Lakeshore 331S, 331E User Manual
User’s Manual
Model 331
Temperature Controller
Includes Coverage For:
Model 331S and Model 331E
Lake Shore Cryotronics, Inc.
575 McCorkle Blvd.
Westerville, Ohio 43082-8888 USA
E-mail addresses:
sales@lakeshore.com
service@lakeshore.com
Visit our website at:
www.lakeshore.com
Fax: (614) 891-1392
Telephone: (614) 891-2243
Methods and apparatus disclosed and described herein have been developed solely on company funds of Lake Shore Cryotronics, Inc.
No government or other contractual support or relationship whatsoever has existed which in any way affects or mitigates proprietary
rights of Lake Shore Cryotronics, Inc. in these developments. Methods and apparatus disclosed herein may be subject to U.S. Patents
existing or applied for. Lake Shore Cryotronics, Inc. reserves the right to add, improve, modify, or withdraw functions, design
modifications, or products at any time without notice. Lake Shore shall not be liable for errors contained herein or for incidental or
consequential damages in connection with furnishing, performance, or use of this material.
Revision: 1.9 P/N 119-031 14 May 2009
Lake Shore Model 331 Temperature Controller User’s Manual
1. Lake Shore warrants that this Lake Shore product (the
“Product”) will be free from defects in materials and
workmanship for the Warranty Period specified above (the
“Warranty Period”). If Lake Shore receives notice of any such
defects during the Warranty Period and the Product is shipped
freight prepaid, Lake Shore will, at its option, either repair or
replace the Product if it is so defective without charge to the
owner for parts, service labor or associated customary return
shipping cost. Any such replacement for the Product may be
either new or equivalent in performance to new. Replacement or
repaired parts will be warranted for only the unexpired portion of
the original warranty or 90 days (whichever is greater).
2. Lake Shore warrants the Product only if it has been sold by an
authorized Lake Shore employee, sales representative, dealer
or original equipment manufacturer (OEM).
3. The Product may contain remanufactured parts equivalent to
new in performance or may have been subject to incidental use.
4. The Warranty Period begins on the date of delivery of the
Product or later on the date of installation of the Product if the
Product is installed by Lake Shore, provided that if you schedule
or delay the Lake Shore installation for more than 30 days after
delivery the Warranty Period begins on the 31st day after
delivery.
5. This limited warranty does not apply to defects in the Product
resulting from (a) improper or inadequate maintenance, repair or
calibration, (b) fuses, software and non-rechargeable batteries,
(c) software, interfacing, parts or other supplies not furnished by
Lake Shore, (d) unauthorized modification or misuse, (e)
operation outside of the published specifications or (f) improper
site preparation or maintenance.
6. TO THE EXTENT ALLOWED BY APPLICABLE LAW, THE
ABOVE WARRANTIES ARE EXCLUSIVE AND NO OTHER
WARRANTY OR CONDITION, WHETHER WRITTEN OR
ORAL, IS EXPRESSED OR IMPLIED. LAKE SHORE
SPECIFICALLY DISCLAIMS ANY IMPLIED WARRANTIES OR
CONDITIONS OF MERCHANTABILITY, SATISFACTORY
QUALITY AND/OR FITNESS FOR A PARTICULAR PURPOSE
WITH RESPECT TO THE PRODUCT. Some countries, states
or provinces do not allow limitations on an implied warranty, so
the above limitation or exclusion might not apply to you. This
warranty gives you specific legal rights and you might also have
other rights that vary from country to country, state to state or
province to province.
7. TO THE EXTENT ALLOWED BY APPLICABLE LAW, THE
REMEDIES IN THIS WARRANTY STATEMENT ARE YOUR
SOLE AND EXCLUSIVE REMEDIES.
8. EXCEPT TO THE EXTENT PROHIBITED BY APPLICABLE
LAW, IN NO EVENT WILL LAKE SHORE OR ANY OF ITS
SUBSIDIARIES, AFFILIATES OR SUPPLIERS BE LIABLE FOR
DIRECT, SPECIAL, INCIDENTAL, CONSEQUENTIAL OR
OTHER DAMAGES (INCLUDING LOST PROFIT, LOST DATA
OR DOWNTIME COSTS) ARISING OUT OF THE USE,
INABILITY TO USE OR RESULT OF USE OF THE PRODUCT,
WHETHER BASED IN WARRANTY, CONTRACT, TORT OR
OTHER LEGAL THEORY, AND WHETHER OR NOT LAKE
SHORE HAS BEEN ADVISED OF THE POSSIBILITY OF
SUCH DAMAGES. Your use of the Product is entirely at your
own risk. Some countries, states and provinces do not allow the
exclusion of liability for incidental or consequential damages, so
the above limitation may not apply to you.
LIMITED WARRANTY STATEMENT
WARRANTY PERIOD: ONE (1) YEAR
LIMITED WARRANTY STATEMENT (Continued)
9. EXCEPT TO THE EXTENT ALLOWED BY APPLICABLE LAW,
THE TERMS OF THIS LIMITED WARRANTY STATEMENT DO
NOT EXCLUDE, RESTRICT OR MODIFY, AND ARE IN
ADDITION TO, THE MANDATORY STATUTORY RIGHTS
APPLICABLE TO THE SALE OF THE PRODUCT TO YOU.
CERTIFICATION
Lake Shore certifies that this product has been inspected and
tested in accordance with its published specifications and that this
product met its published specifications at the time of shipment.
The accuracy and calibration of this product at the time of
shipment are traceable to the United States National Institute of
Standards and Technology (NIST); formerly known as the National
Bureau of Standards (NBS).
FIRMWARE LIMITATIONS
Lake Shore has worked to ensure that the Model 331 firmware is
as free of errors as possible, and that the results you obtain from
the instrument are accurate and reliable. However, as with any
computer-based software, the possibility of errors exists.
In any important research, as when using any laboratory
equipment, results should be carefully examined and rechecked
before final conclusions are drawn. Neither Lake Shore nor anyone
else involved in the creation or production of this firmware can pay
for loss of time, inconvenience, loss of use of the product, or
property damage caused by this product or its failure to work, or
any other incidental or consequential damages. Use of our product
implies that you understand the Lake Shore license agreement and
statement of limited warranty.
FIRMWARE LICENSE AGREEMENT
The firmware in this instrument is protected by United States
copyright law and international treaty provisions. To maintain the
warranty, the code contained in the firmware must not be modified.
Any changes made to the code is at the user’s risk. Lake Shore will
assume no responsibility for damage or errors incurred as result of
any changes made to the firmware.
Under the terms of this agreement you may only use the Model
331 firmware as physically installed in the instrument. Archival
copies are strictly forbidden. You may not decompile, disassemble,
or reverse engineer the firmware. If you suspect there are
problems with the firmware, return the instrument to Lake Shore for
repair under the terms of the Limited Warranty specified above.
Any unauthorized duplication or use of the Model 331 firmware in
whole or in part, in print, or in any other storage and retrieval
system is forbidden.
TRADEMARK ACKNOWLEDGMENT
Many manufacturers and sellers claim designations used to
distinguish their products as trademarks. Where those
designations appear in this manual and Lake Shore was aware of
a trademark claim, they appear with initial capital letters and the ™
®
or
symbol.
CalCurve™, Cernox™, Duo-Twist™, Quad-Lead™,
Quad-Twist™, Rox™, and SoftCal™ are trademarks
of Lake Shore Cryotronics, Inc.
MS-DOS
®
and Windows/95/98/NT/2000® are trademarks of
Microsoft Corp.
NI-488.2™ is a trademark of National Instruments.
PC, XT, AT, and PS-2 are trademarks of IBM.
Copyright © 2000 – 2002 & 2004 – 2009 by Lake Shore Cryotronics, Inc. All rights reserved. No portion of this manual
may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical,
photocopying, recording, or otherwise, without the express written permission of Lake Shore.
A
Lake Shore Model 331 Temperature Controller User’s Manual
DECLARATION OF CONFORMITY
We: Lake Shore Cryotronics, Inc.
575 McCorkle Blvd.
Westerville OH 43082-8888 USA
hereby declare that the equipment specified conforms to the following
Directives and Standards:
Application of Council Directives: .............................. 73/23/EEC
89/336/EEC
Standards to which Conformity is declared: .............. EN61010-1:2001
Overvoltage II
Pollution Degree 2
EN61326 A2:2001
Class A
Annex B
Model Number: .......................................................... 331
Ed Maloof
Printed Name
Vice President of Engineering
Position
B
Lake Shore Model 331 Temperature Controller User’s Manual
Electromagnetic Compatibility (EMC) for the Model 331 Temperature Controller
Electromagnetic Compatibility (EMC) of electronic equipment is a growing concern worldwide.
Emissions of and immunity to electromagnetic interference is now part of the design and manufacture
of most electronics. To qualify for the CE Mark, the Model 331 meets or exceeds the requirements of
the European EMC Directive 89/336/EEC as a CLASS A product. A Class A product is allowed to
radiate more RF than a Class B product and must include the following warning:
WARNING: This is a Class A product. In a domestic environment, this product may
cause radio interference in which case the user may be required to take
The instrument was tested under normal operating conditions with sensor and interface cables
attached. If the installation and operating instructions in the User’s Manual are followed, there should
be no degradation in EMC performance.
This instrument is not intended for use in close proximity to RF Transmitters such as two-way radios
and cell phones. Exposure to RF interference greater than that found in a typical laboratory
environment may disturb the sensitive measurement circuitry of the instrument.
Pay special attention to instrument cabling. Improperly installed cabling may defeat even the best
EMC protection. For the best performance from any precision instrument, follow the grounding and
shielding instructions in the User’s Manual. In addition, the installer of the Model 331 should consider
the following:
• Shield measurement and computer interface cables.
• Leave no unused or unterminated cables attached to the instrument.
• Make cable runs as short and direct as possible. Higher radiated emissions is possible with
long cables.
• Do not tightly bundle cables that carry different types of signals.
adequate measures.
C
Lake Shore Model 331 Temperature Controller User’s Manual
TABLE OF CONTENTS
Chapter/Paragraph Title Page
1 INTRODUCTION .................................................................................................................................................... 1-1
1.0 PRODUCT DESCRIPTION ............................................................................................................... 1-1
1.1 SENSOR SELECTION ...................................................................................................................... 1-4
1.2 SPECIFICATIONS ............................................................................................................................. 1-6
1.3 SAFETY SUMMARY ......................................................................................................................... 1-9
1.4 SAFETY SYMBOLS ........................................................................................................................ 1-10
2 COOLING SYSTEM DESIGN ................................................................................................................................. 2-1
2.0 GENERAL ......................................................................................................................................... 2-1
2.1 TEMPERATURE SENSOR SELECTION .......................................................................................... 2-1
2.1.1 Temperature Range ....................................................................................................................... 2-1
2.1.2 Sensor Sensitivity .......................................................................................................................... 2-1
2.1.3 Environmental Conditions .............................................................................................................. 2-2
2.1.4 Measurement Accuracy ................................................................................................................. 2-2
2.1.5 Sensor Package ............................................................................................................................. 2-2
2.2 CALIBRATED SENSORS ................................................................................................................. 2-2
2.2.1 Traditional Calibration .................................................................................................................... 2-2
2.2.2 SoftCal™........................................................................................................................................ 2-3
2.2.3 Standard Curves ............................................................................................................................ 2-3
2.2.4 CalCurve™ .................................................................................................................................... 2-3
2.3 SENSOR INSTALLATION ................................................................................................................. 2-5
2.3.1 Mounting Materials ......................................................................................................................... 2-5
2.3.2 Sensor Location ............................................................................................................................. 2-5
2.3.3 Thermal Conductivity ..................................................................................................................... 2-5
2.3.4 Contact Area .................................................................................................................................. 2-5
2.3.5 Contact Pressure ........................................................................................................................... 2-6
2.3.6 Lead Wire....................................................................................................................................... 2-6
2.3.7 Lead Soldering ............................................................................................................................... 2-7
2.3.8 Heat Sinking Leads ........................................................................................................................ 2-7
2.3.9 Thermal Radiation .......................................................................................................................... 2-7
2.4 HEATER SELECTION AND INSTALLATION .................................................................................... 2-7
2.4.1 Heater Resistance and Power ....................................................................................................... 2-7
2.4.2 Heater Location .............................................................................................................................. 2-8
2.4.3 Heater Types ................................................................................................................................. 2-8
2.4.4 Heater Wiring ................................................................................................................................. 2-8
2.5 CONSIDERATIONS FOR GOOD CONTROL ................................................................................... 2-8
2.5.1 Thermal Conductivity ..................................................................................................................... 2-8
2.5.2 Thermal Lag ................................................................................................................................... 2-8
2.5.3 Two-Sensor Approach ................................................................................................................... 2-9
2.5.4 Thermal Mass ................................................................................................................................ 2-9
2.5.5 System Nonlinearit y ....................................................................................................................... 2-9
2.6 PID CONTROL .................................................................................................................................. 2-9
2.6.1 Proportional (P) ............................................................................................................................ 2-10
2.6.2 Integral (I)..................................................................................................................................... 2-10
2.6.3 Derivative (D) ............................................................................................................................... 2-10
2.6.4 Manual Heater Power (MHP) Output ........................................................................................... 2-10
2.7 MANUAL TUNING ........................................................................................................................... 2-12
2.7.1 Setting Heater Range .................................................................................................................. 2-12
2.7.2 Tuning Proportional ...................................................................................................................... 2-12
2.7.3 Tuning Integral ............................................................................................................................. 2-13
2.7.4 Tuning Derivative ......................................................................................................................... 2-13
2.8 AUTOTUNING ................................................................................................................................. 2-13
2.9 ZONE TUNING ................................................................................................................................ 2-14
Table of Contents i
Lake Shore Model 331 Temperature Controller User’s Manual
TABLE OF CONTENTS (Continued)
Chapter/Paragraph Title Page
3 INSTALLATION ...................................................................................................................................................... 3-1
3.0 GENERAL ......................................................................................................................................... 3-1
3.1 INSPECTION AND UNPACKING ...................................................................................................... 3-1
3.2 REPACKAGING FOR SHIPMENT .................................................................................................... 3-1
3.3 REAR PANEL DEFINITION ............................................................................................................... 3-2
3.4 LINE INPUT ASSEMBLY ................................................................................................................... 3-3
3.4.1 Line Voltage ................................................................................................................................... 3-3
3.4.2 Line Fuse and Fuse Holder ............................................................................................................ 3-3
3.4.3 Power Cord .................................................................................................................................... 3-3
3.4.4 Power Switch ................................................................................................................................. 3-4
3.5 DIODE/RESISTOR SENSOR INPUTS .............................................................................................. 3-4
3.5.1 Sensor Input Connector and Pinout ............................................................................................... 3-4
3.5.2 Sensor Lead Cable ........................................................................................................................ 3-5
3.5.3 Grounding and Shielding Sensor Leads ......................................................................................... 3-5
3.5.4 Sensor Polarity ............................................................................................................................... 3-5
3.5.5 Four-Lead Sensor Measurement ................................................................................................... 3-6
3.5.6 Two-Lead Sensor Measurement .................................................................................................... 3-6
3.5.7 Lowering Measurement Noise........................................................................................................ 3-6
3.6 THERMOCOUPLE SENSOR INPUTS .............................................................................................. 3-7
3.6.1 Sensor Input Terminals .................................................................................................................. 3-7
3.6.2 Thermocouple Installation .............................................................................................................. 3-7
3.6.3 Grounding and Shielding ................................................................................................................ 3-7
3.7 HEATER OUTPUT SETUP ............................................................................................................... 3-8
3.7.1 Loop 1 Output ................................................................................................................................ 3-8
3.7.2 Loop 1 Heater Output Connector ................................................................................................... 3-8
3.7.3 Loop 1 Heater Output Wiring ......................................................................................................... 3-8
3.7.4 Loop 1 Heater Output Noise .......................................................................................................... 3-9
3.7.5 Loop 2 Output ................................................................................................................................ 3-9
3.7.6 Loop 2 Output Resistance .............................................................................................................. 3-9
3.7.7 Loop 2 Output Connector ............................................................................................................... 3-9
3.7.8 Loop 2 Heater Protection ............................................................................................................... 3-9
3.7.9 Boosting the Output Power ............................................................................................................ 3-9
3.8 ANALOG OUTPUT .......................................................................................................................... 3-10
3.9 RELAYS .......................................................................................................................................... 3-10
3.10 INITIAL SETUP AND SYSTEM CHECKOUT PROCEDURE .......................................................... 3-11
4 OPERATION ........................................................................................................................................................... 4-1
4.0 GENERAL ......................................................................................................................................... 4-1
4.1 FRONT PANEL DESCRIPTION ........................................................................................................ 4-1
4.1.1 Keypad Definitions ......................................................................................................................... 4-1
4.1.2 Annunciators .................................................................................................................................. 4-3
4.1.3 General Keypad Operation ............................................................................................................ 4-3
4.1.4 Display Definition ........................................................................................................................... 4-4
4.2 TURNING POWER ON ..................................................................................................................... 4-4
4.3 DISPLAY FORMAT AND SOURCE (UNITS) SELECTION ............................................................... 4-5
4.4 INPUT SETUP ................................................................................................................................... 4-7
4.4.1 Diode Sensor Input Setup - 10 µA Excitation Current .................................................................... 4-7
4.4.2 Diode Sensor Input Setup - 1 mA Excitation Current ..................................................................... 4-8
4.4.3 Resistor Sensor Input Setup .......................................................................................................... 4-9
4.4.3.1 Thermal EMF Compensation ...................................................................................................... 4-9
4.4.4 Thermocouple Sensor Input Setup ............................................................................................... 4-10
4.4.4.1 Room-Temperature Compensation .......................................................................................... 4-10
4.4.4.2 Room-Temperature Calibration Procedure ............................................................................... 4-11
4.5 CURVE SELECTION ....................................................................................................................... 4-12
4.5.1 Diode Sensor Curve Selection ..................................................................................................... 4-13
ii Table of Contents
Lake Shore Model 331 Temperature Controller User’s Manual
TABLE OF CONTENTS (Continued)
Chapter/Paragraph Title Page
4.5.2 Resistor Sensor Curve Selection ................................................................................................. 4-13
4.5.3 Thermocouple Sensor Curve Selection ....................................................................................... 4-13
4.6 TEMPERATURE CONTROL ........................................................................................................... 4-14
4.6.1 Control Loops ............................................................................................................................... 4-14
4.6.2 Control Modes .............................................................................................................................. 4-15
4.6.3 Tuning Modes .............................................................................................................................. 4-15
4.7 CONTROL SETUP .......................................................................................................................... 4-15
4.8 MANUAL TUNING ........................................................................................................................... 4-17
4.8.1 Manually Setting Proportional (P) ................................................................................................ 4-17
4.8.2 Manually Setting Integral (I) ......................................................................................................... 4-17
4.8.3 Manually Setting Derivative (D) .................................................................................................... 4-18
4.8.4 Setting Manual Heater Power (MHP) Output ............................................................................... 4-18
4.9 AUTOTUNE (CLOSED-LOOP PID CONTROL) .............................................................................. 4-19
4.10 ZONE SETTINGS (CLOSED-LOOP CONTROL) ............................................................................ 4-20
4.11 SETPOINT....................................................................................................................................... 4-23
4.12 RAMP .............................................................................................................................................. 4-24
4.13 HEATER RANGE AND HEATER OFF ............................................................................................ 4-25
4.14 MATH .............................................................................................................................................. 4-26
4.14.1 Max/Min ....................................................................................................................................... 4-26
4.14.2 Linear ........................................................................................................................................... 4-27
4.14.3 Filter ............................................................................................................................................. 4-28
4.15 ALARMS AND RELAYS .................................................................................................................. 4-29
4.15.1 Alarms .......................................................................................................................................... 4-29
4.15.2 Relays .......................................................................................................................................... 4-31
4.16 ANALOG OUTPUT .......................................................................................................................... 4-32
4.16.1 Analog Output In Input Mode ....................................................................................................... 4-32
4.16.2 Analog Output In Manual Mode ................................................................................................... 4-34
4.16.3 Analog Output In Loop 2 Mode .................................................................................................... 4-35
4.17 LOCKING AND UNLOCKING THE KEYPAD .................................................................................. 4-35
4.18 DISPLAY BRIGHTNESS ................................................................................................................. 4-36
4.19 REMOTE/LOCAL ............................................................................................................................ 4-36
4.20 INTERFACE .................................................................................................................................... 4-36
4.21 DEFAULT VALUES ......................................................................................................................... 4-37
5 ADVANCED OPERATION ..................................................................................................................................... 5-1
5.0 GENERAL ......................................................................................................................................... 5-1
5.1 CURVE NUMBERS AND STORAGE ................................................................................................ 5-1
5.1.1 Curve Header Parameters ............................................................................................................. 5-1
5.1.2 Curve Breakpoints ......................................................................................................................... 5-2
5.2 FRONT PANEL CURVE ENTRY OPERATIONS .............................................................................. 5-2
5.2.1 Edit Curve ...................................................................................................................................... 5-4
5.2.1.1 Thermocouple Curve Considerations ......................................................................................... 5-5
5.2.2 Erase Curve ................................................................................................................................... 5-6
5.2.3 Copy Curve .................................................................................................................................... 5-6
5.3 SOFTCAL™ ...................................................................................................................................... 5-7
5.3.1 SoftCal With Silicon Diode Sensors ............................................................................................... 5-7
5.3.2 SoftCal Accuracy With Silicon Diode Sensors ............................................................................... 5-8
5.3.3 SoftCal With Platinum Sensors ...................................................................................................... 5-9
5.3.4 SoftCal Accuracy With Platinum Sensors ...................................................................................... 5-9
5.3.5 SoftCal Calibration Curve Creation .............................................................................................. 5-10
6 COMPUTER INTERFACE OPERATION ................................................................................................................ 6-1
6.0 GENERAL ......................................................................................................................................... 6-1
6.1 IEEE-488 INTERFACE ...................................................................................................................... 6-1
6.1.1 IEEE-488 Interface Parameters ..................................................................................................... 6-2
6.1.2 IEEE-488 Command Structure ....................................................................................................... 6-2
Table of Contents iii
Lake Shore Model 331 Temperature Controller User’s Manual
TABLE OF CONTENTS (Continued)
Chapter/Paragraph Title Page
6.1.2.1 Bus Control Commands ............................................................................................................. 6-2
6.1.2.2 Common Commands .................................................................................................................. 6-3
6.1.2.3 Device Specific Commands ........................................................................................................ 6-3
6.1.2.4 Message Strings ......................................................................................................................... 6-3
6.1.3 Status Registers ............................................................................................................................. 6-4
6.1.3.1 Status Byte Register and Service Request Enable Register ...................................................... 6-4
6.1.3.2 Standard Event Status Register and Standard Event Status Enable Register ........................... 6-4
6.1.4 IEEE Interface Example Programs ................................................................................................. 6-5
6.1.4.1 IEEE-488 Interface Board Installation for Visual Basic Program ................................................ 6-5
6.1.4.2 Visual Basic IEEE-488 Interface Program Setup ........................................................................ 6-7
6.1.4.3 IEEE-488 Interface Board Installation for Quick Basic Program ............................................... 6-10
6.1.4.4 Quick Basic Program ................................................................................................................ 6-10
6.1.4.5 Program Operation ................................................................................................................... 6-13
6.1.5 Troubleshooting ........................................................................................................................... 6-13
6.2 SERIAL INTERFACE OVERVIEW .................................................................................................. 6-14
6.2.1 Physical Connection ..................................................................................................................... 6-14
6.2.2 Hardware Support ........................................................................................................................ 6-14
6.2.3 Character Format ......................................................................................................................... 6-15
6.2.4 Message Strings .......................................................................................................................... 6-15
6.2.5 Message Flow Control ................................................................................................................. 6-16
6.2.6 Changing Baud Rate .................................................................................................................... 6-16
6.2.7 Serial Interface Example Programs .............................................................................................. 6-17
6.2.7.1 Visual Basic Serial Interface Program Setup ............................................................................ 6-17
6.2.7.2 Quick Basic Serial Interface Program Setup ............................................................................ 6-20
6.2.7.3 Program Operation ................................................................................................................... 6-21
6.2.8 Troubleshooting ........................................................................................................................... 6-21
6.3 COMMAND SUMMARY .................................................................................................................. 6-22
6.3.1 Interface Commands (Alphabetical Listing) .................................................................................. 6-24
7 OPTIONS AND ACCESSORIES ............................................................................................................................ 7-1
7.0 GENERAL ......................................................................................................................................... 7-1
7.1 MODELS ........................................................................................................................................... 7-1
7.2 OPTIONS .......................................................................................................................................... 7-1
7.3 ACCESSORIES ................................................................................................................................. 7-2
7.4 MODEL 3003 HEATER OUTPUT CONDITIONER ............................................................................ 7-4
8 SERVICE ................................................................................................................................................................ 8-1
8.0 GENERAL ......................................................................................................................................... 8-1
8.1 ELECTROSTATIC DISCHARGE ....................................................................................................... 8-1
8.1.1 Identification of Electrostatic Discharge Sensitive Components ..................................................... 8-1
8.1.2 Handling Electrostatic Discharge Sensitive Components ............................................................... 8-1
8.2 LINE VOLTAGE SELECTION ........................................................................................................... 8-2
8.3 FUSE REPLACEMENT ..................................................................................................................... 8-2
8.4 REAR PANEL CONNECTOR DEFINITIONS .................................................................................... 8-3
8.4.1 Serial Interface Cable Wiring ......................................................................................................... 8-5
8.4.2 IEEE-488 Interface Connector ....................................................................................................... 8-6
8.5 TOP OF ENCLOSURE REMOVE AND REPLACE PROCEDURE .................................................... 8-7
8.6 FIRMWARE AND NOVRAM REPLACEMENT .................................................................................. 8-7
8.7 JUMPERS ......................................................................................................................................... 8-8
8.8 ERROR MESSAGES ......................................................................................................................... 8-8
8.9 CALIBRATION PROCEDURE ......................................................................................................... 8-10
8.9.1 Equipment Required for Calibration ............................................................................................. 8-10
8.9.2 Diode/Resistor Sensor Input Calibration ...................................................................................... 8-11
8.9.2.1 Sensor Input Calibration Setup and Serial Communication Verification ................................... 8-11
8.9.2.2 10 µA Current Source Calibration and 1 mA Current Source Verification ................................. 8-11
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Lake Shore Model 331 Temperature Controller User’s Manual
Chapter/Paragraph Title Page
8.9.2.3 Diode Input Ranges Calibration ................................................................................................ 8-12
8.9.2.4 Resistive Input Ranges Calibration .......................................................................................... 8-13
8.9.3 Diode Sensor Input Calibration - 1 mA Excitation Current ........................................................... 8-14
8.9.4 Thermocouple Sensor Input Calibration ....................................................................................... 8-14
8.9.4.1 Sensor Input Calibration Setup ................................................................................................. 8-14
8.9.4.2 Thermocouple Input Ranges Calibration .................................................................................. 8-14
8.9.5 Analog Output Calibration (Model 331S Only) ............................................................................. 8-15
8.9.5.1 Analog Output Calibration ........................................................................................................ 8-16
8.9.6 Calibration Specific Interface Commands .................................................................................... 8-17
APPENDIX A – GLOSSARY OF TERMINOLOGY ........................................................................................................ A-1
APPENDIX B – TEMPERATURE SCALES .................................................................................................................. B-1
APPENDIX C – HANDLING OF LIQUID HELIUM AND NITROGEN ............................................................................ C-1
APPENDIX D – CURVE TABLES ................................................................................................................................. D-1
LIST OF ILLUSTRATIONS
Figure No. Title Page
1-1 Model 331S Rear Panel Connections .......................................................................................................... 1-3
2-1 Silicon Diode Sensor Calibrations and CalCurve ......................................................................................... 2-4
2-2 Typical Sensor Installation In A Mechanical Refrigerator ............................................................................. 2-6
2-3 Examples of PID Control ............................................................................................................................ 2-11
3-1 Model 331 Rear Panel .................................................................................................................................. 3-2
3-2 Line Input Assembly ..................................................................................................................................... 3-3
3-3 Diode/Resistor Input Connector ................................................................................................................... 3-4
3-4 Thermocouple Input Definition and Common Connector Polarities .............................................................. 3-7
3-5 RELAYS and ANALOG OUTPUT Terminal Block ...................................................................................... 3-10
4-1 Model 331 Front Panel ................................................................................................................................. 4-1
4-2 Display Definition ......................................................................................................................................... 4-4
4-3 Display Format Definition ............................................................................................................................. 4-5
4-4 Record of Zone Settings ............................................................................................................................. 4-22
4-5 Deadband Example .................................................................................................................................... 4-29
4-6 Relay Settings ............................................................................................................................................ 4-31
5-1 SoftCal Temperature Ranges for Silicon Diode Sensors .............................................................................. 5-8
5-2 SoftCal Temperature Ranges for Platinum Sensors..................................................................................... 5-9
6-1 GPIB Setting Configuration .......................................................................................................................... 6-6
6-2 DEV 12 Device Template Configuration ....................................................................................................... 6-6
6-3 Typical National Instruments GPIB Configuration from IBCONF.EXE........................................................ 6-11
7-1 Model 331 Sensor and Heater Cable Assembly ........................................................................................... 7-4
7-2 Model 3003 Heater Output Conditioner ........................................................................................................ 7-4
7-3 Model RM-1/2 Rack-Mount Kit ..................................................................................................................... 7-5
7-4 Model RM-2 Dual Rack-Mount Kit ................................................................................................................ 7-6
8-1 Power Fuse Access ...................................................................................................................................... 8-2
8-2 Sensor INPUT A and B Connector Details ................................................................................................... 8-3
8-3 HEATER OUTPUT Connector Details .......................................................................................................... 8-3
8-4 RELAYS and ANALOG OUTPUT Terminal Block ........................................................................................ 8-4
8-5 RS-232 Connector Details ............................................................................................................................ 8-4
8-6 IEEE-488 Rear Panel Connector Details ...................................................................................................... 8-6
8-7 Location of Internal Components ................................................................................................................. 8-9
B-1 Temperature Scale Comparison .................................................................................................................. B-1
C-1 Typical Cryogenic Storage Dewar ................................................................................................................ C-1
TABLE OF CONTENTS (Continued)
Table of Contents v
Lake Shore Model 331 Temperature Controller User’s Manual
LIST OF TABLES
Table No. Title Page
1-1 Sensor Temperature Range ......................................................................................................................... 1-4
1-2 Typical Sensor Performance ........................................................................................................................ 1-5
1-3 Input Specifications ...................................................................................................................................... 1-6
1-4 Sensor Input Configuration ........................................................................................................................... 1-6
1-5 Heater Output ............................................................................................................................................... 1-7
1-6 Loop 1 Full Scale Heater Power at Typical Resistance ................................................................................ 1-7
4-1 Sensor Input Types ...................................................................................................................................... 4-7
4-2 Sensor Curves ............................................................................................................................................ 4-12
4-3 Comparison of Control Loops 1 and 2 ........................................................................................................ 4-14
4-4 Linear Equation Configuration .................................................................................................................... 4-27
4-5 Default Values ............................................................................................................................................ 4-38
5-1 Curve Header Parameters ............................................................................................................................ 5-3
5-2 Recommended Curve Parameters ............................................................................................................... 5-3
6-1 IEEE-488 Interface Program Control Properties ........................................................................................... 6-8
6-2 Visual Basic IEEE-488 Interface Program .................................................................................................... 6-9
6-3 Quick Basic IEEE-488 Interface Program ................................................................................................... 6-12
6-4 Serial Interface Specifications .................................................................................................................... 6-15
6-5 Serial Interface Program Control Properties ............................................................................................... 6-18
6-6 Visual Basic Serial Interface Program ........................................................................................................ 6-19
6-7 Quick Basic Serial Interface Program ......................................................................................................... 6-20
6-8 Command Summary .................................................................................................................................. 6-23
8-1 Calibration Table for Diode Ranges ........................................................................................................... 8-12
8-2 Calibration Table for Resistive Ranges ...................................................................................................... 8-14
8-3 Calibration Table for Thermocouple Ranges .............................................................................................. 8-15
B-1 Temperature Conversion Table .................................................................................................................... B-2
C-1 Comparison of Liquid Helium and Liquid Nitrogen ...................................................................................... C-1
D-1 DT-470 Silicon Diode Curve ........................................................................................................................ D-1
D-2 DT-670 Silicon Diode Curve ................................................................................................
D-3 DT-500 Series Silicon Diode Curves ........................................................................................................... D-2
D-4 PT-100/-1000 Platinum RTD Curves ........................................................................................................... D-3
D-5 RX-102A Rox™ Curve ................................................................................................................................ D-4
D-6 RX-202A Rox™ Curve ................................................................................................................................ D-5
D-7 Type K Thermocouple Curve ....................................................................................................................... D-6
D-8 Type E Thermocouple Curve ....................................................................................................................... D-7
D-9 Type T Thermocouple Curve ....................................................................................................................... D-8
D-10 Chromel-AuFe 0.03% Thermocouple Curve ................................................................................................ D-9
D-11 Chromel-AuFe 0.07% Thermocouple Curve .............................................................................................. D-10
........................ D-2
vi Table of Contents
Lake Shore Model 331 Temperature Controller User’s Manual
CHAPTER 1
INTRODUCTION
1.0 PRODUCT DESCRIPTION
The Model 331 Temperature Controller combines the easy operation and unsurpassed reliability of the
Model 330 with improved sensor input and interface flexibility, including compatibility with negative
temperature coefficient (NTC) resistance temperature detectors (RTDs). Backed by the Lake Shore
tradition of excellence in cryogenic sensors and instrumentation, the Model 331 Temperature Controller
sets the standard for mid-price range temperature control instruments.
The Model 331 Temperature Controller is available in two versions. The Model 331S is fully equipped
for interface and control flexibility. The Model 331E shares measurement and display capability with the
Model 331S, but does not include the IEEE-488 interface, relays, analog voltage output, or a second
control loop.
Sensor Inputs
The Model 331 Temperature Controller is designed for high performance over a wide operating
temperature range and in difficult sensing conditions. The Model 331 features two inputs, with a highresolution 24-bit analog-to-digital converter and separate current source for each input. Sensors are
optically isolated from other instrument functions for quiet and repeatable sensor measurements.
Sensor data from each input can be read up to ten times per second, with display updates twice each
second. The Model 331 uses current reversal to eliminate thermal EMF errors in resistance sensors.
Standard temperature response curves for silicon diodes, platinum RTDs, and many thermocouples are
included. Up to twenty 200-point CalCurves™ for Lake Shore calibrated sensors or user curves can be
loaded into non-volatile memory via a computer interface or the instrument front panel. A built-in
SoftCal™
storage as user curves.
1
algorithm can also be used to generate curves for silicon diodes and platinum RTDs, for
1
The Lake Shore SoftCal™ algorithm for silicon diode and platinum RTD sensors is a good solution for applications
requiring more accuracy than a standard sensor curve but not in need of traditional calibration. SoftCal uses the
predictability of a standard curve to improve the accuracy of an individual sensor around a few known temperature
reference points. Both versions of the Model 331 can generate SoftCal curves.
Introduction 1-1
A
A
Product Description (Continued)
Lake Shore Model 331 Temperature Controller User’s Manual
Sensor inputs for both versions of the Model 331 are factory configured and compatible with either
diode/RTDs or thermocouple sensors. The purchaser’s choice of two diode/RTD inputs, one diode/RTD
input and one thermocouple input, or two thermocouple inputs must be specified at time of order and
cannot be reconfigured in the field. Software selects appropriate excitation current and signal gain
levels when sensor type is entered via the instrument front panel.
Temperature Control
The Model 331E offers one and the Model 331S offers two proportional-integral-derivative (PID) control
loops. A PID control algorithm calculates control output based on temperature setpoint and feedback
from the control sensor. Wide tuning parameters accommodate most cryogenic cooling systems and
many small high-temperature ovens. Control output is generated by a high-resolution digital-to-analog
converter for smooth continuous control. The user can set the PID values or the Autotuning feature of
the Model 331 can automate the tuning process.
Heater output for Model 331S and Model 331E is a well-regulated variable DC current source. Heater
output is optically isolated from other circuits to reduce interference and ground loops. Heater output
can provide up to 50 W of continuous power to a resistive heater load, and includes two lower ranges
for systems with less cooling power. Heater output is short-circuit protected to prevent instrument
damage if the heater load is accidentally shorted.
The setpoint ramp feature allows smooth continuous changes in setpoint and can also make the
approach to a setpoint temperature more predictable. The zone feature can automatically change
control parameter values for operation over a large temperature range. Values for ten different
temperature zones can be loaded into the instrument, which will select the next appropriate value on
setpoint change.
Interface
The Model 331 is available with both parallel (IEEE-488, 331S only) and serial (RS-232C) computer
interfaces. In addition to data gathering, nearly every function of the instrument can be controlled via
computer interface. Also included is a Model 330 command emulation mode that makes the Model 331
interchangeable with the older Model 330 in software controlled systems.
Each input has a high and low alarm which offer latching and non-latching operation. The two relays on
the Model 331S can be used in conjunction with the alarms to alert the operator of a fault condition or
perform simple on-off control. Relays can be assigned independently to any alarm or be operated
manually.
When not being used for temperature control, the loop 2 control output can be used as an analog
voltage output. It can be configured to send a voltage proportional to temperature to a strip-chart
recorder or data acquisition system. The user may select the scale and data sent to the output,
including temperature, sensor units, or linear equation results. Under manual control, the analog
voltage output can also serve as a voltage source for other applications.
Interface Features of Model 331S and Model 331E
Feature 331S 331E
Numeric keypad
Front panel curve entry
larms
RS-232C interface
IEEE-488 interface
Second control loop
nalog voltage output
Two relays
1-2 Introduction
Lake Shore Model 331 Temperature Controller User’s Manual
Line input assembly
Serial (RS-232C) I/O (DTE)
Heater output
IEEE-488 interface
Terminal block (for relays and analog output)
Sensor input connectors
Figure 1-1. Model 331S Rear Panel Connections
Configurable Display
Both versions of the Model 331 include a bright vacuum fluorescent display that simultaneously
displays up to four readings. Display data includes input and source annunciators for each reading. All
four display locations can be configured by the user. Data from either input may be assigned to any of
the four locations; the user’s choice of temperature, sensor units, maximum, minimum, or linear
equation results can be displayed. Heater range and control output as current or power can also be
continuously displayed for immediate feedback on control operation.
Normal (Default) Display Configuration
The display provides four reading locations. Readings from each input and the control setpoint can be
expressed in any combination of temperature or sensor units, with heater output expressed as a
percent of full scale current or power.
Flexible Configuration
Reading locations can be configured by the user to meet application needs. The character preceding
the reading indicates input A or B or setpoint S. The character following the reading indicates
measurement units or the math function in use.
Curve Entry
The Model 331 display offers the flexibility to support curve, SoftCal™, and zone entry. Curve entry
may be performed accurately and to full resolution via the display and keypad as well as computer
interface.
Introduction 1-3
Lake Shore Model 331 Temperature Controller User’s Manual
1.1 SENSOR SELECTION
Table 1-1. Sensor Temperature Range
Model Useful Range Magnetic Field Use
Diodes Silicon Diode DT-670-SD 1.4 K to 500 K
Silicon Diode DT-670E-BR 30 K to 500 K
Silicon Diode DT-414 1.4 K to 375 K
Silicon Diode DT-421 1.4 K to 325 K
Silicon Diode DT-470-SD 1.4 K to 500 K
Silicon Diode DT-471-SD 10 K to 500 K
GaAlAs Diode TG-120-P 1.4 K to 325 K
GaAlAs Diode TG-120-PL 1.4 K to 325 K
GaAlAs Diode TG-120-SD 1.4 K to 500 K
Positive
Temperature
Coefficient RTDs
100 Ω Platinum
100 Ω Platinum
Rhodium-Iron RF-800-4 1.4 K to 500 K
PT-102/3 14 K to 873 K
PT-111 14 K to 673 K
Rhodium-Iron RF-100T/U 1.4 K to 325 K
Negative
Temperature
Coefficient
RTDs2
Cernox™ CX-1010 2 K to 325 K5
Cernox™ CX-1030-HT 3.5 K to 420 K
Cernox™ CX-1050-HT 4 K to 420 K
Cernox™ CX-1070-HT 15 K to 420 K3
Cernox™ CX-1080-HT 50 K to 420 K3
T ≥ 60 K & B ≤ 3 T
T ≥ 60 K & B ≤ 3 T
T ≥ 60 K & B ≤ 3 T
T ≥ 60 K & B ≤ 3 T
T ≥ 60 K & B ≤ 3 T
T ≥ 60 K & B ≤ 3 T
T > 4.2 K & B ≤ 5 T
T > 4.2 K & B ≤ 5 T
T > 4.2 K & B ≤ 5 T
T > 40 K & B ≤ 2.5 T
T > 40 K & B ≤ 2.5 T
T > 77 K & B ≤ 8 T
T > 77 K & B ≤ 8 T
T > 2 & B ≤ 19 T
3,6
T > 2 & B ≤ 19 T
3,6
T > 2 & B ≤ 19 T
T > 2 & B ≤ 19 T
T > 2 & B ≤ 19 T
Germanium GR-200A/B-1000 2.2 K to 100 K4 Not Recommended
Germanium GR-200A/B-1500 2.6 K to 100 K4 Not Recommended
Germanium GR-200A/B-2500 3.1 K to 100 K4 Not Recommended
Carbon-Glass CGR-1-500 4 K to 325 K5
Carbon-Glass CGR-1-1000 5 K to 325 K5
Carbon-Glass CGR-1-2000 6 K to 325 K5
Rox™ RX-102A 1.4 K to 40 K5
T > 2 K to ≤ 19 T
T > 2 K to ≤ 19 T
T > 2 K to ≤ 19 T
T > 2 K to ≤ 10 T
Thermocouples Type K 9006-006 3.2 K to 1505 K Not Recommended
Type E 9006-004 3.2 K to 934 K Not Recommended
Chromel-AuFe 0.07% 9006-002 1.2 K to 610 K Not Recommended
2
Single excitation current may limit the low temperature range of NTC resistors.
3
Non-HT version maximum temperature: 325 K.
4
Low temperature limited by input resistance range.
5
Low temperature specified with self-heating error: ≤5 mK.
6
Low temperature specified with self-heating error: ≤12 mK.
Silicon diodes are the best choice for general cryogenic use from 1.4 K to above room temperature.
Diodes are economical to use because they follow a standard curve and are interchangeable in many
applications. They are not suitable for use in ionizing radiation or magnetic fields.
Cernox™ thin-film RTDs offer high sensitivity and low magnetic field-induced errors over the 2 K to
420 K temperature range. Cernox sensors require calibration.
Platinum RTDs offer high uniform sensitivity from 30 K to over 800 K. With excellent reproducibility,
they are useful as thermometry standards. They follow a standard curve above 70 K and are
interchangeable in many applications.
1-4 Introduction
Lake Shore Model 331 Temperature Controller User’s Manual
Table 1-2. Typical Sensor Performance
Temperature
Accuracy
Example Lake
Shore Sensor
Silicon Diode DT-670-SD-13
with 1.4H
calibration
Electronic
Accuracy:
Temperature
Equivalents
Temp
Nominal
Resistance/
Voltage
Typical Sensor
Sensitivity
7
Measurement
Resolution:
Temperature
Equivalents
1.4 K 1.644 V -12.49 mV/K 0.8 mK ±13 mK ±25 mK ±1.6 mK
77 K 1.028 V -1.73 mV/K 5.8 mK ±76 mK ±98 mK ±11.6 mK
300 K 0.5597 V -2.3 mV/K 4.4 mK ±47 mK ±79 mK ±8.8 mK
including
Electronic
Accuracy,
CalCurve™, and
Calibrated
500 K 0.0907 V -2.12 mV/K 4.8 mK ±40 mK ±90 mK ±9.6 mK
Silicon Diode DT-470-SD-13
with 1.4H
calibration
1.4 K 1.6981 V -13.1 mV/K 0.8 mK ±13 mK ±25 mK ±1.6 mK
77 K 1.0203 V -1.92 mV/K 5.2 mK ±69 mK ±91 mK ±10.4 mK
300 K 0.5189 V -2.4 mV/K 4.2 mK ±45 mK ±77 mK ±8.4 mK
475 K 0.0906 V -2.22 mV/K 4.6 mK ±39 mK ±89 mK ±9.2 mK
GaAlAs
Diode
TG-120-SD
with 1.4H
calibration
1.4 K 5.391 V -97.5 mV/K 0.2 mK ±7 mK ±19 mK ±0.4 mK
77 K 1.422 V -1.24 mV/K 16.2 mK ±180 mK ±202 mK ±32.4 mK
300 K 0.8978 V -2.85 mV/K 7 mK ±60 mK ±92 mK ±14 mK
475 K 0.3778 V -3.15 mV/K 6.4 mK ±38 mK ±88 mK ±12.8 mK
100 Ω
Platinum
PT-103 with
1.4J calibration
RTD 500 Ω
Full Scale
Cernox™ CX-1050-SD-
HT
9
with 4M
calibration
Germanium GR-200A-1000
with 1.4D
calibration
CarbonGlass
CGR-1-2000
with 4L
calibration
Thermo-
Type K 75 K -5862.9 µV 15.6 µV/K 26 mK ±0.25 K10
couple
50mV
30 K
77 K
300 K
500 K
4.2 K
77 K
300 K
420 K
2 K
4.2 K
10 K
100 K
4.2 K
77 K
300 K
3.660 Ω 0.191 Ω/K
20.38 Ω 0.423 Ω/K
110.35 Ω 0.387 Ω/K
185.668 Ω 0.378 Ω/K
3507.2 Ω -1120.8 Ω/K
205.67 Ω -2.4116 Ω/K
59.467 Ω -0.1727 Ω/K
45.030 Ω -0.0829 Ω/K
6674 Ω -9930 Ω/K
1054 Ω -526 Ω/K
170.9 Ω -38.4 Ω/K
2.257 Ω -0.018 Ω/K
2260 Ω -2060 Ω/K
21.65 Ω -0.157 Ω/K
11.99 Ω -0.015 Ω/K
300 K 1075.3 µV 40.6 µV/K 10 mK ±0.038 K10 ±20 mK
600 K 13325 µV 41.7 µV/K 10 mK ±0.184 K10 ±20 mK
10.5 mK ±23 mK ±33 mK ±21 mK
4.8 mK ±15 mK ±27 mK ±9.6 mK
5.2 mK ±39 mK ±62 mK ±10.4 mK
5.3 mK ±60 mK ±106 mK ±10.6 mK
36 µK ±1.4 mK ±6.4 mK ±72 µK
16.6 mK ±76 mK ±92 mK ±33.2 mK
232 mK ±717 mK ±757 mK ±464 mK
483 mK ±1.42 K ±1.49 K ±966 mK
4 µK ±0.3 mK ±4.3 mK ±8 µK
76 µK ±1 mK ±5 mK ±152 µK
1 mK ±4.4 mK ±9.4 mK ±2 mK
2.22 K ±5.61 K ±5.626 K ±4.44 K
20 µK ±0.5 mK ±4.5 mK ±40 µK
255 mK ±692 mK ±717 mK ±510 mK
2.667 K ±7 K ±7.1 K ±5.344 K
Calibration not
available from
Lake Shore
1505 K 49998.3 µV 36.006 µV/K 12 mK ±0.73 K10 ±24 mK
7
Typical sensor sensitivities were taken from representative calibrations for the sensor listed
8
Control stability of the electronics only, in an ideal thermal system
9
Non-HT version maximum temperature: 325 K
10
Accuracy specification does not include errors from room temperature compensation
Sensor
Electronic
Control
8
Stability
Temperature
:
Equivalents
±52 mK
Introduction 1-5
Lake Shore Model 331 Temperature Controller User’s Manual
1.2 SPECIFICATIONS
Table 1-3. Input Specifications
Diode negative 0 V to 2.5 V 10 µA ±0.05%
PTC RTD positive
NTC RTD negative
Sensor
Temperature
Coefficient
Input Range Excitation Current
negative 0 V to 7.5 V 10 µA ±0.05%
1 mA14
1 mA14
10 µA ±0.05%14
positive
0 Ω to 500 Ω
0 Ω to 5000 Ω
0 Ω to 7500 Ω
12,13
12,13
Thermocouple positive ±25 mV NA 1 µV 0.4 µV ±1 µV ±0.05% of rdg15 ±0.8 µV
positive ±50 mV NA 1 µV 0.4 µV ±1 µV ±0.05% of rdg15 ±0.8 µV
11
Control stability of the electronics only, in an ideal thermal system
12
Current source error has negligible effect on measurement accuracy
13
Diode input excitation can be set to 1 mA – refer to Paragraph 4.4.2
14
Current source error is removed during calibration
15
Accuracy specification does not include errors from room temperature compensation
Display
Resolution
100 µV 10 µV ±80 µV ±0.005% of rdg ±20 µV
100 µV 20 µV ±80 µV ±0.01 % of rdg ±40 µV
10 mΩ 2 mΩ ±0.004 Ω ±0.01% of rdg ±4 mΩ
100 mΩ 20 mΩ ±0.04 Ω ±0.02% of rdg ±40 mΩ
100 mΩ 40 mΩ ±0.1 Ω ±0.04% of rdg ±80 mΩ
Measurement
Resolution
Electronic Accuracy
Electronic
Control
Stability
11
Thermometry
Number of inputs 2
Input configuration Each input is factory configured for either diode/RTD or thermocouples
Isolation Sensor inputs optically isolated from other circuits but not each other
A/D resolution 24-bit
Input accuracy Sensor dependent – refer to Input Specifications table
Measurement resolution Sensor dependent – refer to Input Specifications table
Maximum update rate 10 readings/s on each input (except 5 readings/s on input A when configured
as thermocouple)
User curves Room for twenty 200-point CalCurves™ or user curves
SoftCal™ Improves accuracy of DT-470 diode to ±0.25 K from 30 K to 375 K; improves
accuracy of Platinum RTDs to ±0.25 K from 70 K to 325 K – stored as user
curves
Math Maximum, Minimum, and Linear Equation (Mx + B) or M(x+B)
Filter Averages 2 to 64 input readings
Table 1-4. Sensor Input Configuration
Diode/RTD Thermocouple
Measurement type 4-lead differential 2-lead, room temperature compensated
Excitation
Constant current with current reversal for
RTDs
NA
Diodes: Silicon, GaAlAs RTDs: 100 Ω
Supported sensors
Platinum, 1000 Ω Platinum, Germanium,
Most thermocouple types
Carbon-Glass, Cernox™, and Rox™
Standard curves
DT-470, DT-500D, DT-670, PT-100, PT-
1000, RX-102A, RX-202A
Type E, Type K, Type T, AuFe 0.07%
vs. Cr, AuFe 0.03% vs. Cr
Input connector 6-pin DIN Ceramic isothermal block
1-6 Introduction
Specifications (Continued)
Lake Shore Model 331 Temperature Controller User’s Manual
Control
Control loops Two on 331S, one on 331E
Control type Closed loop digital PID with manual heater output, or open loop
Tuning Autotune (one loop at a time), PID, PID zones
Control stability Sensor dependent – to 2× measurement resolution
(in an ideal thermal system)
PID control parameters
Proportional (gain) 0 to 1000 with 0.1 setting resolution
Integral (reset) 1 to 1000 (1000/s) with 0.1 setting resolution
Derivative (rate) 1 to 200% with 1% resolution
Manual output 0 to 100% with 0.01% setting resolution
Zone control 10 temperature zones with P, I, D, manual heater out, and heater range
Setpoint ramping 0.1 K/min to 100 K/min
Safety limits Curve temperature, power up heater off, short circuit protection
Table 1-5. Heater Output
Loop 1 Loop 2
Heater output type Variable DC current source Variable DC voltage source
Heater output D/A resolution 18-bit 16-bit
Max heater power 50 W 1 W
Max heater output current 1 A 0.1 A
Heater output compliance 50 V 10 V
Heater output ranges 3 decade steps in power 1
Heater load type Resistive Resistive
Heater load range
Heater load for max power
Heater noise (<1 kHz) RMS 50 µV + 0.01% of output voltage <0.3 mV
Isolation
Heater connector Dual banana Detachable terminal block
10 Ω to 100 Ω recommended 100 Ω minimum
50 Ω 100 Ω
Optical isolation between output and
other circuits
None
Table 1-6. Loop 1 Full Scale Heater Power at Typical Resistance
Heater Resistance Heater Range Heater Power
10 Ω
25 Ω
50 Ω
Low
Med
High
Low
Med
High
Low
Med
High
100 mW
1 W
10 W
250 mW
2.5 W
25 W
500 mW
5 W
50 W
Introduction 1-7
Specifications (Continued)
Lake Shore Model 331 Temperature Controller User’s Manual
Front Panel
Display 2 line by 20 character, 9 mm character height, vacuum fluorescent
display
Number of reading displays 1 to 4
Display units K, °C, V, mV, Ω
Reading source Temperature, sensor units, max, min, and linear equation
Display update rate All readings twice per s
Temp display resolution 0.001° from 0° to 99.999°, 0.01° from 100° to 999.99°,
0.1° above 1000°
Sensor units display resolution Sensor dependent to 5 digits
Other displays Setpoint, Heater Range, and Heater Output (user selected)
Setpoint setting resolution Same as display resolution (actual resolution is sensor dependent)
Heater output display Numeric display in percent of full scale for power or current
Heater output resolution 1%
Display annunciators Control Input, Remote, Alarm, Tuning, Ramp, Max, Min, Linear
Keypad 20 full travel keys, numeric and specific functions
Front panel features Front panel curve entry, display brightness control, keypad lock-out
Interface
IEEE-488 interface (331S)
Features SH1, AH1, T5, L4, SR1, RL1, PP0, DC1, DT0, C0, E1
Reading rate To 10 readings per s on each input
Software support LabVIEW™ driver (consult factory for availability)
Serial interface
Electrical format RS-232C
Max baud rate 9600 baud
Connector 9-pin D-sub
Reading rate To 10 readings/s on each input (at 9600 baud)
Special interface features Model 330 command emulation mode
Alarms
Number 4, high and low for each input
Data source Temperature, Sensor Units, Linear Equation
Settings Source, High Setpoint, Low Setpoint, Deadband, Latching or Non-
Latching, Audible On/Off
Actuators Display annunciator, beeper, relays
Relays (331S)
Number 2
Contacts Normally Open (NO), Normally Closed (NC), and Common (C)
Contact rating 30 VDC at 5 A
Operation Activate relays on high, low, or both alarms for either input or manual
Connector Detachable terminal block
Analog voltage output (331S)
Scale User selected
Update rate 10 readings per s
Data source Temperature, Sensor Units, Linear Equation
Settings Input, source, top of scale, bottom of scale, or manual
Range ±10 V
Resolution 0.3 mV
Accuracy ±2.5 mV
Min load resistance 100 Ω (short circuit protected)
1-8 Introduction
Specifications (Continued)
Lake Shore Model 331 Temperature Controller User’s Manual
General
Ambient temperature 15 °C to 35 °C at rated accuracy, 10 °C to 40 °C at reduced accuracy
Power requirement 100, 120, 220, 240 VAC, (+6%, -10%), 50 or 60 Hz, 120 VA
Size 216 mm W × 89 mm H × 368 mm D (8.5 in × 3.5 in × 14.5 in), half rack
Weight 4.8 kg (10.5 lb)
Approval CE mark
Product Configuration
Part Number Description (Input configuration cannot be chang ed in the field)
Standard Temperature Controllers, all features included:
331S Two Diode/Resistor Inputs
331S-T1 One Diode/Resistor, One Thermocouple Input
331S-T2 Two Thermocouple Inputs
Economy Temperature Controllers, all features of the 331S except does not include the following:
IEEE-488, relays, analog voltage output, second control loop.
331E Two Diode/Resistor Inputs
331E-T1 One Diode/Resistor, One Thermocouple Input
331E-T2 Two Thermocouple Inputs
Refer to Chapter 7 of this manual for a complete description of Model 331 options and accessories.
Specifications subject to change without notice.
1.3 SAFETY SUMMARY
Observe these general safety precautions during all phases of instrument operation, service, and
repair. Failure to comply with these precautions or with specific warnings elsewhere in this manual
violates safety standards of design, manufacture, and intended instrument use. Lake Shore
Cryotronics, Inc. assumes no liability for Customer failure to comply with these requirements.
The Model 331 protects the operator and surrounding area from electric shock or burn, mechanical
hazards, excessive temperature, and spread of fire from the instrument. Environmental conditions
outside of the conditions below may pose a hazard to the operator and surrounding area.
• Indoor use.
• Altitude to 2000 meters.
• Temperature for safe operation: 5 °C to 40 °C.
• Maximum relative humidity: 80% for temperature up to 31 °C decreasing linearly to 50% at 40 °C.
• Power supply voltage fluctuations not to exceed ±10% of the nominal voltage.
• Overvoltage category II.
• Pollution degree 2.
Ground The Instrument
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.
The power jack and mating plug of the power cable meet Underwriters Laboratories (UL) and
International Electrotechnical Commission (IEC) safety standards.
Introduction 1-9
Safety Summary (Continued)
Lake Shore Model 331 Temperature Controller User’s Manual
Ventilation
The instrument has ventilation holes in its side covers. Do not block these holes when the instrument is
operating.
Do Not Operate In An Explosive Atmosphere
Do not operate the instrument in the presence of flammable gases or fumes. Operation of any electrical
instrument in such an environment constitutes a definite safety hazard.
Keep Away From Live Circuits
Operating personnel must not remove instrument covers. Refer component replacement and internal
adjustments to qualified maintenance personnel. Do not replace components with power cable
connected. To avoid injuries, always disconnect power and discharge circuits before touching them.
Do Not Substitute Parts Or Modify Instrument
Do not install substitute parts or perform any unauthorized modification to the instrument. Return the
instrument to an authorized Lake Shore Cryotronics, Inc. representative for service and repair to ensure
that safety features are maintained.
Cleaning
Do not submerge instrument. Clean only with a damp cloth and mild detergent. Exterior only.
1.4 SAFETY SYMBOLS
1-10 Introduction
Lake Shore Model 331 Temperature Controller User’s Manual
CHAPTER 2
COOLING SYSTEM DESIGN
2.0 GENERAL
Selecting the proper cryostat or cooling source is probably the most important decision in designing a
temperature control system. The cooling source defines minimum temperature, cool-down time, and
cooling power. (Information on choosing a cooling source is beyond the scope of this manual.) This
chapter provides information on how to get the best temperature measurement and control from cooling
sources with proper setup including sensor and heater installation.
Chapter 2 contains the following major topics. Temperature sensor selection is covered in
Paragraph 2.1. Calibrated sensors are covered in Paragraph 2.2. Sensor installation is covered in
Paragraph 2.3. Heater selection and installation is covered in Paragraph 2.4. Considerations for good
control are covered in Paragraph 2.5. PID Control is covered in Paragraph 2.6. Manual Tuning is
covered in Paragraph 2.7. AutoTuning is covered in Paragraph 2.8. Finally, Zone Tuning is covered in
Paragraph 2.9.
2.1 TEMPERATURE SENSOR SELECTION
This section attempts to answer some of the basic questions concerning temperature sensor selection.
Additional useful information on temperature sensor selection is available in the Lake Shore
Temperature Measurement and Control Catalog. The catalog has a large reference section that
includes sensor characteristics and sensor selection criteria.
2.1.1 Temperature Range
Several important sensor parameters must be considered when choosing a sensor. The first is
temperature range. The experimental temperature range must be known when choosing a sensor.
Some sensors can be damaged by temperatures that are either too high or too low. Manufacturer
recommendations should always be followed.
Sensor sensitivity is also dependent on temperature and can limit the useful range of a sensor. It is
important not to specify a range larger than necessary. If an experiment is being done at liquid helium
temperature, a very high sensitivity is needed for good measurement resolution at that temperature.
That same resolution may not be required to monitor warm up to room temperature. Two different
sensors may be required to tightly cover the range from helium to room temperature, but lowering the
resolution requirement on warm up may allow a less expensive, one sensor solution.
Another thing to consider when choosing a temperature sensor is that instruments like the Model 331
are not able to read some sensors over their entire temperature range. Lake Shore sells calibrated
sensors that operate down to 50 millikelvin (mK), but the Model 331 is limited to above 1 K in its
standard configuration.
2.1.2 Sensor Sensitivity
Temperature sensor sensitivity is a measure of how much a sensor signal changes when the
temperature changes. It is an important sensor characteristic because so many measurement
parameters are related to it. Resolution, accuracy, noise floor, and even control stability depend on
sensitivity. Many sensors have different sensitivities at different temperatures. For example, a
platinum sensor has good sensitivity at higher temperatures but has limited use below 30 kelvin (K)
because its sensitivity drops sharply. It is difficult to determine if a sensor has adequate sensitivity
over the experimental temperature range. This manual has specifications (Table 1-3) that include
sensor sensitivity translated into temperature resolution and accuracy at different points. This is
typical sensor response and can be used as a guide when choosing a sensor to be used with the
Model 331.
Cooling System Design 2-1
Lake Shore Model 331 Temperature Controller User’s Manual
2.1.3 Environmental Conditions
The experimental environment is also important when choosing a sensor. Environmental factors such
as high vacuum, magnetic field, corrosive chemicals, or even radiation can limit the use of some
types of sensors. Lake Shore has devoted much time to developing sensor packages that withstand
the temperatures, vacuum levels, and bonding materials found in typical cryogenic cooling systems.
Experiments done in magnetic fields are becoming very common. Field dependence of temperature
sensors is an important selection criteria for sensors used in these experiments. This manual briefly
qualifies the field dependence of most common sensors in the specifications (Table 1-3). Detailed
field dependence tables are included in the Lake Shore Temperature Measurement and Control
Catalog. When available, specific data on other environmental factors is also included in the catalog.
2.1.4 Measurement Accuracy
Temperature measurements have several sources of error that reduce accuracy. Be sure to account
for errors induced by both the sensor and the instrumentation when computing accuracy. The
instrument has measurement error in reading the sensor signal and error in calculating a temperature
using a temperature response curve. Error results from the sensor being compared to a calibration
standard and the temperature response of a sensor will shift with time and with repeated thermal
cycling (from very cold temperatures to room temperature). Instrument and sensor makers specify
these errors but there are things a user can do to maintain good accuracy. For example, choose a
sensor that has good sensitivity in the most critical temperature range, as sensitivity can minimize the
effect of most error sources. Install the sensor properly following guidelines in Paragraph 2.3. Have
the sensor and instrument periodically recalibrated, or in some other way null the time dependent
errors. Use a sensor calibration that is appropriate for the accuracy requirement.
2.1.5 Sensor Package
Many types of sensors can be purchased in different packages. Some types of sensors can even be
purchased as bare chips; without any package. A sensor package generally determines its size,
thermal and electrical contact to the outside, and sometimes limits temperature range. When different
packages are available for a sensor, the user should consider the mounting surface for the sensor
and how leads will be heat sinked when choosing.
2.2 CALIBRATED SENSORS
There can sometimes be confusion in the difficult task of choosing the right sensor, getting it calibrated,
translating the calibration data into a temperature response curve that the Model 331 can understand,
then getting the curve loaded into the instrument. Lake Shore provides a variety of calibration and curve
loading services to fit different accuracy requirements and budgets.
2.2.1 Traditional Calibration
Calibration is done by comparing a sensor with an unknown temperature response to an accepted
standard. Lake Shore temperature standards are traceable to the U.S. National Institute of Standards
and Testing (NIST) or the National Physical Laboratory in Great Britain. These standards allow Lake
Shore to calibrate sensors from 50 mK to above room temperature. Calibrated sensors are more
expensive than uncalibrated sensors of the same type because of the labor and capitol equipment
used in the process.
This type of calibration provides the most accurate temperature sensors available from Lake Shore.
Errors from sensor calibration are almost always smaller than the error contributed by the Model 331.
The Lake Shore Temperature Measurement and Control Catalog has complete accuracy
specifications for calibrated sensors.
2-2 Cooling System Design
Traditional Calibration (Continued)
Lake Shore Model 331 Temperature Controller User’s Manual
Calibrated sensors include the measured test data printed and plotted, the coefficients of a
Chebychev polynomial that has been fitted to the data, and two tables of data points to be used as
interpolation tables. Both interpolation tables are optimized to allow accurate temperature conversion.
The smaller table, called a breakpoint interpolation table, is sized to fit into instruments like the Model
331 where it is called a temperature response curve. Getting a curve into a Model 331 may require a
CalCurve™ described below or hand entering through the instrument front panel.
It is important to look at instrument specifications before ordering calibrated sensors. A calibrated
sensor is required when a sensor does not follow a standard curve if the user wishes to display in
temperature. Otherwise the Model 331 will operate in sensor units like ohms or volts. The Model 331
may not work over the full temperature range of some sensors. The standard inputs in are limited to
operation above 1 K even with sensors that can be calibrated to 50 mK.
2.2.2 SoftCal™
SoftCal is a good solution for applications that do not require the accuracy of a traditional calibration.
The SoftCal algorithm uses the well behaved nature of sensors that follow a standard curve to
improve the accuracy of individual sensors. A few known temperature points are required to perform
SoftCal.
Lake Shore sells SoftCal calibrated sensors that include both the large interpolation table and the
smaller breakpoint interpolation table. A CalCurve may be required to get the breakpoint table into a
Model 331 where it is called a temperature response curve. Refer to Paragraph 2.2.4.
The Model 331 can also perform a SoftCal calibration. The user must provide one, two, or three
known temperature reference points. The range and accuracy of the calibration is based on these
points. Refer to Paragraph 5.3.
2.2.3 Standard Curves
Some types of sensors behave in a very predictable manner and a standard temperature response
curve can be created for them. Standard curves are a convenient and inexpensive way to get
reasonable temperature accuracy. Sensors that have a standard curve are often used when
interchangeability is important. Some individual sensors are selected for their ability to match a
published standard curve and sold at a premium, but in general these sensors do not provide the
accuracy of a calibrated sensor. For convenience, the Model 331 has several standard curves
included in firmware.
2.2.4 CalCurve™
The CalCurve service provides the user with a convenient way get the temperature response curve
from Lake Shore calibrated sensors into instruments like the Model 331. It can be performed at the
factory when calibrated sensors and instruments are ordered together. The factory installed CalCurve
option is Model 8001-331 and should be ordered with the calibrated sensor. A CalCurve can be done
in the field when additional or replacement sensors are installed. Curve data is loaded into some type
of non-volatile memory that is installed into the instrument by the user. In the case of the Model 331,
the curve is loaded into a non-volatile memory which can be installed into the instrument. The field
installed version is a Model 8002-05-331 and should be ordered with the calibrated sensor.
Customers that have a PC-compatible computer with an RS-232C or IEEE-488 interface have
another option. The Model 8000 is included with the calibrated sensor and can be loaded by the user.
Cooling System Design 2-3
Lake Shore Model 331 Temperature Controller User’s Manual
Regarding accuracy, there are 3
things that can be done with a
temperature sensor:
Lake Shore Silicon Diode
Temperature Sensor
Standard
Standard sensors are interchangeable within published tolerance
bands. Below is a list of Standard
Curve 10 DT-470 Tolerance
(Accuracy) Bands.
BandBand
2 K* -2 K* 100 K100 K
11 ±0.25 K ±0.5 K ±1.0 K
11A ±0.25 K ±1% of Temp.
12 ±0.5 K ±1.0 K ±2.0 K
12A ±0.5 K ±1% of Temp.
13 ±1 K ±1% of Temp.
* Temperatures down to 1.4 K only with
a Precision Calibrated Sensor.
To increase accuracy, perform a
SoftCal with the controller and
sensor. After sensor calibration, the
custom sensor curve replaces the
standard Curve 10.
100 K -100 K -
305 K305 K
305 K -305 K -
375 K375 K
SoftCal
Calibration
A Lake Shore SoftCal applies only to
Silicon Diodes. A 2-point SoftCal
takes data points at 77.35 K and
305 K. A 3-point SoftCal takes data
points at 4.2 K, 77.35 K, and 305 K.
Typical 2-Point AccuracyTypical 2-Point Accuracy
±1.0 K 2 K to <30 K
±0.25 K 30 K to <60 K
±0.15 K 60 K to <345 K
±0.25 K 345 K to <375 K
±1.0 K 375 K to 475 K
Typical 3-Point AccuracyTypical 3-Point Accuracy
±0.5 K 2 K to <30 K
±0.25 K 30 K to <60 K
±0.15 K 60 K to <345 K
±0.25 K 345 K to <375 K
±1.0 K 375 K to 475 K
Enter voltages at the 2 or 3 data
points into SoftCal capable
controllers. A calibration report
comes with the sensor.
Precision
Calibration
Lake Shore precision calibrates
most sensor types by taking up to
99 data points concentrated in
areas of interest. Typical silicon
diode calibration accuracy is listed
below.
Temp. Typical Maximum
<10 K 12 mK 20 mK
10 K 12 mK 20 mK
20 K 15 mK 25 mK
30 K 25 mK 45 mK
50 K 30 mK 55 mK
100 K 25 mK 50 mK
300 K 25 mK 50 mK
340 K 100 mK
480 K 100 mK
A curve is fitted to these points.
A detailed report including Raw
Temperature Data, Polynomial
Fits, and Interpolation Tables
comes with the sensor.
A Precision Option can be
generated for either SoftCal
or the Precision Calibration:
8001-331
Factory installs a NOVRAM
with Precision Option
breakpoint pairs loaded in it.
C-331-2-1.eps
Users download Precision
Option breakpoint pairs in ACSII
format from a floppy disk.
Precision
Option
- or -
8000 8002-05-331
User calculates break-
points and manually enters
data into the controller
Users install a NOVRAM
with Precision Option
breakpoint pairs loaded in it.
Figure 2-1. Silicon Diode Sensor Calibrations and CalCurve
2-4 Cooling System Design
Lake Shore Model 331 Temperature Controller User’s Manual
2.3 SENSOR INSTALLATION
This section highlights some of the important elements of proper sensor installation. For more detailed
information, Lake Shore sensors are shipped with installation instructions that cover that specific sensor
type and package. The Lake Shore Temperature Measurement and Control Catalog includes an
installation section as well. To further help users properly install sensors, Lake Shore offers a line of
Cryogenic Accessories. Many of the materials discussed are available through Lake Shore and can be
ordered with sensors or instruments.
2.3.1 Mounting Materials
Choosing appropriate mounting materials is very important in a cryogenic environment. The high
vacuum used to insulate cryostats is one source of problems. Materials used in these applications
should have a low vapor pressure so they do not evaporate or out-gas and spoil the vacuum
insulation. Metals and ceramics do not have this problem but greases and varnishes must be
checked. Another source of problems is the wide extremes in temperature most sensors are exposed
to. The linear expansion coefficient of a materials becomes important when temperature changes are
so large. Never try to permanently bond materials with linear expansion coefficients that differ by
more than three. A flexible mounting scheme should be used or the parts will break apart, potentially
damaging them. The thermal expansion or contraction of rigid clamps or holders could crush fragile
samples or sensors that do not have the same coefficient. Thermal conductivity is a property of
materials that can change with temperature. Do not assume that a heat sink grease that works well at
room temperature and above will do the same job at low temperatures.
2.3.2 Sensor Location
Finding a good place to mount a sensor in an already crowded cryostat is never easy. There are less
problems if the entire load and sample holder are at the same temperature. Unfortunately, this not the
case in many systems. Temperature gradients (differences in temperature) exist because there is
seldom perfect balance between the cooling source and heat sources. Even in a well-controlled
system, unwanted heat sources like thermal radiation and heat conducting through mounting
structures can cause gradients. For best accuracy, sensors should be positioned near the sample, so
that little or no heat flows between the sample and sensor. This may not, however, be the best
location for temperature control as discussed below.
2.3.3 Thermal Conductivity
The ability of heat to flow through a material is called thermal conductivity. Good thermal conductivity
is important in any part of a cryogenic system that is intended to be the same temperature. Copper
and aluminum are examples of metals that have good thermal conductivity, while stainless steel does
not. Non-metallic, electrically-insulating materials like alumina oxide and similar ceramics have good
thermal conductivity, while G-10 epoxy-impregnated fiberglass does not. Sensor packages, cooling
loads, and sample holders should have good thermal conductivity to reduce temperature gradients.
Surprisingly, the connections between thermally conductive mounting surfaces often have very poor
thermal conductivity.
2.3.4 Contact Area
Thermal contact area greatly affects thermal conduction because a larger area has more opportunity
to transfer heat. Even when the size of a sensor package is fixed, thermal contact area can be
improved with the use of a gasket material. A soft gasket material forms into the rough mating surface
to increase the area of the two surfaces that are in contact. Good gasket materials are soft, thin, and
have good thermal conductivity. They must also withstand the environmental extremes. Indium foil
and cryogenic grease are good examples.
Cooling System Design 2-5
Lake Shore Model 331 Temperature Controller User’s Manual
2.3.5 Contact Pressure
When sensors are permanently mounted, the solder or epoxy used to hold the sensor act as both
gasket and adhesive. Permanent mounting is not a good solution for everyone because it limits
flexibility and can potentially damage sensors. Much care should be taken not to over heat or
mechanically stress sensor packages. Less permanent mountings require some pressure to hold the
sensor to its mounting surface. Pressure greatly improves the action of gasket material to increase
thermal conductivity and reduce thermal gradients. A spring clamp is recommended so that different
rates of thermal expansion do not increase or decrease pressure with temperature change.
2.3.6 Lead Wire
Different types of sensors come with different types and lengths of electrical leads. In general a
significant length of lead wire must be added to the sensor for proper heat sinking and connecting to
a bulk head connector at the vacuum boundary. The lead wire must be a good electrical conductor,
but should not be a good thermal conductor, or heat will transfer down the leads and change the
temperature reading of the sensor. Small 30 to 40 AWG wire made of an alloy like phosphor bronze is
much better than copper wire. Thin wire insulation is preferred and twisted wire should be used to
reduce the effect of RF noise if it is present. The wire used on the room temperature side of the
vacuum boundary is not critical so copper cable is normally used.
Vacuum Shroud
To Room
Temperature
Refrigerator
Expander
Vacuum Space
Radiation Shield
Dental Floss
Tie-Down
Therm al Anchor
(Bobbin)
-or-
Cryogenic Tape
Refrigerator
Stage
Second
Thermal Anchor
Cryogenic Wire
diameter,
(small
(Bobbin)
large AWG)
Cold Stage and
Sensor
Sample Holder
Drawing
Not To Scale
Optical Window
Heater
(wiring not shown
for clarity)
(If Required)
P-331-2-2.bmp
Figure 2-2. Typical Sensor Installation In A Mechanical Refrigerator
2-6 Cooling System Design
Lake Shore Model 331 Temperature Controller User’s Manual
2.3.7 Lead Soldering
When additional wire is soldered to short sensor leads, care must be taken not to overheat the
sensor. A heat sink such as a metal wire clamp or alligator clip will heat sink the leads and protect the
sensor. Leads should be tinned before bonding to reduce the time that heat is applied to the sensor
lead. Solder flux should be cleaned after soldering to prevent corrosion.
2.3.8 Heat Sinking Leads
Sensor leads can be a significant source of error if they are not properly heat sinked. Heat will
transfer down even small leads and alter the sensor reading. The goal of heat sinking is to cool the
leads to a temperature as close to the sensor as possible. This can be accomplished by putting a
significant length of lead wire in thermal contact with every cooled surface between room temperature
and the sensor. Lead wires can be adhered to cold surfaces with varnish over a thin electrical
insulator like cigarette paper. They can also be wound onto a bobbin that is firmly attached to the cold
surface. Some sensor packages include a heat sink bobbin and wrapped lead wires to simplify heat
sinking.
2.3.9 Thermal Radiation
Thermal (black body) radiation is one of the ways heat is transferred. Warm surfaces radiate heat to
cold surfaces even through a vacuum. The difference in temperature between the surfaces is one
thing that determines how much heat is transferred. Thermal radiation causes thermal gradients and
reduces measurement accuracy. Many cooling systems include a radiation shield. The purpose of the
shield is to surround the load, sample, and sensor with a surface that is at or near their temperature
to minimize radiation. The shield is exposed to the room temperature surface of the vacuum shroud
on its outer surface, so some cooling power must be directed to the shield to keep it near the load
temperature. If the cooling system does not include an integrated radiation shield (or one cannot be
easily made), one alternative is to wrap several layers of super-insulation (aluminized Mylar) loosely
between the vacuum shroud and load. This reduces radiation transfer to the sample space.
2.4 HEATER SELECTION AND INSTALLATION
There is a variety of resistive heaters that can be used as the controlled heating source for temperature
control. The mostly metal alloys like nichrome are usually wire or foil. Shapes and sizes vary to permit
installation into different systems.
2.4.1 Heater Resistance and Power
Cryogenic cooling systems have a wide range of cooling power. The resistive heater must be able to
provide sufficient heating power to warm the system. The Model 331 can supply up to 50 W of power
to a heater (if the heater resistance is appropriate). The Model 331 heater output current source has a
maximum output of 1 A, limiting maximum power to:
Max Power (watts) = (1 ampere)2 × Resistance (ohms).
Even though the Model 331 output is a current source, it has a voltage limit (called the compliance
voltage) of 50 V, which also limits maximum power:
Max Power (watts)
(50 volts)
=
Resistance (ohms)
2
.
Both limits are in place at the same time, so the smallest of the two computations gives the maximum
power available to the heater. A heater of 50 Ω allows the instrument to provide its maximum power
of 50 watts. A typical smaller resistance of 25 Ω allows 25 watts of power, while a typical larger
resistance of 100 Ω is limited by compliance voltage to 25 watts. The resistor chosen as a heater
must be able to withstand the power being dissipated in it. Pre-packaged resistors have a power
specification that is usually given for the resistor in free air. This power may need to be derated if
used in a vacuum where convection cooling can not take place and it is not adequately heat sinked to
a cooled surface.
Cooling System Design 2-7
2.4.2 Heater Location
For best temperature measurement accuracy the heater should be located so that heat flow between
the cooling power and heater is minimized. For best control the heater should be in close thermal
contact with the cooling power. Geometry of the load can make one or both of these difficult to
achieve. That is why there are several heater shapes and sizes.
2.4.3 Heater Types
Resistive wire like nichrome is the most flexible type of heater available. The wire can be purchased
with electrical insulation and has a predictable resistance per given length. This type of heater wire
can be wrapped around a cooling load to give balanced, even heating of the area. Similar to sensor
lead wire, the entire length of the heater wire should be in good thermal contact with the load to allow
for thermal transfer. Heat sinking also protects the wire from over heating and burning out.
Resistive heater wire is also wound into cartridge heaters. Cartridge heaters are more convenient but
are bulky and more difficult to place on small loads. A typical cartridge is 1/4 inch in diameter and
1 inch long. The cartridge should be snugly held in a hole in the load or clamped to a flat surface.
Heat sinking for good thermal contact is again important.
Foil heaters are thin layers of resistive material adhered to, or screened on to, electrically insulating
sheets. There are a variety of shapes and sizes. The proper size heater can evenly heat a flat surface
or around a round load. The entire active area should be in good thermal contact with the load, not
only for maximum heating effect, but to keep spots in the heater from over heating and burning out.
Lake Shore Model 331 Temperature Controller User’s Manual
2.4.4 Heater Wiring
When wiring inside a vacuum shroud, we recommend using 30 AWG copper wire for heater leads.
Too much heat can leak in when larger wire is used. Heat sinking, similar to that used for the sensor
leads, should be included so that any heat leaking in does not warm the load when the heater is not
running. The lead wires should be twisted to minimize noise coupling between the heater and other
leads in the system. When wiring outside the vacuum shroud, larger gage copper cable can be used,
and twisting is still recommended.
2.5 CONSIDERATION FOR GOOD CONTROL
Most of the techniques discussed above to improve cryogenic temperature accuracy apply to control
as well. There is an obvious exception in sensor location. A compromise is suggested below in
Paragraph 2.5.3 – Two Sensor Approach.
2.5.1 Thermal Conductivity
Good thermal conductivity is important in any part of a cryogenic system that is intended to be at the
same temperature. Most systems begin with materials that have good conductivity themselves, but as
sensors, heaters, sample holders, etc., are added to an ever more crowded space, the junctions
between parts are often overlooked. In order for control to work well, junctions between the elements
of the control loop must be in close thermal contact and have good thermal conductivity. Gasket
materials should always be used along with reasonable pressure.
2.5.2 Thermal Lag
Poor thermal conductivity causes thermal gradients that reduce accuracy and also cause thermal lag
that make it difficult for controllers to do their job. Thermal lag is the time it takes for a change in
heating or cooling power to propagate through the load and get to the feedback sensor. Because the
feedback sensor is the only thing that lets the controller know what is happening in the system, slow
information to the sensor slows the response time. For example, if the temperature at the load drops
slightly below the setpoint, the controller gradually increases heating power. If the feedback
information is slow, the controller puts too much heat into the system before it is told to reduce heat.
The excess heat causes a temperature overshoot, which degrades control stability. The best way to
improve thermal lag is to pay close attention to thermal conductivity both in the parts used and their
junctions.
2-8 Cooling System Design
2.5.3 Two-Sensor Approach
There is a conflict between the best sensor location for measurement accuracy and the best sensor
location for control. For measurement accuracy the sensor should be very near the sample being
measured which is away from the heating and cooling sources to reduce heat flow across the sample
and thermal gradients. The best control stability is achieved when the feedback sensor is near both
the heater and cooling source to reduce thermal lag. If both control stability and measurement
accuracy are critical it may be necessary to use two sensors, one for each function. Many
temperature controllers including the Model 331 have two sensor inputs for this reason.
2.5.4 Thermal Mass
Cryogenic designers understandably want to keep the thermal mass of the load as small as possible
so the system can cool quickly and improve cycle time. Small mass can also have the advantage of
reduced thermal gradients. Controlling a very small mass is difficult because there is no buffer to
adsorb small changes in the system. Without buffering, small disturbances can very quickly create
large temperature changes. In some systems it is necessary to add a small amount of thermal mass
such as a copper block in order to improve control stability.
2.5.5 System Nonlinearity
Because of nonlinearities in the control system, a system controlling well at one temperature may not
control well at another temperature. While nonlinearities exist in all temperature control systems, they
are most evident at cryogenic temperatures. When the operating temperature changes the behavior
of the control loop, the controller must be retuned. As an example, a thermal mass acts differently at
different temperatures. The specific heat of the load material is a major factor in thermal mass and
the specific heat of materials like copper change as much as three orders of magnitude when cooled
from 100 K to 10 K. Changes in cooling power and sensor sensitivity are also sources of nonlinearity.
The cooling power of most cooling sources also changes with load temperature. This is very
important when operating at temperatures near the highest or lowest temperature that a system can
reach. Nonlinearities within a few degrees of these high and low temperatures make it very difficult to
configure them for stable control. If difficulty is encountered, it is recommended to gain experience
with the system at temperatures several degrees away from the limit and gradually approach it in
small steps.
Keep an eye on temperature sensitivity. Sensitivity not only affects control stability but it also
contributes to the overall control system gain. The large changes in sensitivity that make some
sensors so useful may make it necessary to retune the control loop more often.
Lake Shore Model 331 Temperature Controller User’s Manual
2.6 PID CONTROL
For closed-loop operation, the Model 331 temperature controller uses a algorithm called PID control.
The control equation for the PID algorithm has three variable terms: proportional (P), integral (I), and
derivative (D). See Figure 2-3. Changing these variables for best control of a system is called tuning.
The PID equation in the Model 331 is:
Heater Output =+ +
where the error (e) is defined as: e = Setpoint – Feedback Reading.
Proportional is discussed in Paragraph 2.6.1. Integral is discussed in Paragraph 2.6.2. Derivative is
discussed in Paragraph 2.6.3. Finally, the manual heater output is discussed in Paragraph 2.6.4.
Cooling System Design 2-9
L
Pe I edt D
M
N
z
af
de
dt
O
P
Q
2.6.1 Proportional (P)
The Proportional term, also called gain, must have a value greater than zero for the control loop to
operate. The value of the proportional term is multiplied by the error (e) which is defined as the
difference between the setpoint and feedback temperatures, to generate the proportional contribution
to the output: Output (P) = Pe. If proportional is acting alone, with no integral, there must always be
an error or the output will go to zero. A great deal must be known about the load, sensor, and
controller to compute a proportional setting (P). Most often, the proportional setting is determined by
trial and error. The proportional setting is part of the overall control loop gain, and so are the heater
range and cooling power. The proportional setting will need to change if either of these change.
2.6.2 Integral (I)
In the control loop, the integral term, also called reset, looks at error over time to build the integral
contribution to the output:
Output I PI e dt
=
af a f
By adding the integral to proportional contributions, the error that is necessary in a proportional only
system can be eliminated. When the error is at zero, controlling at the setpoint, the output is held
constant by the integral contribution. The integral setting (I) is more predictable than the gain setting.
It is related to the dominant time constant of the load. As discussed in Paragraph 2.7.3, measuring
this time constant allows a reasonable calculation of the integral setting. In the Model 331, the integral
term is not set in seconds like some other systems. The integral setting can be derived by dividing
1000 by the integral seconds: I
Lake Shore Model 331 Temperature Controller User’s Manual
z
.
setting
= 1000 / I
seconds
.
2.6.3 Derivative (D)
The derivative term, also called rate, acts on the change in error with time to make its contribution to
the output:
Output D PD
()= .
de
dt
By reacting to a fast changing error signal the derivative can work to boost the output when the
setpoint changes quickly, reducing the time it takes for temperature to reach the setpoint. It can also
see the error decreasing rapidly when the temperature nears the setpoint and reduce the output for
less overshoot. The derivative term can be useful in fast changing systems but it is often turned off
during steady state control because it reacts too strongly to small disturbances. The derivative setting
(D) is related to the dominant time constant of the load similar to the I
proportional to I
when used.
setting
2.6.4 Manual Heater Power (MHP) Output
The Model 331 has a control setting that is not a normal part of a PID control loop. Manual Heater
Power (MHP) output can be used for open loop control, meaning feedback is ignored and the heater
output stays at the users manual setting. This is a good way to put constant heating power into a load
when needed. The MHP output term can also be added to the PID output. Some users prefer to set a
power near that necessary to control at a setpoint and let the closed loop make up the small
difference. MHP output is set in percent of full scale current or power for a given heater range.
NOTE: MHP output should be set to 0% when not in use.
and is therefore set
setting
2-10 Cooling System Design
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