status as follows:

1. -OFF- Indicates that heater output is functional and the control loop is off or

1

disabled. For the primary heater, Loop 1, the range is also shown. Range settings may

be either Hi, Mid, Low or Min. The range is set in the Loop 1 menu.

For the secondary output, or Loop 2, the range will be shown as Hi or Low. The range is set in the Loop 2 menu.

2. Overtemp indicates that the controller’s Internal Temperature Monitor circuit shut off the heater. This fault is usually the result of a shorted heater or use of a heater with significantly less resistance than the selected load resistance. After the controller has been allowed to cool to an acceptable temperature, pressing the CONTROL button will clear the

1 

error and restore control mode.

3. OTDisconn indicates that the heater output was disconnected by the Over Temperature Disconnect Monitor. This monitor is configured by the user and functions to disable the heater if a specified over temperature condition exists on a selected input channel. See the System menu for information on how to

1 

configure and use this important feature.

If the Model 24C is controlling temperature (loop ON), the heater status display shows the loop output as a percentage of full scale.

This example shows the Heater Status for Loop 2 in a Model 24C controller. The unit is in control mode and is outputting 30% of full scale output current. This means that the output power is

2HI

(30%)^2, or 9% of 25 Watts.

Cryo-con Model 24C Front Panel Operation

Loop Bar Chart Display

The Loop Bar Chart is a 50-segment bar chart that shows the measured output of a selected loop output.

The bar is composed of ten blocks with five segments. Therefore, output current can be read to an accuracy of 2%.

Note that the bar chart does not have a loop number indicator. Some examples are:

Loop ON, zero output:



Loop OFF:

Loop ON, 50% output:





i Note: The Model 24C uses an independent circuit to read current actually flowing through the load. The heater bar graph shows this measured current. If the unit is controlling temperature, but the bar graph indicates zero current flow, an error condition exists, possibly an open heater.

Cryo-con Model 24C Front Panel Menu Operation

Front Panel Menu Operation

Instrument Setup Menus

To access the various instrument setup menus, press one of the Setup Menu keys. The display must be in ‘Home Status’ in order for these keys to be active.

The user may exit a Setup Menu and return to the Home Status display at any time by pressing the Home key.

Menus contain several lines, so scroll through the display using the Navigation keys. The last character of each line in a setup menu is the format indicator. The indicator

will be blank until the cursor is moved to the line. Format indicators are: # - Numeric entry.

+ - Enumeration entry using the + and 0 keys.

- The line is selected by pressing the Select key.

The Setpoint Menu

The setpoint menu is accessed by pressing the Set Pt key. This gives one-key access to the setpoints for all of the control loops.

Press the Home key to exit the menu without update.

The Alarm Status Display Menu

The current status of the temperature alarms may be viewed by pressing the Alarm key.

Alarms are set for each input channel using the Input Channel Setup menu described below.

When an alarm is asserted, the Alarm LED on the front panel will light. Pressing the

Alarm key will display all of the alarms. Status is shown as follows:

— No alarm LO Low temperature alarm HI High temperature alarm

The letter L at the end of the line indicates that the alarm is latched. A latched alarm is asserted when the alarm condition is set. It stays asserted until it is manually cleared by the user.

i Note: To clear a latched alarm, first press the Alarm key to view the alarms and then press the Home key to clear the latch and return to the Home display.

Cryo-con Model 24C Front Panel Menu Operation

Input Channel Configuration Menu

These menus contain all of the user-configurable parameters for a selected sensor input channel.

Use the navigation keys to move around the list.

When the cursor (+) is located to the left of the ChA indicator, channels B, C and D may be displayed by pressing the + key. To

ChA:Sample Holder High Alarm:100.00 + 1.543K -- High Alarm Enable:No Low Alarm: 10.00 Sen:32 RO-600 Low Alarm Enable:No Input Config Deadband: 0.25 CalGen Latched Enable:No Statistics Audible Enable:No

sequence in the reverse direction, press the 0 key.

Input Channel Configuration Menu

Input channel units. Selections are K, C, F or S.

+ 1.543K --

+

Input Config.

CalGen

Statistics



+



+

Deadband: 0.250

+

+

Here, S selects primitive sensor units. When S is selected, the actual sensor units of Volts or Ohms will be displayed.

Sensor type selection. Allows selection of any user or factory installed sensor. The 20 shown indicates that the current sensor is number 20.

Go to the input configuration menu.

Go to the CalGen screen.

Go to the input channel statistics screen.

Setpoint for the High Temperature alarm. Use the keypad for numeric entry and then press the Enter key.

High temperature alarm enable. Selections are Yes or No.

Setpoint for the Low Temperature alarm.

Enables latching alarms on the selected input channel.

Alarm dead-band.

Enables the internal audio alarm to sound on any enabled alarm condition.

Enables or disables latching alarm conditions. A latched alarm is cleared by pressing the Alarm key followed by Home key.

Table 17: Input Channel Configuration Menu

Cryo-con Model 24C Front Panel Menu Operation

Temperature Units Enumeration, Default: K The Temperature Units field (line 1) assigns the units used to display temperature for the input channel. Options are K for Kelvin, C for Celsius, F for Fahrenheit and S for sensor units. Note that if the S option is selected, the actual sensor units will be displayed when the field is deselected. Available sensor units are V for Volts and  for Ohms.

Use the + or 0 key to scroll through all of the options. When the desired units are displayed, press the Enter key to make the selection. The display will now show the current temperature with the new units.

Sensor Type Selection Enumeration Line 2 selects the Sensor type for the input channel. When this field is selected, the scroll keys are used to scroll through all of the available sensor types. Factory installed sensors appear first and then user sensors. For a list of both factory and user sensors, refer to Appendix A.

New user sensor types and calibration curves are added using the Sensors menu.

Setting a Temperature Alarm

The Alarm lines are used to setup alarm conditions. The Model 24C allows alarm conditions to be assigned independently to any of the input channels.

High temperature and low temperature alarms may be entered and enabled. Note that a user selected dead-band is applied to the assertion of high and low temperature alarms.

Alarm conditions are indicated on the front panel by the Alarm LED and various display fields. They are also reported via the remote interfaces.

When the audible alarm is enabled, a high-pitched buzzer will sound when an alarm condition is asserted.

The Model 24C supports latched alarms. These are alarms that remain asserted even after the condition that caused the alarm has been cleared. To clear a latched alarm, first press Alarm to view the Alarm Status Display and then press the Home key to clear.

Input Channel Statistics

The Model 24C continuously tracks temperature history on each input channel. The Input Statistics shown in this menu provides a summary of that history.

The channel history is reset whenever the channel is initialized and can also be reset by pressing the Enter key while the cursor is on any of the statistics lines.

The Accum line shows the length of time that the channel history has been accumulating. It is in units of Minutes.

The Minimum and Maximum temperature lines show the temperatures from during the accumulation time. Values are shown in the currently selected display units.

S2 is the temperature variance, which is computed as standard deviation squared.

The M and b fields display the slope and the offset of the LMS best-fit straight line to the temperature history data.

Cryo-con Model 24C Front Panel Menu Operation

CalGen Sub-menu

Selection of the CalGen field initiates the calibration curve generator feature. This feature is described in the section Using CalGen.

Setting a Temperature Alarm

The Alarm lines are used to setup alarm conditions. The Model 24C allows alarm conditions to be assigned independently to any of the input channels.

High temperature and low temperature alarms may be entered and enabled. Note that there is a 0.25K hysteresis in the assertion of high and low temperature alarms.

Alarm conditions are indicated on the front panel by the Alarm LED and various display fields. They are also reported via the remote interfaces.

When the audible alarm is enabled, a high-pitched buzzer will sound when an alarm condition is asserted.

Loop Configuration Menu

These menus contain all of the user-configurable parameters for the selected control loop.

The Loop 1 menu is used to perform the setup of the primary 25/50 Watt heater output. This display was designed to provide all of the information required to tune heater parameters and is

Loop 1A:Sample Holder Set Pt:300.000K Pgain: 5.0000 Igain: 60.000S Dgain: 7.5000/S Pman: 5.0000% Type: Man Input: ChA

A: 1.234K 1-Off-Low -Htr-Off

Range: LOW PID Table index: 1 Htr Load: 50W Next

rather complex. Loop #1 and #2 menus can be accessed directly from the front panel. Loop #3 and #4

can be accessed by first pressing the Options key. When the cursor is on the top line, the user can scroll through all of the control loop

menus by pressing the + or 0 keys.

Loop 3D:Booster Supply Set Pt:300.000K Pgain: 5.0000 Igain: 60.000S Dgain: 7.5000/S Pman: 5.0000% Type: Man Input: ChD

D: 211.234K 3-Off-Low -Htr-Off

Range: 10VDC PID Table index: 1 Htr Load: N/A Next

Cryo-con Model 24C Front Panel Menu Operation

Loop Configuration Menu

Set Pt:300.000K

A: 299.99K

1-Off-LOW -Htr-Off-









+

+

+







+ 

Numeric setpoint entry.

Indicator of the controlling input channel and it's current temperature.

Status indicator for the control loop.

Proportional gain, or P term for PID control.

Integrator gain term, in Seconds, for PID control.

Derivative gain term, in inverse-Seconds, for PID control.

Output power, as a percent of full scale, when controlling in the Manual mode.

Control input channel, ChA , ChB, ChC or ChD.

Output power range.

Control Type

Power limit as a percent of full scale. On loop 1, this limit only applies to the HI range.

Maximum value allowed for the setpoint on this loop.

Table number for control in Table mode.

Sets the heater load resistance.

Ramp rate in temperature units per minute.

Go to the next page of the control loop setup menu.

Table 18: Control Loop Setup Menus.

Setpoint Numeric Entry

In the first line of this menu the user can change the setpoint, while still viewing the temperature of the controlling source channel. This allows the user to view the temperature without leaving the setup menu.

i Note: Entry of a setpoint can be overridden by the Maximum Setpoint field described below. The instrument will not accept an entry that exceeds the maximum.

Control loop setpoints may also be entered by using the Set Pt key.

Control Loop PID values Numeric Entry The Pgain, Igain and Dgain lines correspond to the Proportional, Integral and Derivative coefficients of the control loop. Pman is the output power that will be applied to the load if the manual control mode is selected.

Values for the Proportional, or P, gain term range from zero to 1000. This is a unitless gain term that is applied to the control loop. Gain is scaled to reflect the actual heater range and the load resistance.

Cryo-con Model 24C Front Panel Menu Operation

Integrator gain values range from zero to 10,000. The units of this term are Seconds. A value of zero turns the integration function off.

Derivative gain values have units of inverse Seconds and may have values from zero to 1000. A value of zero turns the Derivative control function off.

The Pman field is only used when the heater output is in manual control mode. The value is represented in percent of full-scale output power (Watts) and may have values from zero to 100%.

i Note: The Model 24C expresses heater output values in terms of percent of full-scale output power. The actual power, in Watts, applied to the load is proportional to the square-root of output current.

Control Source Input Channel Enumeration The input filed selects the control loop source input. Any input channel may be selected.

Control Loop Range Enumeration, Default: Low The Range field selects the full-scale output for the selected control loop.

Cryo-con Model 24C Front Panel Menu Operation

Control Types Enumeration, Default: Man The Type filed selects the actual control algorithm used for the selected loop.

Loop control modes are:

1. Man for Manual control mode. Here, a constant heater output power is applied when the unit is controlling temperature. The Pman field selects the output as a percentage of full-scale.

2. Table. This is a PID control mode where the PID coefficients are generated from a stored PID table based on setpoint.

3. PID for standard PID control.

4. Off. In this mode, the controller will not apply power on this output channel. Note that the Model 24C is a dual-loop controller. The Off control mode is used if regulation is desired only on the other channel.

5. RampP. This is a temperature ramp mode. When a ramp operation is complete, the controller will revert to standard PID mode control at the final setpoint.

6. RampT. This is a temperature ramp mode that uses the PID tables to generate tuning parameters.

For more information on control algorithms, refer to the Heater Control Types table above.

For more information on temperature ramps, refer to the section on Temperature

Ramping below.

Output Power Limit Numeric entry, Default: 100% The Power Limit field defines the maximum output power that the controller is allowed to output. It is a percent of the maximum allowed output. Maximum value is 100% and minimum is 15%.

The Power Limit is applied to the HI range only.

i Note: Output Power Limit is an important cryostat protection feature. The user is encouraged to apply it.

Maximum Setpoint Numeric Entry, Default: 1000K The Maximum Setpoint field is used to prevent the casual user from inadvertently entering a temperature that might damage the cryostat.

Maximum value is 10,000K and minimum is 0 K. Setpoint values use the temperature units selected for the controlling input channel.

See the section on Temperature Displays.

i Note: The Maximum Setpoint selection is an important cryostat protection feature. The user is encouraged to apply it.

PID Table Index Numeric entry, Default: 0 The PID Table index line is used to identify the number of the user supplied PID Table that will be used when the Table control mode is selected. The Model 24C will store up to six PID Tables. They are numbered zero through five.

Cryo-con Model 24C Front Panel Menu Operation

Heater Resistance Enumeration, Default: 25 The heater resistance field is an enumeration that sets the value of the heater load resistance. Choices are 50 and 25. When 50 is selected, the heater will output a maximum of 50 Volts at 1.0 Ampere or 50 Watts. When 25 Ohms is selected, the maximum heater voltage is 25 Volts and the output power is 25 Watts.

For additional information, please refer to the Loop 1 Heater output ranges or the

Loop 2 Output Ranges tables.

Warning: It is necessary to set the Load resistance field to the actual value of the heater load resistance being used. If an incorrect value is selected, output power indications will be incorrect non-linear heater operation may result. If the actual heater resistance is less than selected, the heater may overheat resulting in an automatic over temperature shutdown.

Ramping Rate Numeric entry, Default: 0.10/min When performing a temperature ramp, the Ramp field defines the ramp rate. Units are display units per minute. In the default case, this means Kelvin per minute.

For more information on temperature ramps, refer to the section on Temperature

Ramping.

Cryo-con Model 24C Front Panel Menu Operation

User Configurations Menu

The User Configurations Menu is displayed by pressing the Config key. It is used to save or restore up to four instrument setups. Each setup saves the entire state of the Model 24C including setpoints, heater configurations, input channel data etc.

User Configurations Menu

1 

ecall

Table 19: User Configurations Menu

Pressing the Enter key saves the instrument setup to the selected configuration number.

Pressing the Enter key restores a saved configuration.

Saving a User Configuration In the Config menu, navigate to the Save field of the desired configuration. Press the Enter key to execute the save.

Restoring a User Configuration

First, press the Config key and navigate to the Recall field of the desired configuration. Press the Enter key to execute the restore.

Cryo-con Model 24C Front Panel Menu Operation

The System Configuration Menu

This menu is accessed by pressing the System key from the Home Status Display. It is used to set many of the instrument’s parameters including display resolution, I/O port settings etc.

System Configuration Menu Display TC: 4S Display Res: 3 Network Config RS232: 9600 GPIB Adrs: 12 Datalog Config Over Temp Config

FW Rev: 1.00A

Pwr Up In Ctl: No AC Line: 60Hz

Date: 08/01/2009 Time: 12:12:42

System Configuration Menu

+Display TC: 4S

+Display Res: 3

Sets the display time constant in seconds. Selections range from 0.5S to 64S

Sets the resolution. Selections are: 1, 2, 3 or Full.

Network Config

+ 

+GPIB Adrs 12

Datalog Config

7 Over Temp Config

FW Rev:1.01A

+Pwr Up In Ctl:

+AC Line: 60Hz

Table 20: System Configuration Menu

Press Enter to go to the network configuration menu.

Sets RS-232 port baud rate

Sets GPIB I/O address. (Note: GPIB is an external option)

Press Enter to go to the data logging setup screen.

Press Enter to go to the Over Temperature Disconnect configuration screen.

Displays the firmware revision level and hardware revision letter.

Power Up Mode. Off for normal operation. On to engage the control loops 10 seconds after power has been turned on.

AC line frequency. Select 50 or 60Hz.

Cryo-con Model 24C Front Panel Menu Operation

Display Time Constant Enumeration, Default: 2 Seconds

The Display TC field is used to set the display time-constant. This is an enumeration field that sets the time constant used for all temperature displays. Choices are 0.5,

1.0, 2.0, 4.0, 8.0, 16.0, 32.0 and 64 Seconds. The time-constant selected is applied to all channels and is used to smooth data in

noisy environments. The filtering only applies to displayed data; it is not used by the control loops.

Display Resolution Enumeration, Default: 3 The Display Resolution line (Display Res) is used to set the temperature resolution of the front panel display. Settings of 1, 2 or 3 will fix the number of digits to the right of the decimal point to the specified value. A setting of FULL will left-justify the display to show maximum resolution possible.

Note that the Display Resolution setting only formats the display as a user convenience. The internal resolution of the Model 24C is not affected by this setting.

Synchronous Filter Configuration Numeric Entry Default: 7 The Synchronous Filter is used to subtract synchronous noise from the input channel. An example of synchronous noise is the thermal signature of a cryocooler.

The default value of 7 taps is used for a line-frequency synchronous cryocooler. Values go from 1 (off) to 25 taps with 25 corresponding to 2.5 seconds of filtering.

This is an advanced setup function. Unless you are familiar with the synchronous noise source that you are trying to remove, leave this field at its default value of 7.

When the number of taps is changed, the control loops will have to be re-tuned because this filter affects the PID values.

AC Line Frequency Selection Enumeration, Default: 60Hz Select the AC power line frequency. Choices are 50 or 60 Hz. This function only affects the operation of the Synchronous Filter described above.

Cryo-con Model 24C Front Panel Menu Operation

Power-up in Control Mode. Default: Off The Auto Ctl: field sets the power up mode of the controller’s loops. Choose ‘Off’ for normal operation where the control loops are engaged by pressing the Control key and disengaged by pressing the Stop key. When on, the controller will power up, then after ten seconds, will automatically engage the control loops.

Caution: When enabled, the Power-Up in Control mode feature causes the controller to engage the control loops automatically whenever AC power is applied. Please exercise caution in the use of this feature.

Over Temperature Disconnect Configuration

Navigate to the OTD Configuration menu by pressing the System key and then selecting the Over Temp Config field.

The Over Temperature Disconnect (OTD) feature monitors a selected input channel for an over temperature condition. If this exists, all heaters outputs are disconnected and the Loop Status indicator is set to "OTDisconn". A mechanical relay is used for the disconnect so that the load is protected, even if the condition was caused by a fault in the controller’s output circuitry.

The OTD must first be configured to monitor one of the input channels. Note that the OTD feature is completely independent of control loop function and may monitor any input.

Next, an OTD Setpoint must be specified. This is the temperature at which an over temperature shut down is asserted. Temperature units are taken from the source input channel.

Finally, the OTD function must be enabled.

Important: The Over Temperature Disconnect is an important cryostat protection feature. The user is encouraged to apply it.

Over Temperature Disconnect Configuration

+ 

+ 

# 

Table 21: Over Temperature Disconnect Configuration

Sets the Over Temperature Disconnect enable. Selections are On or Off.

Sets the Over Temperature Disconnect source input channel. Selections are ChA or ChB.

Sets the Over Temperature Disconnect setpoint temperature.

Cryo-con Model 24C Front Panel Menu Operation

Data Logging Configuration Menu

i Note: This section applies only to the internal data logging feature of the Model 24C. Remote data logging is also supported by the Cryo-con Utility Software program.

The Data Logging Configuration menu is used to start, stop and configure the data logging process. This menu is accessed from the System Menu.

The only user configurable parameter is the Interval in units of seconds. Once this is set, data logging starts when the State is ON and

DataLogging Configuration Menu +State: ON #Interval: 5 Sec Count: 562 Last Log: 8/1/2010 13:15:09 Press Enter to delete data log buffer

stops when the state is OFF. The last line of the field can

be used to clear the buffer. The data logging function records all four input temperatures along with a real-time

clock stamp. The log buffer is circular and contains 1365 entries. Then the maximum number of

entries is exceeded, the oldest samples are written over. The buffer is maintained in Non-Volatile memory and will therefore survive a power failure.

DataLogging Configuration Menu

+State: ON

#Interval:5 Sec

Count:1365 Last Log: 8/1/2010 12:59:50

Turns logging ON and OFF.

Sets the Data Logging interval in units of Seconds. Minimum is 1 and maximum is 99,999.

Number of records in the log buffer.

Date / time stamp of last record recorded.

Press Enter to delete data log buffer

Logged data is read via any of the remote interfaces as follows:

Hyperterminal: Enter the command DLOG?. Note: you should setup a Receive

File to store the data before executing this command because a large volume of data is returned.

Cryocon Utility Software: Click on the Upload Internal Datalog button. This

will enable reading the log buffer to a spreadsheet .csv file.

Note: Reading a full log buffer takes about six minutes on any of the remote interfaces.

Cryo-con Model 24C Front Panel Menu Operation

Network Configuration Menu

Navigate to this menu by pressing the System key and selecting the Network Config field.

Network Configuration Menu

M24C1234

1





#Port: 5000

00:50:C2:6F:40:3F

Instrument name reported over the LAN. May be modified by using the embedded web page.

Network IP address. Numeric entry. Factory default is 192.168.1.5.

Network subnet mask. Numeric entry. Default is

255.255.255.0

Network gateway. Only used if the instrument is to be connected through a gateway to the Internet. Default is 192.168.0.1.

TCP/IP port assignment. Default is 5000. The UDP port assignment is always the TCP/IP port plus 1 (Default: 5001).

Media Access Control (MAC) address. Unique for each instrument.

+DHCP Ena: OFF





Table 22: Network Configuration Menu

Enable DHCP IP address assignment.

Remote I/O: Last command received.

Remote I/O: Last response.

Local Area Network Setup

Setup of the Local Area Network requires a device name, an IP address, a subnet mask and a gateway.

The device name is any 15 character string. It is reported on the display, but can only be changed via a remote command. The name is used by LAN systems that have name servers. In this case, the instrument can be addressed by it's name rather than it's IP address.

The IP address uniquely identifies the instrument on the LAN. The factory default is

192.168.1.5. While any address can be entered, addresses usually begin with

192.168 which is a Class C network. Other addresses are used only when the instrument is directly connected to the Internet.

The subnet mask is used to divide the LAN addresses into segments. The default subnet mask is 255.255.255.0.

A gateway IP address need only be entered if the instrument communicates with the Internet via a gateway. The factory default gateway is 192.168.0.1, which is used in systems with Internet Connection Sharing.

Cryo-con Model 24C Front Panel Menu Operation

PID Tables Menu

The Model 24C can store six user generated PID tables. Each table may have up to sixteen setpoint zones.

Each setpoint zone in a table requires the entry of a setpoint along with corresponding values for P, I, D and full-scale heater range.

When controlling in the Table mode, the Model 24C will derive control loop PID coefficients and heater range by interpolation of the PID Table zones based on that zone’s setpoint.

PID Tables can be used with both control loops. Building a table from the front panel requires the entry of several numeric values. For

this reason, the user may want to consider using one of the remote interfaces. The start, and top level, of this process is the PID Tables menu. Two menu screens

below this are used to enter numeric data. Here is an overview of the process:

1. The PID Tables menu is used to select the PID Table number (zero through three).

2. Once the table is identified, selecting the EDIT PID TABLE line will take the menu used to edit individual lines of the selected table.

3. To enter or edit an entry, set the desired entry index and enter the zone data on the following lines.

4. The last line of this menu is used to save the table when the entire table is complete.

When a table is saved, it is automatically conditioned so that it can be used directly by the control loop software. The conditioning deletes all entries with setpoint values of zero or less and sorts the table based on setpoint. Therefore, an entry may be deleted by setting the setpoint to any negative number.

Cryo-con Model 24C Front Panel Menu Operation

The PID Table Menu

The PID Table Menu is accessed by pressing the PID Table key from the Home Display and then selecting a table.

The first line of this display shows which PID table is being edited. Placing the cursor on this line will allow the user to scroll through all

Edit PID Table 01 Table Index: 00 P: 1.60 I: 160.0S D: 40.0/S SaveTable&Exit

Setpt: 300.00K Ch: Default Range: HI

of the tables.

PID Table Edit Menu

+Table Index #P #I: #D: #SetPt

+Ch:

+Range:

Sets the line number to edit.

P gain value

I value in units of Seconds.

D value in units of inverse-Seconds.

Setpoint in units of temperature.

Input channel. Can be set to any input or to default where default is the input channel shown in the loop setup menu.

Heater range setting.

Table 23: PID Table Edit Menu

Pressing the Esc key from this menu will abort the line entry process and return the display to the PID Table Menu above. Any edits made to the line will be lost.

When a table index is selected, all of the lines on this menu will be updated to show the selected line. Any data in the selected index will be displayed on the following lines.

The following data can be entered into the PID zone: Setpoint (SP), Proportional gain (P), Integral gain (I), Derivative gain (D) and heater range.

To delete a zone from the PID Table, enter zero or a negative number in the setpoint field. These entries will be rejected when the table is conditioned and stored in Flash memory.

Save the entire table by scrolling to the last line, SaveTable&Exit, then press the Enter key.

Cryo-con Model 24C Front Panel Menu Operation

Sensor Setup Menu

The Sensor Setup menu is used to view and edit user temperature sensor data.

The Sensor Header Edit Menu

Pressing the Sensor key from the Home Status Display accesses the Sensor Setup Menu. From there, the Sensor Header Edit Menu can be accessed by by scrolling to the sensor and pressing Enter.

Definition of a sensor requires entering configuration data on this screen followed by entering a calibration curve.

Sensor Header Edit Menu

+

#

+

Sets the Sensor Type.

Sets the sensor Temperature Coefficient and Calibration Curve Multiplier.

Sets Units of the sensor’s Calibration Curve. Choices are: Ohms, Volts and LogOhm.

Table 24: Sensor Setup Menu

The first line on this menu is the sensor table index. Selecting this field allows the user to scroll through all of the sensors configured in the unit, including user sensors. The index is displayed along with the sensor name.

Note: the sensor name may be entered via any of the Remote I/O interfaces, but may not be changed from the front panel.

Sensor Type is an enumeration of all of the basic sensor types supported by the Model 24C. Choices are shown in the Supported Sensor Configurations table above.

The Multiplier field is a floating-point numeric entry and is used to specify the sensor's temperature coefficient and to scale the calibration curve. Negative multipliers imply that the sensor has a negative temperature coefficient. The absolute value of the multiplier scales the calibration curve. For example, the curve for a Platinum sensor that has 100 of resistance at 0C may be used with a 1000 sensor by specifying a multiplier of 10.0. Also note that the temperature coefficient field is only used when the unit is controlling temperature based on the sensor units of Volts or Ohms.

Units is an enumeration field that identifies the primitive units used by the sensor’s calibration curve. Choices are Volts, Ohms and LogOhm. LogOhm selects the base ten logarithm of ohms and is useful with sensors whose resistance vs. temperature curve is logarithmic.

The Calibration Curve Edit menu

From this screen, the user can input individual entries into a sensor calibration curve. Note that these curves can have up to 200 points requiring the entry of 400 floating point numeric values. For lengthy curves, you may want to consider using one of the remote interfaces. Cryocon provides a free PC utility that uploads or downloads curves which can be created by a text editor.

Cryo-con Model 24C Front Panel Menu Operation

The Calibration Curve Edit menu is accessed by pressing the Sensor key, scrolling to the desired curve and then scrolling to the Edit field of that curve.

The procedure for entering or editing a calibration curve is summarized as follows:

1. First, set the index (IX) field to the curve entry that you want to enter. This will cause the display of data at that index.

2. Enter data points values by entering numeric data and pressing Enter.

3. Go to the next index by changing the IX field.

4. When all data points have been entered, the SaveCurve&Exit field is selected to save the curve.

Once complete, the controller will condition the curve by rejecting invalid entries, then sorting the curve in order of ascending sensor unit values. Therefore, an entry may be deleted by placing a zero or negative number in the temperature field.

Calibration Curve Menu









Sets the current index to an entry within the current table. Values are 0 to 159. When the Enter key is pressed, the following lines will display any data corresponding to the selected entry.

Temperature. Units are always in Kelvin.

Sensor reading. Units are taken from the Sensor Setup menu described above and may be Volts, Ohms or Logohms.

Pressing Enter save entered data and exit the menu. To exit without saving, press the Home key.

Table 25: Calibration Curve Menu

Cryo-con Model 24C Front Panel Menu Operation

The Auto Tune Menu

The Model 24C can automatically tune both control loops. For a complete description of the autotune process including configuration of the tuning menus, refer to the section titled autotuning.

The autotuning menu entries are shown below:

Auto Tune Menu

+Autotune: Loop 1

#DeltaP: 5%

Mode: PI-

#Timeout: 180S

Idle Go

#P=

#I=

#D=

Save & Exit

Sets the loop number for autotuning. Each control loop must be tuned separately.

Sets the maximum power delta allowed during the tuning process. Value is a percent of full-scale output power for the selected loop.

Sets autotuning mode. Choices are P, PI or PID.

Sets the autotune timeout in seconds. If the process model has not converged within this time, tuning is aborted.

Pressing Enter will initiate the autotune sequence. The current auto tune state is also shown.

Proportional gain term generated by autotune. This field will be blank until a successful autotune is completed

Integral gain term generated by autotune. This field will be blank until a successful autotune is completed.

Control Type. Selections are: Off, Man, PID, RampP and Table.

Derivative gain term generated by autotune. This field will be blank until a successful autotune is completed.

Table 26: Auto Tune Menu

Cryo-con Model 24C Front Panel Menu Operation

The Options Menu

Press the Options key to access the Options Menu. This will display the following menu:

Options Menu

Relay 1 Relay 2 Control Loop 3 Control Loop 4

Go to the Relay 1 Configuration Menu

Go to the Relay 2 Configuration Menu

Go to the Loop #3 Configuration Menu

Go to the Loop #4 Configuration Menu

The Relay Configuration Menu

The Relay Menu is accessed from the Options Menu described above. It is used to configure two relay outputs of the Model 24C.

Relay Configuration Menu

Rly Status: --+Mode:Auto

+Source:ChA

#High: 200.000

+Enable:

#Low: 100.000

+Enable:No

#Deadband: 0.25

Status of the Relay.

Output mode selection. Modes are: Auto, On and Off.

Select the input channel used as the source for controlling the output.

Set point for the High Temperature output. The output, when enabled, will be asserted when the input temperature is above this value.

High temperature output enable. Selections are Yes or No.

Set point for the Low Temperature output. The output, when enabled, will be asserted when the input temperature is below this value.

Low temperature output enable.

Deadband, or transition band, in units of the controlling input channel.

The first line of the display is an information only line that describes the state of the digital output and the current temperature on the source input channel. It is used to assist in the configuration of the digital outputs. Digital output status indicators are shown in the table below.

The deadband field sets the amount of hysteresis applied to the temperature before a digital output is set or cleared. Units for this field are in the same units as the controlling input channel. For example, if the deadband is set to 0.25K, a high temperature digital output will not assert until the current temperature exceeds the setpoint by 0.25K and will not clear until the temperature is 0.25K below the setpoint.

Cryo-con Model 24C Front Panel Menu Operation

Relay Status Indicators

Relay is in Auto mode and is clear.

---

Relay is asserted by a high temperature condition.

Relay is asserted by a low temperature condition.

Relay is in manual mode and is asserted.

Relay is in manual mode and is clear.

OFF

Table 27: digital output Status Indicators

Relay Modes are as follows:

Digital Output Modes

Auto

OFF

Control

Relay is controlled by enabled high and low setpoints.

Relay is in manual mode and is asserted.

Relay is in manual mode and is clear.

Relay is asserted whenever the controller is in Control mode. Useful in controlling external booster supplies.

Table 28: Digital Output Modes

Cryo-con Model 24C Basic Setup and Operation

Basic Setup and Operation

Configuring a Sensor

Before connecting a new sensor to the Model 24C, the instrument should be configured to support it. Most common sensors are factory installed while others require a simple configuration sequence.

A complete list of sensors installed at the factory is shown in Appendix A. To configure the instrument for one of these sensors, proceed as follows:

1. To install the sensor on Input Channel A, press the ChA key. For Channel B, press the ChB key etc. This will take you to the Input Channel Setup menu for the selected channel. The first line of this display will show the current temperature in real-time and allow you to select the desired display units. Press the + or 0 keys to sequence through the available options and press the Enter key to make the selection.

2. Use the navigation keys to go down to the Sen: filed. Press the + or 0 keys to scroll through all of the sensor types available. When the desired sensor is displayed, press the Enter key to configure the instrument.

Select None to disable the input channel.

At the end of the factory-installed sensors, eight user-installed selections will be shown. The default name for these are User Sensor N. However, this name can be changed to give a better indication of the sensor type that is connected.

For most sensor types installation is now complete; press the Home key to return to the Home Status display. The exceptions are NTC resistor sensors that use constant-voltage AC excitation. With these types of sensors, scroll down to the Bias Voltage field and select the desired constant-voltage excitation level.

i Note: Only NTC resistor sensors require the selection of a Bias Voltage.

Once sensor configuration is complete, review the section on Sensor Connections to connect the sensor to the instrument.

Cryo-con Model 24C Basic Setup and Operation

Using NTC Sensors

Negative-Temperature-Coefficient (NTC) resistors are often used as low temperature thermometers, especially at ultra-low temperature. Their resistance and sensitivity increase dramatically at low temperature but their sensitivity is often relatively poor at warmer temperatures. The Model 24C supports these sensors by using a constantvoltage AC resistance bridge:

● Measurement accuracy and temperature range are improved at low

temperature because sensor self-heating errors are reduced or eliminated.

● Measurement accuracy is improved at warmer temperatures because the

constant voltage circuit increases excitation power in that region.

● The control stability is improved in the warm region since higher excitation

power reduces measurement noise.

● DC offsets in the resistance bridge can cause additional power dissipation at

low excitation levels. The Model 24C holds offsets to a maximum of one-half of the minimum excitation current by use of an offset cancellation feedback loop.

Error Sources in NTC Sensor Measurements

At warm temperatures, the major source of error with NTC sensors is the measurement electronics itself. In a well designed instrument, accuracy is limited to a level established by the measurement's signal-to-noise-ratio, where the signal is the power dissipated in the sensor and noise is the collection of all noise sources. Thus, accuracy is generally improved by increasing the power dissipated in the sensor.

Conversely, at low temperature, NTC resistors have high resistance and the primary source of error is sensor self-heating caused by excitation power. The resistor has high sensitivity in this region, so measurement errors are small when viewed in units of temperature.

Constant-voltage sensor excitation increases signal power at warm temperature, thereby improving measurement accuracy in an area where the sensor is less sensitive. At low temperature, constant voltage excitation reduces the power dissipated in the sensor which reduces accuracy in units of Ohms, but more importantly, reduces sensor self-heating. Since low temperature is the sensor's most sensitive area, temperature measurement accuracy will not be degraded. The result is an accuracy improvement that extends the useful temperature range of a given sensor at both the warm and cold ends.

Cryo-con Model 24C Basic Setup and Operation

NTC Sensor Configuration

NTC sensors are configured by first going to the input channel menu, selecting a NTC sensor and then selecting the Input Config field. An example NTC Input Configuration menu is shown here. A Cryo-con R500 sensor was selected.

Temperature and sensor power dissipation are shown in real-time. Temperature units can be

ChA:Sample Holder NTC Sensor Configuration

+ 0.241K* Pd: 1.66e-10W Bias Voltage: 10mV Bridge Range: Auto

Return to ChA cfg

changed in the real-time temperature display field.

The asterisk (*) character next to the sensor resistance reading indicates that the resistance bridge is not locked. This may indicate that it is still autoranging or that the sensor resistance is too high or too low for the selected voltage bias.

Voltage bias levels are 10mV, 3.0mV, 1.0mV and 300uV. Higher voltages improve accuracy at warm temperature and lower levels reduce self-heating at cold temperature. The user must select a level that maximizes accuracy over the desired temperature range.

Generally, sensors operating above about 2K use the 10mV setting. Below that, selection is more difficult because it depends on the sensor resistance and thermal design. To select a voltage bias in the low temperature region:

1. Establish the sensor at the lowest possible temperature and use the lowest value of bias voltage that will read the sensor's resistance.

2. Increase the voltage bias until a rise in temperature is noted and then reset the bias to the just previous value.

Bridge Range is generally set to Auto but may be set to hold a range in systems where transients due to autoranging are disruptive. Fixed ranges of 1.0mA, 100uA and 10uA are available.

Cryo-con Model 24C Basic Setup and Operation

Using PTC resistor sensors

The Model 24C supports all types of Positive-Temperature-Coefficient resistor sensors. Examples include Platinum and RhodiumIron.

The PTC Sensor Configuration Menu is shown here:

The full-scale input resistance and the excitation level will change depending on the type of PTC sensor selected.

PTC sensor excitation can be either AC or DC. The Model 24Cis calibrated with AC excitation. Switching to DC will introduce a DC offset that will result in temperature measurement errors.

When AC excitation is On, the sensor excitation current is a 7.5 Hz square wave. This square wave excitation generates a small noise signal. Rarely, this signal will be seen up by sensitive measurement equipment in the system. Turning AC excitation Off will eliminate this noise at the cost of introducing a DC offset measurement error.

ChA:Sample Holder PTC Sensor Configuration

+ 241.00K FS Input: 500 Ohms AC Excitation:ON Excitation:1mA Pd: 1.66e-10W

Return to ChA cfg

Cryo-con Model 24C Basic Setup and Operation

Downloading a Sensor Calibration Curve

The Model 24C accommodates up to eight user-defined sensor calibration curves that can be used for custom or calibrated sensors. Since these curves have up to 200 entries, they are usually maintained on a computer as a text file and downloaded to the controller by using the Cryo-con Utility Software. However, curve data may also be entered and edited from the front panel.

Cryo-con sensor calibration curves have a file extension of .crv. They may be opened and edited with any text editor. The format of the file is detailed in Appendix A.

The process for downloading a sensor calibration curve using the Cryo-con utility software is detailed in the section titled Downloading or Uploading a Sensor

Calibration Curve. This section discusses how to set up a curve specifically for

download to the Model 24C. The Cryo-con utility software will read and attempt to parse the following file types:

Sensor Curve File Types

Cryo-con .crv

Lakeshore .340

SI .txt

Other .txt

Directly supported.

Supported. Reads curve data. Header information must be entered by using the header dialog box. The Cryo-con utility software will convert these files into .crv format automatically.

No header information. Columns are reversed from other formats. Must be manually converted to a .crv file before use.

Software will attempt to parse any text file. If the file contains columns of sensor readings vs. temperature, the entries will be properly parsed and the curve can be used or converted to a .crv file after the header dialog box is filled out.

In order to download a file, run the utility software and select 'Sensor Curve Download'. The user will be prompted to select a file. Once the software has read the file, the header information dialog box will appear.

Cryo-con Model 24C Basic Setup and Operation

The Sensor Name can be any string, up to 15 characters, that helps identify the sensor. The Sensor Type, Multiplier and Unit fields affect how the instrument is configured, so they must be correctly set or unexpected results will be obtained.

Sensor Type Multiplier Units Example

Cernox™

Ruthenium-Oxide

Thermistors

Rhodium-Iron 27

CLTS-2B

Germanium

Carbon Glass

Silicon diode

Carbon Ceramic

Platinum 100

Platinum 1K

GaAlAs diode

Table 29: Recommended Sensor Configuration Data

ACR -1.0 LogOhms CX1030E1.crv

ACR -1.0 LogOhms LSRX102.crv

PTC100 1.0 Ohms rhfe27.crv

CLTS 1 Ohms

ACR -1.0 LogOhms LSRX102.crv

Diode -1.0 Volts s900diode.crv

ACR -1.0 LogOhms LSRX102.crv

PTC100 1.0 Ohms PT100385.crv

PTC1K 1.0 Ohms PT1K385.crv

Diode -1.0 Volts s900diode.crv

Note that NTC resistor data is generally in units of LogOhms. However, it can also be in units of Ohms. Be sure to check the curve data for reasonableness.

i Note: One simple way to generate a sensor calibration curve is to open a similar sensor file with a text editor and paste in your own data. The example files in the above table are for that purpose. They are located in the Model 24C sub-directory of the Cryo-con utility software package.

Cryo-con Model 24C Basic Setup and Operation

At this point, it is a good idea to view a graph of the curve data.

The above graph is for a Ruthenium-Oxide sensor with units of LogOhms. It shows the typical highly non-linear curve for that type sensor. If the curve data was in units of Ohms, it would be so extremely non-linear that significant errors might result.

Check the graph for reasonableness and then dismiss it. Proceed with downloading the curve to the instrument. Once complete, check and

verify the result. The curve may be uploaded from the controller by using the Operations>Sensor Curve>Upload function of the utility software. Or it may be manually checked from the controller's front panel by pressing the Sensors key.

Cryo-con Model 24C Basic Setup and Operation

Autotuning

The Autotune Process

In performing autotuning, the Model 24C applies a generated waveform to the heater output and analyzes the resulting changes in process temperature. This is used to develop a process model, then a PID solution.

It is important to note that a range of PID combinations exist, which provide accurate control for a given process. Furthermore, process modeling is a statistical method affected by noise and system non-linearity.

Consequently, multiple autotuning of the same process may yield different results. However, if the process model has not corrupted, any of the generated results will provide equally stable temperature control.

For further explanation, the different PID solutions generated by autotuning vary only in the resultant closed loop bandwidth. Low bandwidth solutions are slower to respond to changes in setpoint or load disturbances. High bandwidth solutions are responsive but can exhibit overshoot and damped oscillation.

The Model 24C attempts to generate minimum overshoot solutions since many cryogenic temperature control applications require this. If the process is noisy, bandwidth is minimized as much as possible. If the process is very quiet, a more aggressive solution is generated subject to the minimum overshoot requirement.

The autotune algorithm produces a heater output waveform in order to force the process model to converge. In general, a large amplitude waveform will provide the best possible signal-to-noise ratio, resulting in a faster and more accurate solution.

However, it is important in some systems for the user to constrain the amplitude and duration of the heater output waveform by using the DeltaP and Timeout parameters.

Small values for DeltaP force the use of small changes in heater power. This makes the process model more susceptible to corruption by noise.

Large values of DeltaP will allow the use of large heater power swings, but this may also drive the process into non-linear operation, which also corrupts the tuning result. Worse, it may allow the application of too much heater power, which causes an over temperature condition.

Experience indicates that most cryogenic systems autotune properly using a DeltaP of 5% whereas a noisy system requires 10% or more. A common example of a noisy cryogenic system is one where a Silicon diode sensor is used with a setpoint near room temperature.

Cryo-con Model 24C Basic Setup and Operation

System Noise and Tuning Modes

Three modes of autotuning may be selected. They are: P only, PI and PID. Using P only autotuning gives the maximum value for P that will not cause oscillation.

The process temperature stabilizes at some point near the setpoint. Using PI or PID control results in stable control at the setpoint. The Derivative, or D, term in PID is used to make the controller more responsive to

changes in setpoint or thermal load. It does not affect the control accuracy when the system has stabilized. However derivative action, by it's nature, amplifies noise. Therefore, PID autotuning and control should only be used with very quiet systems. PI control should be used with all others.

Sensor type has a significant impact on measurement noise. The Model 24C uses a ratiometric technique to measure resistor sensors such as

Thermistors, Platinum RTDs, Carbon Glass etc. This effectively cancels most of the measurement noise and allows effective use of PID control.

Voltage mode sensors, which include diodes and thermocouples, cannot benefit from ratiometric measurement, therefore, PI control is recommended.

It is a very common mistake to attempt PID control using a diode sensor above 70K. This is the least sensitive region of the sensor so measurement noise is very high. PI control is recommended.

Below about 20K, the sensitivity of the diode increases significantly and PID control may be used effectively.

Pre-Tuning and System Stability.

Before autotuning can be initiated by the controller, the system must be stable in terms of both temperature and heater output power. This requires the user to perform a basic pre-tuning operation before attempting the first autotune.

The goal of pre-tuning is to stabilize the process at a temperature near the desired setpoint so that the tuning algorithm can use this as a baseline to model the process.

Cryogenic systems will usually require different PID values at different setpoint temperatures. Therefore, the pre-tuning process should result in a temperature near the desired setpoint.

Pre-tuning does NOT require that the user establish stable control at the target setpoint. This is the job of the autotuning algorithm and is much more difficult than the stability required by pre-tuning.

One method of pre-tuning is to use PID control with a small initial value for P and zero for I and D. This will result in stability at a temperature of the setpoint minus some constant offset. Increasing the P value reduces the offset amount. When P is too large, the system oscillates.

Another pre-tuning technique is to Manual control mode with some fixed value of output power. When the system becomes stable at a temperature corresponding to the set heater power level, a system characterization process is performed using that temperature as an initial setpoint.

Cryo-con Model 24C Basic Setup and Operation

System Characterization.

System characterization is the process of using autotune to generate optimal PID coefficients for each setpoint over a wide range of possible setpoints.

The characterization process is performed once. Then, the setpoints and corresponding generated PID values are transferred to an internal PID table. Thereafter, the system is efficiently controlled using the Table control mode.

Autotune Setup and Execution

The Autotune menu for either control loop is accessed by pressing the Auto Tune key from the Home Operate Screen.

Upon entry, the autotune state variable is set to Idle and the P, I and D fields on the bottom of the display will be blank.

As described above, various setup conditions must be met before autotune can be performed:

1. The Model 24C must be in Control mode.

2. Both the output power and the process temperature must be stable. The user must stabilize the process before the autotune function can accurately model it. If the process is not stable, erroneous values of P, I and D will be generated.

3. The input control channel units must be in temperature, not sensor units of Volts or Ohms. This is because PID control is a linear process and sensor output is generally non-linear. Note that the Model 24C can be manually tuned using sensor units but autotuning cannot be performed.

Cryo-con Model 24C Basic Setup and Operation

Autotune Menu

+

#

+

#















Sets the loop number for autotuning. Each control loop must be tuned separately.

Sets the maximum power delta allowed during the tuning process. Value is a percent of full-scale output power.

Sets autotuning mode. Choices are P, PI or PID.

Sets the autotune timeout in seconds. If the process model has not converged within this time, tuning is aborted.

Real-time display of the temperature on the input channel being tuned.

Pressing Enter will initiate the autotune sequence.

Autotune status. Display only

Proportional gain term generated by autotune. This field will be blank until a successful autotune is completed.

Integral gain term generated by autotune. This field will be blank until a successful autotune is completed.

Derivative gain term generated by autotune. This field will be blank until a successful autotune is completed.

Pressing Enter cause the controller to transfer the generated PID coefficients to the selected loop, initiate control with the new parameters and exit to the Home Operate Display.

Table 30: Autotune Menu

The Delta P field is in percent and is the maximum change in output power that the controller is allowed to apply during the modeling process. A value of 100% allows use of full-scale power increments. A value of 20% uses a maximum power increment of 20% of the current heater output.

The Mode field tells autotune to generate coefficients for P only, PI only, or PID. Choices are: P--, PI- and PID.

The Timeout field is in units of Seconds and indicates the maximum period of time that the process model will run before aborting. This value should be set to at least two or three times the estimated maximum time constant of the process.

i Note: Depending on the setup configuration, the autotune algorithm may apply full-scale heater power to the process for an extended time. Therefore, care should be taken to ensure that autotune does not overheat user equipment. If overheating is a concern, the Over Temperature Disconnect Monitor should be configured to disconnect the heater and abort the autotune process when an input temperature exceeds the specified maximum.

Cryo-con Model 24C Basic Setup and Operation

The autotune sequence is initiated by selecting the Go field. If the initialization of process modeling is successful, the status display line will change from idle to Running. If initialization is not successful, one of the above listed conditions has not been met.

State

Idle

Stabilize

Running

Complete

Idle.

Waiting for input temperature and output power to stabilize.

Actively autotuning.

Successful completion.

Failed due to processing error. Usually,

Failed

this is because the process model did not converge. Try a smaller DeltaP setting.

Abort

Aborted by the user.

Table 31: Autotune States

i Note: When autotuning is initiated, the algorithm will stay in the 'Stabilize' state until the output power and the input temperature are stable. Time in this state is not part of the selected timeout. If the system is not stable, the autotuning process will stay in the Stabilize state indefinitely. To abort, press the Home key.

Cryo-con Model 24C Basic Setup and Operation

When the tuning process is successfully completed, a status of Complete will be indicated and the values of P, I and D will be updated with the generated values. To accept these values and save them as the loop PID coefficients, select the Save&Exit field. To reject the values and exit, press the ESC key.

Autotune may always be aborted by pressing the ESC key. An unsuccessful autotune is indicated by one of the following status lines:

1. Failed. This indicates that the process model did not converge or that PID

values could not be generated from the result.

2. Aborted. Autotune was aborted by user intervention such as pressing the

Stop key.

Temperature Ramping

Operation

The Model 24C performs a temperature ramp function using a specified ramp rate and target setpoint. Once placed in a ramping control mode, a ramp is initiated by changing the setpoint. The unit then progresses to the new setpoint at the selected ramp rate. Upon reaching the new setpoint, ramp mode is terminated and standard PID type regulation will be performed.

Ramping may be independently performed on control loop. The procedure for temperature ramping is as follows:

1. Set the Ramp Rate in the Heater Configuration Menu. This parameter specifies the ramp rate in Units Per Minute, where Units are the measurement units of the input channel controlling the heater. For example, if the input channel units are Kelvin, the ramp rate is in K/min.

2. Select the ramping Control Mode, RampP.

3. Press CONTROL. Now, the controller will begin temperature regulation at the current setpoint.

4. Enter a new setpoint. The controller will enter ramping mode, and ramp to the target setpoint at the specified rate.

5. When the new setpoint is reached, ramping mode terminates and temperature regulation will begin at the new setpoint.

6. Entry of a different setpoint will initiate another ramp.

As a variation on the above procedure:

1. The controller may be regulating temperature in any available control mode. This mode can be changed to a ramping mode without exiting the control loop. This will not result in a ‘glitch’ in heater output power.

2. Once a ramp mode is selected, ramping is performed, as above, by changing the setpoint.

The current status of the ramp function may be seen on the Operate Screen. When a ramp is active, the word RMP will appear in the control loop status displays. It may also be queried via any of the remote ports using the LOOP 1:RAMP? Command.

Cryo-con Model 24C Basic Setup and Operation

Ramping Algorithm

The ramp algorithm uses a basic PID type control loop and continuously varies the setpoint until the specified temperature is reached. This means that the PID control loop will continuously track the moving setpoint. The result is that there will be small time lag between the target ramp and the actual temperature.

Although not normally a problem, the ramp time lag may be minimized by using aggressive PID values. This is accomplished by increasing P, decreasing I and setting D to zero.

Ramping Parameters and Setup

The Ramp Rate is set on the Control Loop Setup menu. Note that the ramp rate on Loop 1 is independent of the rate on Loop 2.

Ramping Example

First, the controller must have PID tuning values that give stable temperature control at both the beginning and end of the ramp. The PID values are usually ‘slow’ (Low values for P, high for I and zero for D). The actual values are not critical, they just need to give stable control.

Next, set the control type to RampP and set the desired ramp rate in the Heater Configuration Menu. Then set the loop setpoint to the starting value for the ramp.

The best way to view a temperature ramp is from the control loop status. Press Loop 1 key to view a screen like this:

Here, the instrument is not controlling temperature and the ramp will start at 180K.

Loop 1A:Sample Holder Set Pt:180.000K Pgain: 5.0000 Igain: 120.00S Dgain: 0.0000/S Pman: 5.0000% Type: RamP Input: ChA

A: 175.234K 1-Off-Low -Htr-Off

Range: HI PID Table index: 1

Htr Load: 50W Next

When the Control button is pressed, the controller will go to the setpoint and control temperature there. It is NOT yet ramping! The display will look like this:

Loop 1A:Sample Holder Set Pt:180.000K Pgain: 5.0000 Igain: 120.00S Dgain: 0.0000/S Pman: 5.0000% Type: RamP Input: ChA

A: 180.000K 51% HI ---|

Range: HI PID Table index: 1

Htr Load: 50W Next

Controlling at 180K but NOT ramping

Cryo-con Model 24C Basic Setup and Operation

Now, you can begin ramping by changing the setpoint to the end of the ramp. The display will indicate that a ramp is in-progress. In this example, the setpoint was changed to 190 and the controller is ramping from 180.000. Notice that the loop status area now indicates a ramp is in progress. The Ramp Pt: field shows where the ramp should be and is continuously updated until the new setpoint is attained. The input temperature should track the Ram Pt: field, indicating that the ramp is progressing as it should.

Loop 1A:Sample Holder Set Pt:190.000K Pgain: 5.0000 Igain: 120.00S Dgain: 0.0000/S Pman: 5.0000% Type: RamP Input: ChA

A: 181.234K Ramp HI ---| Ramp Pt: 181.110 Range: HI PID Table index: 1

Htr Load: 50W Next

Ramping to 190K

Ramping will continue until the setpoint is attained. Then, the loop status will return to normal PID control and the controller will maintain the setpoint.

From here, each time you change the setpoint, the controller will ramp to the

Loop 1A:Sample Holder Set Pt:190.000K Pgain: 5.0000 Igain: 120.00S Dgain: 0.0000/S Pman: 5.0000% Type: RamP Input: ChA

A: 190.000K 58% HI --|

Range: HI PID Table index: 1

Htr Load: 50W Next

new value and control temperature there.

Ramp complete. Controlling at 190K

Summary

To perform a temperature ramp, proceed as follows:

1. Set the control loop P, I and D parameters to allow stable control at both ends of the desired ramp. This is usually done by using ‘slow’ PID values (Low values for P, high for I and zero for D).

2. Set the Ramp Rate in the Heater Configuration Menu. Set the setpoint to the starting value for the ramp.

3. Press CONTROL. Now, the controller will begin temperature regulation at the current setpoint.

4. Enter a new setpoint. The controller will enter ramping mode, and ramp to the target setpoint at the specified rate. The word RMP will appear in the control loop menu.

5. When the new setpoint is reached, ramping mode terminates and temperature regulation begins at the new setpoint.

Cryo-con Model 24C Basic Setup and Operation

Cryocooler Signature Subtraction

Cryocoolers often have a thermal signature that is associated with the mechanical cooling process. At the low end of their temperature range, this signature can have amplitudes of one or more Kelvin.

Since the thermal signature is related to the mechanical cooling process, it is low frequency and has an irregular shape that is rich in harmonics. With most coolers, the frequency will be a sub-multiple of the AC line frequency around 2Hz and the shape will be a narrow spike followed by a long lull.

If a conventional PID control loop is connected to a cryocooler, the thermal signature disrupts the loop and degrades the accuracy of control. If a fast PID loop is used, it attempts to track the signature, which usually results in placing a waveform on the loop output heater that causes control performance to degrade even further.

In still other systems, the thermal signature of the cryocooler is outside of the PID control loop bandwidth enough to cause a phase reversal that actually amplifies the signature causing the entire system to become unstable. These systems oscillate with a sine-wave at a very low frequency.

Faced with a significant thermal signature, users are generally required to de-tune the PID loop and live with the resulting inaccurate control. Here, there is still the possibility of instability.

The Model 24C uses a digital time-synchronous filter to actively subtract the cooler’s signature, resulting in much higher control accuracy and loop responsiveness.

With the Synchronous Filter enabled, the controller synchronously subtracts the thermal signal from the input temperature signal. Since synchronous subtraction is used to eliminate the undesired signature, there is no phase-shift or loss of signal energy, as would be the case if a classical notch or low-pass filter is used.

Subtraction is performed ahead of the PID control loop. Therefore, the input to the loop contains only the baseline temperature signal.

Using the Input Signature Subtraction filter gives much higher temperature measurement accuracy and allows the use of aggressive, high precision control. It is applicable to virtually any cryocooler system.

Synchronous Filter Setup

To use the synchronous filter, two parameters must be set:

 The AC Line Frequency setting must correspond to the actual power input AC

frequency. The filter uses this to synchronize to the cooler.

 The Synchronous Filter Taps parameter must be set for the specific

cryocooler type. This parameter gives the filter a starting point for the number of filter taps required to perform an accurate subtraction. Determination of a proper setting may require some experimentation.

To set the AC Line Frequency, go to the System menu and scroll down to the field AC Line field. Then, select 60 or 50 Hz as required.

 +

Cryo-con Model 24C Basic Setup and Operation

To set the Synchronous Filter Taps parameter, enter a number between 1 and 25 into the Sync Filt. Taps field. A setting of 1 turns the filter off.

Most cryocoolers use a setting of 7 since this is the most common sub-multiple of the AC line frequency applied.

i Note: If you are not using a cryocooler, please leave the Sync Filt. Taps field set at the default of 7.

i Note: If you change the setting the Sync Filt. Taps setting, you will need to re-tune the PID control loop.

Cryo-con Model 24C Basic Setup and Operation

Viewing a Cryocooler Thermal Signature

In order to view a cryocooler’s thermal signature and experiment with the synchronous filter, the Cryo-con Utility Software may be used.

In the Data Logging menu, set the interval field to the minimum allowed value of 0.1 Seconds and then open a strip chart. Use the manual settings on the strip-chart to zoom in on the temperature. The signature with the chart set to the base temperature plus or minus about 0.5K should be observable.

In order to see the cooler signature, set the Sync Filt. Taps field to one. This disables the removal of the signature. From here, you can enter various values in order to see the affect of the synchronous filter.

Shown here is an example of a Cryomech PT403 pulse-tube refrigerator with a very low heat-capacity load. The first part of the graph is with the synchronous filter turned off and the second part shows a setting of 11 taps.

In most cases, a tap setting may be found that completely eliminates the signature.

Cryo-con Model 24C Basic Setup and Operation

Using an external power booster

Some systems require more power than the Model 24C can provide, or require a higher power secondary control loop. An auxiliary DC power supply or amplifier can be used for this purpose.

The non-powered control loops #3 and #4 are designed to drive power supplies that can be programmed by an input voltage. Two output ranges of 5V or 10V are provided to match the inputs of most supplies. Further, either of the Model Model 24C relays can be used to turn the supply on or off.

To configure a supply, simply go to the loop #3 or #4 configuration menu and select a voltage range that matches the supply input requirements. All of the other configuration parameters work the same as they do for loop #1 and #2.

To configure a relay to turn the external supply on or off, go to the relay configuration menu and select a mode of 'Control'. In this mode, the relay will be asserted whenever the instrument is in Control mode.

Power supplies designed for Automatic Test Equipment (ATE) usually have a remote on/off capability that can be controlled by one of the Model 24C's relays. To do this, set the relay mode to Control. In this mode, the relay will assert whenever the Model 24C is controlling temperature and will otherwise clear.

Using CalGen

The CalGen feature is used to generate new calibration curves for Silicon diode, thermocouple or Platinum sensors. This provides a method for obtaining higher accuracy temperature measurements without expensive sensor calibrations.

Most Cryo-con temperature controllers support CalGen directly on the instrument. However, the utility software package implements the same algorithm and can be used with virtually any instrument capable of measuring temperature.

Curves can be generated from any user selected sensor calibration curve and are written to a specified internal user curve location.

For diode sensors the user may specify one, two or three data points. CalGen generates the new curve based on fitting the input curve to the user specified points.

Platinum or thermocouple calibration curves require one or two data points. The generated curve is a best fit of the input curve to the two specified input points.

Since CalGen fits a sensor calibration curve to measured data, any errors in the measurement electronics are also effectively canceled.

i Note: CalGen is re-entrant. Therefore, the user can enter or exit the CalGen menus at any time without loss of previously captured data points. For example, a data point may be captured near 300K, next, the user may exit the CalGen process in order to stabilize the controller near 77K. When the CalGen menu is re-entered for curve generation, the point captured at 300K is still valid.

Cryo-con Model 24C Basic Setup and Operation

CalGen Initial Setup

Generation of a calibration curve using CalGen requires the measurement of various temperature points. Therefore, an input channel must be configured with the correct sensor before the CalGen process can start.

To initiate the curve generation, select the CalGen field on the Input Channel Setup menu. This takes the screen to a sub-menu for the specific sensor type.

i Note: Before CalGen can be initiated, there must be a valid temperature reading on the selected input channel. If this is not the case, selecting the CalGen field will cause the display of an error message.

When the input channel has a valid reading, CalGen determines if the sensor is a diode or Platinum sensor. The calibration curve of the selected input sensor is used as the input to the curve generation process.

Using CalGen With Diode Sensors

Options for generating diode calibration curves are:

1. One point near 300K. The portion of a diode Sensor curve above 30K is fit to a user-specified point near 300K. This is a two-point fit where the 30K point is taken from the existing calibration curve. The portion of the curve below 30K is unaffected.

2. Two points: 300K and 77K. Here, two user-specified points are taken to fit the diode curve region above 30K. The entire curve is offset to match the 77K point, then, the >30K region is fit to the two points.

3. Three points: 300K, 77K and 4.2K. Two points above 30K are fit as in the selection above. Then, a third point is used to fit a single point in the highsensitivity region below 20K.

4. One point near 4.2K. This is a two-point fit where the 20K point is taken from the existing calibration curve. The portion of the curve above 20K is unaffected.

For a diode sensor, a sub-menu is displayed that allows the user to select the number of points desired for the CalGen fit.

1pt CalGen @300K

2pt CalGen

3pt CalGen

1pt CalGen @4.2K

From this screen, select the desired number of points. For example, select ‘2 point’. This will take the display to the two-point curve generator screen shown here.

First CalGen Menu, Diode Sensor

Pressing the Enter key will select curve generation with a single point near 300K.

Pressing the Enter key will select curve generation at two points where both points must be > 50K.

Pressing the Enter key will select curve generation three points: Two above 50K and one near 4.2K.

Pressing the Enter key will select curve generation with a single point near 4.2K.

Table 32: First CalGen Menu, Diode Sensor

Cryo-con Model 24C Basic Setup and Operation

CalGen Menu, 2-point Diode Sensor

The exact temperature at a point near 300K is entered here.

#300.000 Capture

Unit: 0.98257V

#77.000 Capture

Unit: 1.28257V

New Curve

Table 33: CalGen Menu, 2-point Diode Sensor

Note: if CalGen has not been used on this channel before, the word Capture will appear. Otherwise, the last captured sensor reading will appear.

Pressing the Enter key will capture the existing unit reading and associate it with the 300K point. The value will be displayed on line 1 above.

The exact temperature at a point near 77K is entered here.

Pressing the Enter key will capture the existing unit reading and associate it with the 77K point. The value will be displayed on line 3 above.

Pressing the Enter key will initiate the generation of a new curve.

The two temperature points, one near 300K and the other near 77K may be entered in any order.

To enter the 300K-point, change the field 300.000 to the exact required temperature. Then, allow the temperature measurement to stabilize. When the measurement is stable, select the Capture field next to the temperature field. This will cause the Model 24C to capture the sensor reading and associate it with the specified temperature.

When a sensor reading is captured, the actual reading will be displayed in place of the word Capture. Note that the user may capture a new reading by selecting this field again, even if it already contains a reading.

The Unit field of this screen will display the actual sensor reading in real time. This will allow the user to determine when the unit is stable at the required temperature.

Next, the second temperature must be entered in the same way as before.

Cryo-con Model 24C Basic Setup and Operation

When both temperature points have been entered, the user may select the New Curve field in order to generate the new curve. This will cause the display of a menu like the one shown here:

CalGen New Curve Menu

# User Sensor 1

--Save--

Sets the curve number for the generated curve. Numeric entry. Note: only the user curves can be written.

Pressing the Enter key will cause the generation of a new curve. The curve will be stored at the curve number specified on line 1.

Table 34: CalGen New Curve Menu

From this screen, the user must select the target user curve for the generated curve. Finally, select the Save field in order to generate the curve and store it in the selected

user location.

Note: The CalGen process may be aborted by pressing the Esc or Home key.

Using CalGen With Platinum and Resistor Sensors

The calibration curve generation procedure for Platinum or Resistor sensors is the same as for the diode sensors described above. However, these curves are generated using two user specified points. Therefore, the selection of the number of points is not required.

Cryo-con 24C User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual