Isotech microK-400, micro-800 User Manual

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User Manual

Applies to:

Software version 1.4.16+

Firmware version 3.17+

Isothermal Technology Limited

Pine Grove

Southport

Merseyside

PR9 9AG

T: +44 (0)1704 543830

F: +44 (0)1701 544799

E: info@microk.co.uk

W: www.microk.co.uk

CONTENTS

1 INTRODUCTION ............................................................................... 6

1.1 Unpacking ............................................................................................................................. 7

1.2 Safety ..................................................................................................................................... 7

1.3 Powering Up Your microK ................................................................................................. 9

1.4 A Quick Tour of Your microK ........................................................................................... 9

2 MAKING A MEASUREMENT (TUTORIALS) .................................. 12

2.1 Measuring Temperature with a Calibrated SPRT .......................................................... 12

2.2 Measuring Temperature with a Thermocouple .............................................................. 16

3 DRIVING YOUR MICROK ............................................................... 20

3.1 Introduction ........................................................................................................................ 20

3.2 The Startup Window ......................................................................................................... 20

3.3 The Main Window ............................................................................................................. 21

3.4 The Single Tab.................................................................................................................... 22

3.5 The Multi Tab .................................................................................................................... 25

3.6 The Settings Tab ................................................................................................................ 26

3.7 The Instrument Tab ........................................................................................................... 31

3.7.1 Edit Thermometers ........................................................................ 31

3.7.2 Edit Resistors ................................................................................ 34

3.7.3 Calibration .................................................................................... 35

3.7.4 Restart Software ............................................................................ 35

3.7.5 Update Software............................................................................ 36

3.7.6 Change Password .......................................................................... 36

3.7.7 Port Settings .................................................................................. 37

3.7.8 Set Date and Time ......................................................................... 38

3.7.9 Backup Data.................................................................................. 38

3.7.10 Clear Data Files ......................................................................... 39

3.7.11 Backup Configuration ............................................................... 39

3.7.12 Load Configuration ................................................................... 39

3.8 Using the Thermometer Database .................................................................................... 40

3.9 Using the Reference Resistors Database .......................................................................... 41

3.10 Saving Instrument Configurations .............................................................................. 41

3.11 Password Protection of Key Settings ........................................................................... 42

4 CONNECTING THERMOMETER SENSORS ................................. 43

4.1 The “Cable-Pod” Connectors ........................................................................................... 43

4.2 Connecting PRTs (4-wire) ................................................................................................. 43

4.3 Connecting PRTs (3-wire) ................................................................................................. 44

4.4 Connecting PRTs (2-wire) ................................................................................................. 44

4.5 Connecting Thermocouples (external Ice Point or WTP) .............................................. 45

4.6 Connecting Thermocouples (using RJ compensation) ................................................... 46

4.7 Connecting Thermistors .................................................................................................... 46

5 GOOD PRACTICE GUIDELINES .................................................... 48

5.1 Looking After Your microK ............................................................................................. 48

5.2 Making a Good Electrical Measurement ......................................................................... 48

6 THE MICROK TECHNOLOGY ........................................................ 51

6.1 The ADC ............................................................................................................................. 51

6.2 Substitution Topology ....................................................................................................... 53

6.3 Minimising Thermal EMFs .............................................................................................. 55

6.4 Solid-State Switching ......................................................................................................... 56

6.5 Inherent Stability ............................................................................................................... 56

6.6 Eliminating Self-Heating Effects ...................................................................................... 57

7 CALIBRATION ................................................................................ 58

7.1 Checking Calibration ........................................................................................................ 58

7.1.1 Checking the Master Current Source ..............................................58

7.1.2 Resistance Measurements ..............................................................59

7.1.2.1 Zero Ohms Check ..................................................................59

7.1.2.2 400 Ω Internal Reference Resistor..........................................60

7.1.2.3 100 Ω Internal Reference Resistor..........................................61

7.1.2.4 25 Ω Internal Reference Resistor ...........................................61

7.1.2.5 10 Ω Internal Reference Resistor ...........................................61

7.1.2.6 1 Ω Internal Reference Resistor .............................................61

7.1.3 Voltage Measurements ..................................................................62

7.1.3.1 Zero Voltage Offsets ..............................................................62

7.1.3.2 Voltage Span Check ...............................................................62

7.2 Adjusting Calibration ........................................................................................................ 63

7.2.1 Calibrate Master Current Source ....................................................64

7.2.2 Calibrating the 400 Ω Internal Reference Resistor .........................65

7.2.3 Calibrating the 100 Ω Internal Reference Resistor ......................... 66

7.2.4 Calibrating the 25 Ω Internal Reference Resistor ........................... 66

7.2.5 Calibrating the 10 Ω Internal Reference Resistor ........................... 66

7.2.6 Calibrating the 1 Ω Internal Reference Resistor ............................. 66

7.2.7 Calibrating Voltage Zeros ............................................................. 67

7.2.8 Calibrating Voltage Span .............................................................. 68

8 RS232 INTERFACE ........................................................................ 70

8.1 Establishing an RS232 Connection ................................................................................... 70

9 GPIB ................................................................................................ 73

9.1 GPIB Address ..................................................................................................................... 74

9.2 Establishing a GPIB Connection ...................................................................................... 74

10 SCPI COMMAND SET .................................................................... 75

10.1 Command Terminators ................................................................................................ 75

10.2 SCPI Command Structure ........................................................................................... 75

10.2.1 SCPI Numeric Suffices.............................................................. 77

10.2.2 Parameters ................................................................................. 77

10.2.3 Units ......................................................................................... 77

10.3 Making Measurements using SCPI Commands ......................................................... 79

10.3.1 Measuring Resistance using SCPI Commands ........................... 79

10.3.2 Measuring Voltage using SCPI Commands ............................... 80

10.4 SCPI Commands ........................................................................................................... 81

10.4.1 Command: *IDN? ..................................................................... 82

10.4.2 Command: *RST ....................................................................... 82

10.4.3 Command: SENSe:FUNCtion ................................................... 82

10.4.4 Command: SENSe:FUNCtion? ................................................. 82

10.4.5 Command: SENSe:CHANnel .................................................... 83

10.4.6 Command: SENSe:CHANnel? .................................................. 83

10.4.7 Command: SENSe:VOLTage:RANGe ...................................... 83

10.4.8 Command: SENSe:VOLTage:RANGe? .................................... 84

10.4.9 Command: SENSe:FRESistance:REFerence ............................. 84

10.4.10 Command: SENSe:FRESistance:REFerence? ............................ 84

10.4.11 Command: SENSe:FRESistance:RANGe .................................. 84

10.4.12 Command: SENSe:FRESistance:RANGe? ................................ 85

10.4.13 Command: SENSe:RATio:REFerence ....................................... 85

10.4.14 Command: SENSe:RATio:REFerence? ..................................... 85

10.4.15 Command: SENSe:RATio:RANGe ........................................... 86

10.4.16 Command: SENSe:RATio:RANGe? ......................................... 86

10.4.17 Command: INITiate .................................................................. 87

10.4.18 Command: FETCh? ................................................................... 87

10.4.19 Command: READ? ................................................................... 87

10.4.20 Command: READ#? ................................................................. 87

10.4.21 Command: MEASure:VOLTage? ..............................................88

10.4.22 Command: MEASure:FRES:REF? ............................................88

10.4.23 Command: MEASure:RAT:REF? ..............................................89

10.4.24 Command: CURRent .................................................................89

10.4.25 Command: TEST:CURRent .......................................................90

10.4.26 Command: CALibrate:CURRent ...............................................90

10.4.27 Command: CALibrate:REFerence .............................................90

10.4.28 Command: CALibrate:REFerence? ............................................90

10.4.29 Command: CALibrate:OFFSet ...................................................91

10.4.30 Command: CALibrate:OFFSet? .................................................91

10.4.31 Command: CALibrate:GAIN .....................................................91

10.4.32 Command: CALibrate:GAIN? ...................................................92

10.4.33 Command: CALibrate:PASSword .............................................92

10.4.34 Command: CALibrate:UNLock .................................................92

10.4.35 Command: CALibrate:LOCK ....................................................93

11 SPECIFICATION ............................................................................. 94

12 APPROVALS .................................................................................. 96

12.1 CE Declaration .............................................................................................................. 96

12.2 FCC Statement .............................................................................................................. 96

12.3 Standards Applied ........................................................................................................ 97

1 Introduction

The microK-400 and micro-800 are the only precision thermometry instruments

that can achieve sub mK precision and will work with all three common

thermometer sensors (PRTs, Thermocouples and Thermistors). They are based

on a completely new measurement technology, unique to these products, that

provides better accuracy and lower noise than comparables technologies (see

section 6). They are also the first instruments of their type to be completely solid-

state, making them highly reliable.

Despite their sophistication, these instruments are very easy to use. There are no

knobs and dials, just a colour touch screen that makes use of the familiar

Windows CE™ operating system. If you use a Windows™ operating system on

your PC, you will find these instruments intuitive and easy to use. The USB port

on the front panel allows you to plug in and use other devices that work with

Windows CE™ such as a mouse, keyboard or flash drive.

Readings can be displayed in resistance ratio, ohms, volts or temperature units

(°C, °F or K). Algorithms for conversion to temperature include:

PRTs: ITS-90

Callendar-Van Dusen (IEC751 or custom

coefficients)

Thermocouples: IEC584-1 (for type B, E, J, K, N, R, S, T)

Type L polynomial

Gold Platinum Reference Function Polynomial

Thermistor: Steinhart-Hart

This manual provides a comprehensive guide to using the instrument. We

recognise that you will probably not wish to read it through at this time so

suggest you read the safety section below, take one of the tutorials in section 2

and then refer back to the manual using the list of contents to find additional

information as required.

1.1 Unpacking

Your microK product should comprise the following items:

 microK precision thermometer  power lead suitable for your country  this user manual

If any item is missing or damaged, please report this immediately to your

supplier. If possible, we recommend that you retain the packaging material in

case you need to return the instrument for calibration or service since it has been

designed to ensure that your microK is properly protected during transportation.

1.2 Safety

The microK is a precision instrument, designed for use in a laboratory. It

complies with the requirements of safety standard EN61010-1 (2001) and is

therefore safe to use in laboratory or light industrial environments. It is not

intended for use outdoors or in extreme environments (refer to specification in

Section 11).

The microK is likely to be connected to thermometer sensors in use and the

operator should take care to ensure that the complete system is safe. For

example, metal sheathed thermometers may be connected to the microK and then

placed in a furnace powered from a 230V electrical supply. Single fault

conditions in such a furnace could lead to the thermometer wires and therefore

the front terminals of the microK becoming electrically live and therefore a

hazard to the operator. Suitable precautions should be taken, such as using an

isolating transformer in the supply to such a furnace. If you require further advice

on safety issues, please contact Isothermal Technology or one of our appointed

distributors - we have extensive experience of thermometry and can provide

advice and equipment to help you.

Retain these instructions. Use only as specified in these operating instructions or

the intrinsic protection may be impaired.

Please observe the following safety precautions:

 Do not use your microK if it is damaged  Only connect to an earthed supply socket. THIS UNIT IS CLASS 1

CONSTRUCTION AND MUST BE EARTHED!

 Connect only to a power supply with a voltage corresponding to that on

the rating plate

 This equipment is for indoor use and will meet its performance figures

within an ambient temperature range of 5°C to 40°C with maximum relative humidity of 80% for temperatures up to 31ºC decreasing linearly to 50% RH at 40ºC

 Equipment is for operation at installation category II (transient voltages)

and pollution degree ll in accordance with IEC 664 at altitudes up to 2000 metres

 Before replacing a fuse, DISCONNECT THE EQUIPMENT FROM THE

ELECTRICAL SUPPLY

 The fuse is contained in the IEC socket on the rear panel. It must only be

replaced with a fuse of the type and rating marked on the rear panel

 If a replacement fuse fails immediately, contact your local service agent.

DO NOT replace with a higher value

 Always use the power cord supplied. Your sales outlet can provide a lead

suitable for your country

 This equipment is for use in moderate climates only. NEVER use the

equipment in damp or wet conditions

 Avoid excessive heat, humidity, dust & vibration  Do not place liquid filled containers on the equipment  Do not use where the equipment (or any associated accessories) may be

subjected to dripping or splashing liquids

 Ensure that the power switch is easily accessible to allow the unit to be

switched off

 The equipment weighs 13kg; use the handles provided. Always

disconnect the equipment from the electrical supply and any ancillary units before moving

 Ensure that tabletop equipment is placed on a solid, level surface, which

is able to support its weight (and that of any attached accessories)

 Ensure all cables and wires are routed safely to avoid tripping: also to

avoid sharp bends and pinches

 Clean only with a damp cloth. Do not wet or allow moisture to penetrate

the unit. Do not use solvents. See section 5.1 for details of cleaning procedure

 The product should be subjected to regular in-service inspections as

required by local regulations; a yearly interval is suggested

 Verify that the supply cordset is undamaged and that the enclosure is

bonded to protective earth. Do not apply earth test currents to any front panel terminal nor to the shrouds of the USB, RS232 or GPIB connectors

 The product is designed to comply with EN 61010-1 and can be flash

tested. It is fitted with radio frequency interference suppressors. Therefore it is recommended that only a D.C. test be performed. Performing flash tests repeatedly can damage insulation

 This equipment contains no user-serviceable parts. Refer all repairs to

qualified service personnel. Contact Isothermal Technology or one of our appointed distributors for details of approved service outlets

1.3 Powering Up Your microK

The microK operates on any standard AC electrical supply (88-264V RMS at 47-

63Hz) so unless your supply is unusual you can simply use the power cord

provided to connect your microK to a suitable electrical outlet.

The power switch is located at the rear of the instrument, immediately below the

IEC connector. When you turn your microK on it will go through a standard

Windows CE™ boot sequence and then display a Window containing the

Resume button. Pressing Resume restarts the microK in the configuration it was

in prior to the last power down, you will then see the Main Window and be ready

to operate your instrument.

Before pressing the Resume button, make sure that any thermometers attached

will not be damaged by the sense currents that will be applied (the last values

used). If there is a problem, disconnect your sensors before proceeding and then

reconnect them after changing the sense current to the required values.

1.4 A Quick Tour of Your microK

On the front panel of your microK you will find the input terminals for the three

measurement channels, the touch screen/colour display and a USB connector:

USB

Input

Terminals

Touch Screen

& Display

Connector

Input Terminals: The input terminals accept 4mm plugs, spades or bare wires.

The current (I) and voltage sense (V) terminals are spaced on ¾” centres so that

standard BNC to 4mm adaptors (not supplied) can be used to connect to

thermometer sensors that have BNC terminations.

The contact material for the connectors is gold plated tellurium-copper, offering

extremely low thermal EMFs when connected to copper wires/connectors. This

is essential when using precision thermocouples.

Display: The display is a colour TFT VGA (640 x 480) LCD with a long-life

CCFL (cold-cathode fluorescent lamp) backlight. A touch panel is mounted in

front of the display so that you can control the instrument by simply touching the

buttons displayed on the LCD. The touch panel is an industrial grade components

offering good durability. It is intended to be operated with a finger. A stylus

intended for PDAs may also be used – never use a sharp object with the touch

panel as this will lead to premature failure.

The USB Connector: The USB connector is primarily intended to allow you to

connect a USB flash drive, store measurement results and transfer these to a PC.

The flash drive may also be used to backup the databases of thermometers,

reference resistors and instrument configurations for your microK.

Connector

(unused)

GPIB

Connector

Other USB devices such as a mouse, keyboard, keypad or USB hub may be

connected to the USB port and used, provided they utilise the standard class

drivers provided with the Windows CE™ operating system incorporated in your

microK.

On the rear panel of your microK you will find the electrical supply

connector/power switch/fuse module plus the interface connectors that allow you

to connect your instrument to a PC. The RS232 and GPIB ports allow you to

control the instrument and take measurements from a PC with your own software

(see section 8). The command protocol employs the widely used SCPI format

(see section 9 for details). The USB connector is provided for future expansion

and should not be used on this model.

IEC 60320-1

Power Connector

On/Off

Switch

Supply Fuse

USB-B Connector

RS232

2 Making a Measurement (Tutorials)

The operator interface is powered by the Windows CE™ operating system. With

the widespread use of Windows applications on PCs, driving your microK should

be fairly intuitive. As with most Windows™ applications, it is possible to

navigate your way through a process using a number of different paths, so rather

than describe each window and the function of each button and then leaving you

to work out how to operate the instrument, we provide you with a number of

tutorials that illustrate common applications. Even if these do not describe your

application, it is worth working through one of them since it will provide you

with a broad understanding of the wide range of features available on your

microK.

A traditional description of the function of all the features provided by the

operator interface is given in section 3.

2.1 Measuring Temperature with a Calibrated SPRT

From startup, press Resume to restart your microK:

Before making any measurement, you will have to enter information about the

thermometer into the microK’s database. When the main window opens, press

the Instrument tab:

In the Instrument tab, press Edit Thermometers:

You will be prompted to enter the password (set to “1234” initially, but this

should be changed before using the microK in a real measurement/calibration

application to ensure security – see section 3.7.6). Enter the password to open the

thermometer database window. Press New to create a new thermometer entry in

the database and enter data by pressing the up/down or ellipses buttons by each

field:

Press Coefficients to open the coefficients window. Press the ellipses buttons to

enter the calibration data for the thermometer from its calibration certificate:

Press OK to close the coefficients window and press OK again to close the

thermometer database window.

Press the Settings tab in the main window and disable channels 2 and 3 (this will

speed up measurements on channel 1, which we will be using) by using the

up/down buttons by the Channel box to select these channels and pressing

Disable. Use the up/down buttons to return to channel 1. Use the up/down (or

ellipses) buttons by each box to select the required settings:

The sense current is assumed to be 1mA in this tutorial. It can be set to other

values using the ellipses button by the Current mA box (see section 3.6).

Connect the SPRT to channel 1 (see section 4.2 for details on how to connect 4-

wire PRTs). The tutorial assumes you are using the internal 100Ω reference

resistor. To use an external reference resistor, first enter information on the

resistor into the microK’s database (see section 3.7.2), then in the Settings tab

select the channel to which the reference is connected in the Reference Channel

box and the reference resistor entry in the Reference Resistor box.

Press the Single tab to see the measurements in numeric and graphical form. Set

the graph scales manually by making a note of the current Mean value and

pressing Set Scales. This opens the graph scales window. Ensure that autoscaling

is turned off (press Autoscale to toggle autoscaling on/off, the status of

autoscaling is shown by the adjacent indicator). Use the ellipses buttons to set the

y-axis limits to be 0.005°C above and below the current mean value. Use the

radio and up/down buttons to set the x-axis to 5 minutes:

Press OK to return to the main window. The measurement system will now

accumulate data and after 5 minutes the graph will begin to scroll to show the

last 5 minutes of data:

2.2 Measuring Temperature with a Thermocouple

From startup, press Resume to restart your microK:

This tutorial describes the use of an uncalibrated type-N thermocouple. The

microK can be used with calibrated thermocouples, in which case you will need

to enter information about the thermometer into the microK’s database and (see

section 3.7.1) and select this thermometer entry from the Thermometer box in the

Settings tab (see later in this tutorial). When the main window opens, press the

Settings tab:

In the Settings tab disable channels 2 and 3 (this will speed up measurements on

channel 1, which we will be using) by using the up/down buttons by the Channel

box to select these channels and pressing Disable. Use the up/down buttons to

return to channel 1. Use the up/down buttons by each box to select the required

settings:

The reference junction is assumed to be an ice point in this tutorial. It can be set

to the water triple-point or to use a temperature measured by one of the other

channels (see sections 3.6 and 4.6) if using reference junction compensation.

Connect the N-type thermocouple to channel 1 (see section 4.5 for details on how

to connect thermocouples). Press the Single tab to see the measurements in

numeric and graphical form. Set the graph scales manually by making a note of

the current Mean value and pressing Set Scales. This opens the graph scales

window. Ensure that autoscaling is turned off (press Autoscale to toggle

autoscaling on/off, the status of autoscaling is shown by the adjacent indicator).

Use the ellipses buttons to set the y-axis limits to be 0.01°C above and below the

current mean value. Use the radio and up/down buttons to set the x-axis to 5

minutes:

Press OK to return to the main window. The measurement system will now

accumulate data and after 5 minutes the graph will begin to scroll to show the

last 5 minutes of data:

3 Driving Your microK

3.1 Introduction

The operator interface for the microK is provided through the touch screen and

colour display. The software is written in Microsoft’s new C# language and runs

under the Windows CE™ operating system. This provides a familiar and easy to

use interface.

The buttons in the microK software have been sized and positioned to allow you

to operate the instrument with your finger. If numeric or alphanumeric data needs

to be entered, a ‘soft’ keyboard window appears. If you are unfamiliar with touch

screen devices such as PDAs, you may initially feel that the touch screen

interface is slow compared with using a mouse and keyboard, but with a little

practice you should quickly become comfortable with the technology and

appreciate its benefits. However, if you prefer to use a USB mouse or keyboard,

you can simply plug these into the USB connector on the front panel. They will

immediately become active provided they use the standard class drivers built into

the Windows CE™ operating system used in the microK. To use more than one

USB device, simply plug a USB hub into the front panel connector.

Calibration data entered into the microK’s database is password protected and

includes recalibration dates (the microK will alert you if you try to use a

thermometer or reference resistor after its recalibration date). This feature

ensures the integrity of your measurements and helps you to comply with the

requirements of accreditation bodies.

3.2 The Startup Window

When power is applied to the microK, it goes through a Windows CE™ boot

sequence that loads the operating system and then starts the microK application.

The Startup Window then appears showing the microK’s model and serial

number together with the version numbers for the measurement system firmware

and microK software used. The window also lists the details of any

“microsKanner” multiplexers connected to the microK (the microsKanner

manual describes how to use “microsKanner” multiplexers with your microK

bridge). The Startup Window contains the Resume button:

Resume: Pressing the Resume button places the microK in the state it was in

prior to its last power down. Before pressing Resume, make sure that any

thermometers attached will not be damaged by the sense currents that will be

applied (the last values used). If there is a problem, disconnect your sensors

before proceeding and then reconnect them after changing the sense current to

the required values.

3.3 The Main Window

Having pressed Resume in the Startup Window, the user is presented with the

Main Window.

displays all three ch

annels in numeric form

allows you to configure the channels to perform the

All functions to control the microK are available in this Window, which is

divided into four tabs:

Single

displays a single channel in numeric and graphical form

Multi

Settings

required measurement

Instrument

allows you to enter information on the thermometers and reference resistors used with the instrument into its database. It also allows you to save/load measurement data and instrument configurations in the database and to change instrument settings such as the GPIB address, time/date and security passwords

The Main Window opens with the Single tab selected.

3.4 The Single Tab

Select this tab to see a single channel in both numeric and graphical form:

Channel box: Use the up/down buttons by the Channel box to select the channel

you wish to view. Alternatively press the ellipses button to open a numeric entry

window and select the channel directly. The ellipses button is particularly useful

when the microK is used with microsKanner multiplexers, which can provide up

to 90 expansion channels. You can only view channels that are enabled, so if a

channel is disabled in the Settings tab it will not appear in the sequence and will

not be measured. This means that the up/down buttons have no effect if only one

channel is enabled.

The numeric display shows the last reading together with the mean and standard

deviation of the most recent of readings (the number of readings in the statistics

is set in the Settings tab).

Clear Graph: Press the Clear Graph button to clear the graph and re-start the

autoscaling feature. This can be used to eliminate the effect of a large transient

result (perhaps caused when changing connections to the thermometer) on the

autoscaling function.

Clear button: Press the Clear button to clear (reset) the statistics.

Set Scales button: Use the Set Scales button to open a new window and set the x

and y axes for the graphical output:

In this window, use the up/down buttons by the Channel box to select the

channel whose scales you wish to change (the window opens with the currently

displayed channel selected). Use the radio buttons to select either Seconds or

Minutes as the units. Use the up/down buttons by the Scale / Seconds box to

change the x-axis (time) scale (the same x axis scale is used for all channels). Or,

press the ellipses button to open a Numeric Keypad window and enter the

required scale directly. Any value between 1 second and 1000 minutes

(inclusive) may be used.

Use the ellipses by the Minimum and Maximum boxes to open a Numeric Keypad

window and set the y-axis scale. Alternatively, press the Autoscale button to

scale the y-axis so that it will show all the readings. The indicator by the

Autoscale button shows whether autoscaling is active.

The numeric and graphical outputs are updated as new readings are made. The

time between readings depends on the settings for that channel and any other

channels that are also enabled. This can vary between 2 seconds and 5 minutes.

The measurement sample time for a PRT or thermistor is <2s and for a

thermocouple it is <1s. The reading rate for three PRTs with one sample per

reading will therefore be <6s.

Start Save button: Press the Start Save button to record all the measurements

being made. You will then be offered the choice (buttons) of storing the data to

the Internal “DiskOnChip” (solid state drive) memory or an External USB flash

drive. Data stored to the internal memory can subsequently be transferred to an

external USB flash drive using the Backup Data button in the Instrument tab (see

section 3.7.9). The internal memory used has a capacity of at least 32Mbytes; this

will accommodate approximately 1,300,000 PRT readings or about 30 days of

continuous logging at the fastest rate. Select the destination for the data to open

an Alpha-Numeric Keyboard window and enter a filename. An automatically

incrementing default name will appear in the entry box, press OK to accept this

or use the backspace and alpha-numeric keys to enter your preferred filename. If

you try to use a filename that has already been used, you will have to enter the

password to proceed (see section 3.11 for details on password protection). The

Shift key toggles the alpha keys between upper and lower case. The indicator by

the Start Save button in the Single tab shows whether readings are being recorded

to a file. The measurements are written to the file in comma delimited ASCII text

form allowing easy importation into Microsoft Excel™ or other applications.

3.5 The Multi Tab

Select this tab to see all three channels in numeric form only. The numeric

display shows the last reading together with the mean and standard deviation for

the most recent readings (the number of readings in the statistics is set in the

Settings tab) for each of the channels that are enabled.

Clear buttons: Press the Clear button to clear (reset) the statistics for each

channel

The displayed values are updated as new readings are taken. The time between

readings depends on the settings for that channel and any other channels that are

also enabled. This can vary between 2 seconds and 5 minutes. The measurement

time for a PRT or thermistor is <2s and for a thermocouple it is <1s. The reading

rate for three PRTs with one sample per reading will therefore be <6s.

Start Save: Press the Start Save button to record all the measurements being

made. You will then be offered the choice (buttons) of storing the data to the

Internal “DiskOnChip” (solid state drive) memory or an External USB Flash

Drive. Data stored to the internal memory can subsequently be transferred to an

external USB Flash Drive using the Backup Data button on the Instrument tab

(see section 3.7.9). The internal memory used has a capacity to at least

32Mbytes; this will accommodate approximately 1,300,000 PRT readings or

about 30 days of continuous logging at the fastest rate. Select the destination for

the data to open an Alpha-Numeric Keyboard window and enter a filename. An

automatically incrementing default name will appear in the entry box, press OK

to accept this or use the backspace and alpha-numeric keys to enter your

preferred filename. If you try to use a filename that has already been used, you

will have to enter the password to proceed (see section 3.11 for details on

password protection). The Shift key toggles the alpha keys between upper and

lower case. The indicator by the Start Save button in the Multi tab shows whether

readings are being recorded to a file. The measurements are written to the file in

comma delimited ASCII text form allowing easy importation into Microsoft

Excel™ or other applications.

3.6 The Settings Tab

Select this tab to configure each channel for the required measurements.

Channel box: Use the up/down buttons to select the channel you wish to

configure. Alternatively press the ellipses button to open a numeric entry window

and select the channel directly. The ellipses button is particularly useful when the

microK is used with microsKanner multiplexers, which can provide up to 90

expansion channels.

Enable/Disable button: Use this button to enable or disable a channel. Disable

unused channels to skip measurements on that channel and reduce the cycle time

through the channels. The nearby indicator shows whether the currently selected

channel is enabled.

Thermometer box: Use the up/down buttons to select the required thermometer.

Initially this box will contain only default PRT, Thermocouple or Thermistor.

You can use these entries for uncalibrated thermometer sensors. If you add

thermometers to the microK’s Thermometer Database (see section 3.7.1), these

will also appear in the list within this box. The ellipses button opens a list of all

available thermometers and is useful if you have a large number of entries in the

database.

Conversion box: If the selected thermometer is one of the default types, you can

use the up-down buttons to select a standard polynomial function for converting

the thermometer’s base measurement to temperature. If the selected thermometer

is one that your have created in the Thermometer Database this box will be fixed

and will be the conversion type defined for that thermometer.

Range box: Use the up/down buttons to select the required range. The microK

has three ranges for each thermometer type. Use the 0.125V range for all

thermocouples as this provides the most suitable input voltage range. The

resistance ranges offered depend on the sense current (use the ellipses button by

the Current box in this tab to change the current). Choose a resistance range that

is greater than or equal to both the highest thermometer resistance and reference

resistor value you intend to use.

Reference Channel box (PRTs and thermistors only): Use the up/down

buttons to select the reference resistor used in the resistance measurement; either

one of the internal reference resistors or the channel to which an external

resistance standard is connected. Alternatively press the ellipses button to open

the Reference Channel window and select the channel directly. The External

button in this window allows you to select one of the microK’s three external

channels or any expansion channel provided by a microsKanner.

Reference Resistor box (PRTs and thermistors only): If an internal reference

resistor was selected in the Reference Channel box, this box will show the

calibrated value of that resistor. If one of the input channels was selected in the

Reference Channel box, this box will contain a list of the reference resistors in

the microK’s database (entered using the Edit Resistors button in the Instrument

tab – see section 3.7.2) and “Uncalibrated”. Select the required resistor using the

up/down buttons. Select “Uncalibrated” if you only want to make a resistance

ratio measurement between two channels. The ellipses button opens a list of all

available reference resistors and is useful if you have a large number of entries in

the database.

Reference Junction box (thermocouples only): This contains 0°C, 0.01°C and

a list of any input channels that have been configured to measure temperature.

Choose 0°C or 0.01°C if you are using an external reference junction in an ice-

point bath or water triple point respectively. Choose one of the measurement

channels if you want to measure the temperature of the reference junction with a

thermometer sensor on that channel. The software will not allow you to use a

thermocouple channel as the reference junction sensor (to avoid circular

dependencies). You must specify a thermometer sensor for the reference junction

channel that includes temperature conversion otherwise it will not appear in the

Reference Junction box.

Units box: Use the up/down buttons to select the required units. The base units

(resistance ratio “Rt/Rs” for PRTs or thermistors and “Volts” for thermocouples)

are always available. “Ohms” will also be available (for PRTs and thermistors) if

the value of the reference resistor is available (Reference Resistor not set to

“Uncalibrated”). If the thermometer sensor chosen has a temperature conversion

specified, then temperature units °C, °F and K are also available.

Current box (PRTs and thermistors only): Press the ellipses button to change

the sense current. Use the buttons in the window that then opens to select the

required sense current:

The standard PRT sense currents are available directly through the buttons

provided. Press the Custom button to specify a different value (range 0 to 10mA),

this will then open a Numeric Keypad window.

Buttons for ÷√2 and ×√2 are included to make extrapolation to zero power easier

since changing the current in a resistor by a factor of √2 changes the power

dissipated by a factor of 2. A PRT’s calibration may be defined at a specified

current. Alternatively, it may be specified at zero power. In this case, you need to

determine what the resistance of the PRT would be at zero power. This is most

easily done by measuring its resistance at the normal sense current and then increasing the current by a factor of √2 and repeating the measurement. If you

subtract the change in resistance from the first resistance value (at nominal

current) this gives you the resistance of the PRT at zero power. Alternatively, the

second measurement can be made at a current that has been reduced by a factor of √2. In this case the change in resistance should be subtracted from the second

resistance value (current scaled by √2) to determine the zero power resistance.

The accuracy of the current source is 0.4%, so the uncertainty associated with

this extrapolation back to zero power is only 0.8% of the measured resistance

change, which should be very small. Other factors such as the fact that the PRT

is not a constant resistance and so the power dissipated has changed between the

two measurements are insignificant.

Samples per Reading box: Use the up/down buttons to select the number of

samples you want to average together to form a single reading. Alternatively,

press the ellipses button to open a Numeric Keypad window and enter the

required number directly. The number of samples may be between 1 and 100

inclusive.

Increasing the number of samples will slow down the rate at which readings are

made, but will also reduce the uncertainty associated with these readings (as

shown by the standard deviations reported in the “Single” and “Multi” tabs). This

uncertainty reduction is proportional to the square-root of the number of samples

(for example: selecting 9 samples per reading will reduce the uncertainty

associated with each reading by a factor of 3).

Readings in Rolling Statistics box: Use the up-down buttons to select the

number of samples in the rolling statistics. Alternatively press the ellipses button

to open a Numeric Keypad window and enter the value directly. Values between

1 and 1000 (inclusive) may be used.

3.7 The Instrument Tab

Select this tab to enter information into the microK’s database (for thermometers

and reference resistors), adjust instrument settings (GPIB address, time, date and

passwords), backup/load instrument configurations or update the software:

3.7.1 Edit Thermometers

Press Edit Thermometers to create, edit or delete a thermometer in the database.

You will be prompted to enter the password in order to proceed.

Thermometer box: Use the up/down buttons to select the thermometer you wish

to edit or delete. Alternatively press the New key to create a new thermometer

entry. The default thermometer types are included in the list but cannot be edited

or deleted.

Thermometer Name box: This box contains the name of the selected

thermometer. If you are creating a new thermometer entry, the ellipses button by

the box becomes active. Press this button to open an Alpha-Numeric Keyboard

window and enter a name. The Shift key toggles the alpha keys between upper

and lower case.

Manufacturer’s Name box: This box contains the manufacturer of the selected

thermometer. If you are creating a new thermometer entry, the ellipses button by

the box becomes active. Press this button to open an Alpha-Numeric Keyboard

window and enter a name. The Shift key toggles the alpha keys between upper

and lower case.

Serial Number box: This box contains the serial number of the selected

thermometer. If you are creating a new thermometer entry, the ellipses button by

the box becomes active. Press this button to open an Alpha-Numeric Keyboard

window and enter a serial number. The Shift key toggles the alpha keys between

upper and lower case.

Calibration Due box: This box contains the date when calibration is due for the

selected thermometer. If you are creating a new thermometer entry, the ellipses

button by the box becomes active. Press this button to open a Date Entry window

and enter a date. The ellipses buttons by the Day, Month and Year boxes in the

Date Entry window open a Numeric Keypad window. Dates are checked for

validity (including leap years) for dates up to 31st December 2099.

Thermometer Type box: This box contains the type of thermometer (PRT,

Thermocouple or Thermistor). If you are creating a new thermometer entry, use

the up/down buttons to select the thermometer type.

Min Temperature box: This box contains the minimum operating temperature

for the selected thermometer. If you are creating a new thermometer entry, the

ellipses button by the box becomes active. Press this button to open a Numeric

Keypad window and enter the minimum operating temperature for the

thermometer.

Max Temperature box: This box contains the maximum operating temperature

for the selected thermometer. If you are creating a new thermometer entry, the

ellipses button by the box becomes active. Press this button to open a Numeric

Keypad window and enter the maximum operating temperature for the

thermometer.

Conversion box: This box contains the conversion to temperature units used for

the selected thermometer. If you are creating a new thermometer entry, use the

up/down buttons to select the required conversion.

Coefficients button: This button opens a window that allows you to enter the

coefficients required for the temperature conversion. In the case of ITS-90, or

thermocouples, these are the coefficients for the deviation function (the base

conversion coefficients are fixed):

New button: Press this button to make a new thermometer entry into the

microK’s database (ellipses and up/down buttons by the boxes then become

active).

Delete button: Press this button to delete the selected thermometer (or the

current entry for a new thermometer) from the database.

OK button: Press this button to confirm the changes and close the Window.

3.7.2 Edit Resistors

Press the Edit Resistors button to create, edit or delete a reference resistor in the

database. You will be prompted to enter the password in order to proceed.

Resistor box: Use the up/down buttons to select the reference resistor you wish

to edit or delete. Alternatively press the New key to create a new reference

resistor entry. The internal reference resistors are included in the list but cannot

be edited or deleted.

Resistor Name box: This box contains the name of the selected reference

resistor. If you are creating a new reference resistor entry, the ellipses button by

the box becomes active. Press this button to open an Alpha-Numeric Keyboard

window and enter a name. The Shift key toggles the alpha keys between upper

and lower case.

Manufacturer’s Name box: This box contains the manufacturer of the selected

reference resistor. If you are creating a new reference resistor entry, the ellipses

button by the box becomes active. Press this button to open an Alpha-Numeric

Keyboard window and enter a name. The Shift key toggles the alpha keys

between upper and lower case.

Serial Number box: This box contains the serial number of the selected

reference resistor. If you are creating a new reference resistor entry, the ellipses

button by the box becomes active. Press this button to open an Alpha-Numeric

Keyboard window and enter a serial number. The Shift key toggles the alpha

keys between upper and lower case.

Calibration Due box: This box contains the date when calibration is due for the

selected reference resistor. If you are creating a new reference resistor entry, the

ellipses button by the box becomes active. Press this button to open a Date Entry

window and enter a date. The ellipses buttons by the Day, Month and Year boxes

in the Date Entry window open a Numeric Keypad window. Dates are checked

for validity (including leap years) for dates up to 31st December 2099.

Value box: This box contains the calibrated value for the selected reference

resistor. If you are creating a new reference resistor entry, press the ellipses

button to open a Numeric Keypad window and enter the calibrated resistance

value (in ohms).

New button: Press this button to make a new thermometer entry into the

microK’s database (ellipses and up/down buttons by the boxes then become

active).

Delete button: Press this button to delete the selected reference resistor (or the

current entry for a new reference resistor) from the database.

OK button: Press this button to confirm the changes and close the Window.

3.7.3 Calibration

Press the Calibration button to open a Date Entry window and set a recalibration

date for your microK. The microK will warn you if you attempt to use it past this

recalibration date (you can disregard the warning and continue to use it, but the

warning will continue to re-appear every hour until the out-of-calibration issue is

resolved).

3.7.4 Restart Software

Press the Restart Software button to restart the microK software. This is useful if

you have added or removed microsKanners and want to re-invoke the automatic

discovery process without cycling the power.

3.7.5 Update Software

Press the Update Software button to update the software or firmware in your

microK. The software runs on a 32-bit processor and provides the operator

interface. The firmware runs on an 8-bit processor and controls the low-level

hardware in the microK.

The new software (microk.exe) or firmware (microK version x_xx.hex) should

be located in the root directory of a USB flash drive connected to the front panel

USB connector (some USB flash drives can take a long time to enumerate in

Windows CE™ and become visible to the software. You should therefore wait

15 seconds between plugging in the drive and pressing the button). You will be

warned that this operation will restart the software, press Yes if you wish to

continue. If the software finds a more recent software or firmware on the flash

drive you will be advised of the version levels and offered the opportunity to

update to the later version, you will also be prompted to enter the password

before proceeding. If the flash drive does not contain a more recent version, the

software will simply restart.

If you are updating the firmware, you will need to cycle the power to the microK

(instruction provided on-screen) before the update process starts (it will take

about 5 minutes). The update software will only update either the software or

firmware at each attempt, so if you are updating both you will need to press

Update Software twice.

The software automatically checks any USB flash drive connected to the front

panel at start-up. If a more recent software version is found, you will be offered

the opportunity to upgrade. Some flash drives enumerate too slowly and so are

not detected during the start-up routine; in this case you should use the manual

update procedure described above.

3.7.6 Change Password

Press the Change Password button to change the security password. (see section

3.11 for details of password protected settings). A window will then open to

allow you to change the password.

You will need to enter the old password and the new one (twice to ensure that it

has been correctly entered). Press the ellipses buttons by each of the password

boxes to open an Alpha-Numeric Keyboard window and enter the relevant

password. Your microK is shipped with the password set to “1234”. This should

be changed, for security reasons, before using your instrument in earnest.

3.7.7 Port Settings

Press Port Settings to view and change the microK’s GPIB address:

Press the ellipses button to open a numeric entry window and change the GPIB

address (valid range 1 to 30 inclusive). The Baud Rate box reports the baud rate

for the RS232 port, but this cannot be changed.

3.7.8 Set Date and Time

Press Set Date and Time to change the date and/or time. This opens a window to

allow you to enter the current date and time and to select the date format

(dd/mm/yyyy or mm/dd/yyyy):

Press the ellipses buttons by each box to open a Numeric keypad window and

enter the required value.

Press OK to save the changes and close the window. Press Cancel to close the

window without making any changes.

3.7.9 Backup Data

Press Backup Data to transfer data that has been saved to the internal memory

(see section 3.4 or 3.5) to an external USB Flash Drive. You need to plug a USB

Flash Drive into the front of the microK in order to use this facility. With some

Flash Drives, it can take up to 15 seconds for these to enumerate and therefore be

recognised by the Windows CE operating system, you therefore need to wait for

15s after plugging in the USB Flash Drive before attempting to transfer the data

(otherwise a “No external drive present” warning will appear).

If a file with the same name is already present on the USB flash drive, you will

be asked whether you wish to over-write it. To proceed, you will need to enter

the password.

Files are transferred to the USB flash drive in directory

\\microKData\serialnumber\data, where “serialnumber” is the serial number of

the microK used to make the measurements. This means that you can have

duplicate filenames for measurements, provided they are made with different

instruments.

3.7.10 Clear Data Files

Press Clear Data Files to delete the data files from the internal memory, this

frees up space for new files to be recorded. You will be prompted to enter the

password before proceeding.

Unless you are sure that you do not need any of the files in the internal memory,

you should transfer all files from the internal memory to a USB flash drive (see

section 3.7.9) before using this feature.

3.7.11 Backup Configuration

Press Backup Configuration to save the current configuration (settings) of the

microK. You will be prompted to enter the password before proceeding. You will

then be offered the choice (buttons) of storing the configuration to the Internal

“DiskOnChip” (solid state drive) memory or an External USB flash drive. Press

the required button to open an Alpha-Numeric Keyboard window and enter a

name for the configuration.

Configurations stored to a USB flash drive are located in directory

\\microKData\serialnumber\backups, where “serialnumber” is the serial number

if the microK. This means that you can have duplicate configuration names

(filenames) for measurements provided they apply to different instruments. If

you want to transfer a configuration from one microK to another, you will need

to move the configuration file manually on the USB flash drive between the sub-

directories for the two microKs.

3.7.12 Load Configuration

Press Load Configuration to load a configuration (settings) for the microK. You

will be prompted to enter the password before proceeding. You will then be

offered the choice (buttons) of loading the configuration from the Internal

“DiskOnChip” (solid state drive) memory or an External USB flash drive. Press

the required button and then use the up/down buttons to select the required

configuration. Press OK to load the configuration, or press Cancel to close the

Window without loading the configuration.

3.8 Using the Thermometer Database

The microK contains a database that allows you to enter, review and edit

information about the thermometers you use. You can then select a thermometer

from this database and all the parameters associated with it will be loaded and

used by the measurement system. This means that you do not need to enter

information such as the calibration coefficients each time you use the

thermometer and therefore avoids the associated risk of data entry errors.

The database also allows you to enter calibration due dates to ensure that you do

not unwittingly use devices beyond their recalibration date. The microK will

warn you if you attempt to use a thermometer past its recalibration date (you can

disregard the warning and continue to use the thermometer, but the warning will

continue to re-appear every hour until the out-of-calibration issue is resolved).

Enter data on the thermometers you use as reference standards or measurement

devices into the microK’s database (see section 3.7.1). You can then use one of

these thermometers by selecting it in the Thermometer box in the Settings tab

(see section 3.6).

The database allows you to enter information about the thermometer:

 Thermometer Name (the name you use to refer to the thermometer)  Manufacturer’s name  Serial Number  Calibration Due date  Thermometer Type  Minimum Temperature (operating)  Maximum Temperature (operating)  Conversion (algorithm for converting base reading to temperature)

Information in the database is password protected to help you comply with the

requirements of accreditation bodies.

3.9 Using the Reference Resistors Database

The microK contains a database that allows you to enter, review and edit

information about the reference resistors you use. You can then select a reference

resistor from this database and all the parameters associated with it will be

loaded and used by the measurement system. This means that you do not need to

enter its value each time you use it and therefore avoids the associated risk of

data entry errors.

The database also allows you to enter calibration due dates to ensure that you do

not unwittingly use devices beyond their calibration interval. The microK will

warn you if you attempt to use a reference resistor past its recalibration date (you

can disregard the warning and continue to use it, but the warning will continue to

re-appear every hour until the out-of-calibration issue is resolved).

Enter data on the reference resistors you use with your resistance thermometers

into the microK’s database (see section 3.7.2). You can then use one of these

reference resistors using the Reference Resistor box in the Settings tab (see

section 3.6).

The database allows you to enter information about the reference resistor:

 Resistor Name (the name you use to refer to the resistor)  Manufacturer’s name  Serial Number  Calibration Due date  Value (calibrated value in ohms)

Information in the database is password protected to help you comply with the

requirements of accreditation bodies.

3.10 Saving Instrument Configurations

You can save the current configuration (settings) for the microK using the

Backup Configuration button in the Instrument tab (see section 3.7.11). This is

useful if you use the microK in a number of different ways (for example at

different times you may use it to perform fixed-point calibrations on single

SPRTs and comparison calibrations of a thermocouple against two SPRTs). You

can then reload the required configuration (see section 3.7.12) rather than having

to enter all the setting for that particular measurement configuration individually.

3.11 Password Protection of Key Settings

All settings and parameters that affect measurements are password protected.

This helps you to establish working procedures that meet the requirements of

accreditation bodies and should alleviate some of the concerns that accreditation

bodies have about the integrity of measurements.

You need to enter the password to perform the following tasks:

 create/edit/delete a thermometer database entry  create/edit/delete a reference resistors database entry  backup internal data to a USB flash drive  overwrite a data file on the USB flash drive  delete internal data files  backup a configuration  load a configuration  change the password  upgrade the software

4 Connecting Thermometer Sensors

4.1 The “Cable-Pod” Connectors

The Eichmann “Cable-Pod”™ connectors used on the microK have gold-plated

tellurium-copper contacts. These generate exceptionally low thermal EMFs when

connected to the copper terminations used on standards grade thermocouples.

The connectors accept 4mm plugs, bare wires or spade terminations.

Additionally, they are spaced on 19mm (¾”) pitch so that they can be used with

standard 4mm-to-BNC adaptors (not supplied) for connecting to BNC terminated

SPRTs. The mechanism is designed so that the clamping surface does not rotate

as it clamps the wire in order to avoid damaging it.

The “Cable-Pod”™ mechanism is made from a high strength polymer but

nonetheless may be subject to mechanical damage if the connectors are over

tightened. Please tighten the terminals to a light “finger-tight” level in order to

ensure that they are not subject to undue wear or premature failure. This is all

that is required electrically – do not try to use the connector to provide strain

relief or tension a cable.

4.2 Connecting PRTs (4-wire)

The microK’s resistance measurement system is optimised for high accuracy, 4-

wire resistance measurement. The PRT should be connected to the chosen input

channel in accordance with the schematic shown on the microK’s front panel, as

follows:

V I

SPRT

The top terminal should be connected to the screen of the SPRT’s lead to

minimise electrical noise picked up by the wires.

4.3 Connecting PRTs (3-wire)

The microK can be connected to 3-wire PRTs, although it will not automatically

compensate for cable resistance. The two red terminals should be connected

together and then connected to the ‘single’ end of the 3-wire PRT as follows:

V I

PRT

The connection to the ‘single’ end of the 3-wire PRT should be short (have a low

resistance) in order to minimise the effect of lead resistance on the measurement.

The top terminal should be connected to the screen of the PRT’s lead to minimise

electrical noise picked up by the wires.

4.4 Connecting PRTs (2-wire)

The microK can be connected to 2-wire PRTs. The two red and two black

measurement terminals should be connected together and then connected to the

PRT as follows:

V I

PRT

The connections to the PRT should be short (low resistance) in order to minimise

the effect of lead resistance on the measurement. Alternatively, the connections

can use remote sensing (using the 4-wire measurement capability of the microK)

to eliminate the effect of lead resistance completely. In this arrangement, the

current and voltage sense connections are kept separate and are only joined close

to the PRT:

V I

PRT

The top terminal should be connected to the screen of the PRT’s lead to minimise

electrical noise picked up by the wires.

4.5 Connecting Thermocouples (external Ice Point or

WTP)

The microK’s measurement system uses active guarding. As a result, the voltage

measurement system is floating until it is connected to the sense current

terminals. In order to measure the voltage on a thermocouple, the two current

terminals should be connected to each other and to the red voltage sense

terminal:

Thermocouple

V I

Measurement

The most accurate thermocouple measurements are made with the reference

Reference

JunctionJunction

junction immersed in an ice-point bath (or water-triple-point). The microK

supports this arrangement by allowing you to specify the temperature of the

reference junction as 0°C or 0.01°C (see section 3.6).

4.6 Connecting Thermocouples (using RJ compensation)

It is possible to measure the temperature of the reference junction and

compensate for the associated EMF at this junction. The reference junction can

be measured using a PRT or thermistor connected to another measurement

channel:

Thermocouple

Measurement

V I

Reference

JunctionJunction

PRT

V I

The microK supports this arrangement by allowing you to use a temperature

measured by another input channel as the reference junction temperature. This

technique is less accurate than using an ice-point (or water-triple-point) due to

the additional uncertainties associated with the PRT used to monitor the

reference junction and any temperature gradients that result in a difference

between the temperature of the PRT and the reference junction.

4.7 Connecting Thermistors

The microK can be connected to thermistors using the same arrangement as for

2-wire PRTs (see section 4.4):

V I

THERMISTOR

Because the resistance of thermistors used for temperature measurement is much

higher than for PRTs, lead resistance is not normally a problem.

Use an external reference resistor with thermistors since the resistance of the

internal standards is too low. Thermistors have much higher temperature

coefficients than PRT, so the tolerances on the reference resistor are

correspondingly less demanding, making them relatively inexpensive.

The top terminal should be connected to the screen of the thermistor’s lead to

minimise electrical noise picked up by the wires. The high resistance of

thermistors makes them more prone to picking up electrical noise, it is therefore

even more important to use a screened cable and connect this to the screen

terminal on the microK than when using PRTs.

5 Good Practice Guidelines

5.1 Looking After Your microK

Your microK is a precision electronic instrument intended for indoor use in a

laboratory or office environment. Nonetheless, it has been designed to be as

robust as practical and will provide many years of service, provided it is properly

maintained.

We recommend that you return your microK to Isothermal Technology or one of

our approved service centres on an annual basis for calibration. Isothermal

Technology has developed a calibration kit for the microK. Contact Isothermal

Technology or one of our appointed distributors if you wish to purchase a kit to

calibrate the microK yourself. The microK should require little maintenance

between calibrations other than routine cleaning.

Under no circumstances should you use sharp or unsuitable objects (such as ball-

point pens) on the touch screen as this will lead to premature failure. It is also a

good idea to ensure that you have clean hands when using the touch screen. You

should ensure that you do not have contaminants such as adhesives or solvents

on you fingers when touching the screen as these will be difficult to remove

without damaging the screen.

The touch screen can be cleaned with a damp (not wet) cloth. Use either a

proprietary screen cleaner (suitable for PC flat panel displays) or water and a

little mild liquid soap on a lint-free cloth to wipe the touch screen. Dry the screen

immediately after cleaning with a lint-free cloth. The rest of the microK should

not require cleaning as often as the display, and can be cleaned in the same way

as the screen. Never use abrasive cleaners (such as ‘cream’ cleaners) on your

microK.

5.2 Making a Good Electrical Measurement

Although the microK is intended for use in temperature metrology, its base

measurements are electrical (resistance or voltage). The limited sensitivity of

PRTs and thermocouples means that in order to achieve uncertainties at the mK

level, we need to make electrical measurements that rival those of a good

electrical metrology laboratory. For example, for a 25Ω SPRT a 1mK

temperature uncertainty corresponds to 100µ Ω resistance uncertainty. With a

1mA sense current, this corresponds to a voltage uncertainty of 0.1µV.

The microK has been optimised for electromagnetic compatibility (minimising

emissions and maximising immunity). However, since the microK is capable of

measuring to such low signal levels it is worthwhile adopting good electrical

measurement practices. Here are a few guidelines:

 The most sensitive points are the inputs to the microK (measuring to

better than 0.1µV). Whilst the microK will work satisfactorily with just a

four wire connection to the PRT or reference resistor (using the voltage

sense and current terminals marked “V” and “I” respectively), it is better

to use a screened cable and to connect the screen to the measurement

ground terminal above the input terminals:

Screen (Measurement Ground) Terminal

V I

SPRT or

Reference Resistor

The screen should also be connected to the outer sheath of the SPRT (if it

is metal clad) or the case of the reference resistor. The use of screened

cables is more important when the microK is used with thermistors, which

have a higher resistance than PRTs or thermocouples.

 Keep the cables to the microK input terminals away from other cables

that might be sources of electrical noise (for example electrical supplies

to furnaces).

 The insulation in high temperature furnaces (any that ‘glow’) begins to

conduct at higher temperatures. This can cause high common-mode

voltages on any thermometer in the furnace. Whilst the microK is

designed to reject common-mode DC and AC signals (at both 50 and

60Hz), it is good practice to minimise them. It is common practice to use

a metal equalising block in a furnace when performing comparison

calibrations. This should be connected to the safety earth of the electrical

supply (most furnaces designed for temperature metrology applications

are fitted with a device to ‘earth’ the equalising block). Do not ‘earth’ the

equalising block to the screen/measurement ground terminals on the front

panel of your microK as this is not connected to the safety earth of the

electrical supply.

 Provide a ‘clean’ electrical environment in your temperature laboratory. It

may be useful to filter your electrical supply into the laboratory especially

if other heavy electrical machinery is being used nearby on the same

supply (the microK has very good immunity to electrical noise conducted

along the electrical supply, but other equipment in your laboratory may

be more sensitive). It is worth avoiding using sources of electrical signals

or noise in your laboratory. Examples include furnaces with triac controls

(especially those that ‘chop’ the electrical supply part way through a

cycle – better controllers switch only at the zero-crossing point to ‘chop’

whole cycles only), mobile phones (the microK is not significantly

affected by mobile phones, but other equipment may be more sensitive).

6 The microK Technology

The microK uses a number of new technologies and measurement techniques to

achieve performance that has not previously been available with potentiometric

measurement systems.

6.1 The ADC

The ADC (Analogue-to-Digital Converter) in a precision instrument is the

‘measurement engine’. Its performance is the starting point for achieving low

measurement uncertainty. The microK uses a completely new type of ADC,

which was designed specifically for this product. It is based on the well

established Σ-∆ (sigma-delta) technique but uses multi-bit feedback to achieve

performance that is not achievable with conventional Σ-∆ ADCs.

In a conventional Σ-∆ ADC, the analog input signal is subtracted from the output

of a 1-bit DAC before being filtered by a series of cascaded integrators. The

signal then passes to a 1-bit ADC that drives the DAC and forms a feedback loop

Integrators

INPUT Digital

1-Bit DAC

1-Bit ADC

Filter

OUTPUT

VALUE

Conventional Σ-∆ ADC

The extremely high, low-frequency loop-gain of the cascaded integrators ensures

that the input signal is balanced against the output of the DAC so that the average

value of the 1-bit data stream from the DAC equals the input signal. A low-pass

digital filter is then used to extract the converted value from the 1-bit data

stream.

120 kHz

Digital

Filter

Decimator

output

32 bits

Another way of viewing the operation of a Σ-∆ ADC is to consider what is

happening in the frequency domain. The over-sampling used in Σ-∆ converters

means that the quantisation noise caused by the 1-bit ADC is spread over a wide

bandwidth, whereas the signal we are looking for is unaffected by this over-

sampling. The digital filter selects the narrow bandwidth of the required signal.

The amount of quantisation noise in this bandwidth is relatively small because

the over-sampling spreads the noise power over such a large bandwidth.

The quantisation noise on the converted signal can be reduced by increasing the

sampling rate, but it becomes increasingly difficult to maintain performance as

the clock rate of the system increases. Another way to reduce the noise would be

to use a multi-bit ADC and DAC in the feedback loop. This would not normally

be feasible since the DAC would carry the full accuracy burden of the

measurement system. However, by using a PWM (Pulse-Width Modulation)

DAC, in which the output is a signal of fixed frequency and amplitude but

variable pulse width, we turn the problem of producing accurate voltage or

current levels into one of accurate timing. Whereas achieving sub-ppm voltage

accuracy with a DAC would not be feasible in this sort of product, it is possible

to achieve the corresponding timing accuracies.

Low

Accuracy

5 bit ADC

CLK

LOGIC

“5-bit”

output

data

stream

value

input

buffer

4 integrators

Precise

5 bit

DAC

REF.

Multi-Bit Σ-∆ ADC

The timing demands of the PWM DAC are, however, far from trivial. The digital

filter has to work at the Σ-∆ ADCs clock rate. In the microK, this digital part of

the Σ-∆ ADC is implemented in a fast FPGA, which provides both the digital

filter that decimates the DAC output (to extract the converted value) and controls

the feedback DAC. The full-scale pulse-width on the PWM DAC is only 5µs, so

the 0.2ppm linearity achieved with the Σ-∆ ADC corresponds to a timing

accuracy of 1ps, or about the time it takes for the electrical signals in the control

system to travel 0.3mm.

It might appear that the reduction in quantisation noise from using multi-bit

feedback in a Σ-∆ ADC would be directly proportional to the ADC/DAC

resolution. However, the reduced differential gain inherent in the higher

resolution DAC greatly improves loop stability too. This allows the use of more

orders of integration and higher loop gain giving a disproportionate improvement

in quantisation noise. With the 5-bit system used in the microK, the quantisation

noise is reduced by a factor of 600 so that the performance of the microK is not

limited by the Σ-∆ ADC technique but by the electronic devices used in the ADC

and the rest of the measurement system.

Another benefit of the new ADC is its speed. The implementation used in the

microK provides conversions to full accuracy in 100ms. This, together with the

use of solid-state switching, allows for a very fast reversal rate, which in turn

helps to eliminate the effect of any thermal EMFs and reduce the noise (since the

system can operate above the corner frequency of the amplifiers 1/f noise).

6.2 Substitution Topology

In conventional potentiometric instruments, a common DC current is passed

through a thermometer (RX) and reference resistor (RS). A voltmeter is switched

between reading the voltage across RX and RS and the ratio of the two readings

(n) is calculated:

ADC

Amplifier

Conventional Potentiometric Resistance Measurement

A significant source of error with this measurement topology is the common-

mode rejection ratio of the input amplifier. The common-mode signal at the input

to the amplifier changes between the two measurements and will lead to an error

at the input to the ADC.

In order to eliminate this source of error, the microK uses a substitution topology

in which there is a single point of measurement in the system into which the

SPRT and Reference Resistor are switched alternately.

Resistor Reference

SPRT

ADC

Amplifier

Substitution Measurement Topology

This adds complexity and cost to the design, but ensures that there is no change

to the common-mode signal between the measurement of the reference resistor

and the thermometer. This approach would normally, however, increase the

demands on the current source. In the conventional topology, the current is

common to both the reference resistor and the thermometer. In the substitution

topology, the voltage at the output of the current source changes between the

measurement on the SPRT and the Reference Resistor and the current source

must accommodate this change without any significant change to the sense

current.

The current source in the microK has a very high output impedance, such that the

sense current will not change significantly between the measurement of the

reference resistor and the thermometer. In addition, the whole measurement

system is actively guarded so that both the voltage at the output of the current

source and the common-mode voltage across the device being measured do not

change.

Guard Amplifier

Resistor Reference

SPRT

ADC

Amplifier

Guarded Measurement System

The Guard Amplifier senses the potential at the ‘top’ of the measurement system

and drives the opposite end in order to maintain it at ground potential. In this

way, both the current source and Amplifier see no significant change in

voltage/common-mode signal between the measurements of the Reference

Resistor and the SPRT.

6.3 Minimising Thermal EMFs

Thermal EMFs (EMFs generated as the result of junctions between dissimilar

metals at different temperatures) are a potential source of error when working at

this precision. These can largely be eliminated when measuring resistance

thermometers by reversing the current and averaging the measurements (the

offsets in the two measurements cancel each other out when the readings are

averaged together). However, this technique cannot be used when measuring

temperature with thermocouples, so the thermal EMFs need to be eliminated at

source. For this reason, we used tellurium-copper (gold plated) as the connector

contact material, since this combines good mechanical properties with extremely

low thermal EMFs against the copper terminations of a thermocouple.

In order to eliminate thermal EMFs from the measurement system (already

small), the input connections are reversed immediately behind the input

terminals. Measurements made with and without the reversal are then averaged

together to eliminate the thermal EMFs. The limitation is then the thermal EMFs

generated by the devices used to implement this reversal.

6.4 Solid-State Switching

One of the most common sources of failure in instruments of this complexity is

the contacts in switches, relays, connectors and potentiometers. For this reason,

the microK was designed to have no switches (apart from the on/off switch),

mechanical relays or potentiometers. The switches normally used for the operator

interface have been replaced with a combination of an industrial grade touch-

screen over a full-colour VGA LCD, making the instrument both reliable and

easy to use The internal connectors are limited to three ribbon cables (with gold

plated contacts) for signal interconnections plus a small number of connectors for

the AC power and internal DC supply.

Conventional instruments of this type use mechanical relays for some or all of

the signal routing. The microK uses only solid-state switching. The thermal

EMFs from the metal-silicon junctions in solid-state switching devices are

potentially higher than for mechanical relays under the same temperature

gradient. However, the very small size of the die within the semiconductor

devices means that there would be little opportunity for thermal gradients, giving

them a strong advantage over their mechanical counterparts. In practice the

thermal EMFs from solid-state switching are significantly less than even the best

mechanical relays. As a result, the microK achieves voltage offsets significantly

less that 250nV.

6.5 Inherent Stability

The current reversals used to eliminate thermal EMFs from resistance

measurements together with true 4-wire resistance measurement have the effect

of ensuring an intrinsically stable zero with time and temperature. The voltage at

the amplifier input when measuring a short-circuit will be the same whichever

current direction is used. The process of averaging the measurements therefore

yields zero (with uncertainty determined by the system noise).

In a similar way, the substitution technique means that the measurement system

is also inherently stable at unity ratio since the voltages measured for a reference

resistor and thermometer of the same value will be identical. There is, after all,

no difference between these two measurements apart from the fact that they are

taken at slight different times. The system noise will again determine the

uncertainty of this unity ratio measurement.

6.6 Eliminating Self-Heating Effects

Although the sense currents used with SPRTs are small, they can still generate

self-heating ‘errors’ of several mK. The most accurate SPRTs typically have very

lightly supported elements so the self-heating effect is ironically worst in those

SPRTs designed for the most accurate measurements.

The microK includes individual “keep-warm” current sources for each of the

three input channels. These replace the sense current when a channel is not being

measured and ensure that the power dissipated in an SPRT remains constant.

The most accurate measurements with an SPRT involve measuring its resistance

at two sense currents and then extrapolating back to the zero-power value. The

microK’s user interface provides a simple feature to allow the sense current to be

scaled by a factor of root-two (a factor of 2 in power) to make this technique easy

for the user to implement (see section 3.6).

7 Calibration

The ADC and measurement topology used in the microK are inherently very

stable with both time and temperature. The stability of the microK is primarily

determined by its internal standards (a zener reference for voltage and bulk metal

foil resistors for resistance). We have used the best available components for

these internal standards; a Linear Technology precision zener reference of the

type used for voltage transfer standards in electrical metrology and Vishay

hermetically sealed bulk metal foil resistors. To keep your microK operating

within its performance specification, it should be recalibrated annually. Please

contact Isothermal technology to arrange this calibration.

7.1 Checking Calibration

The calibration can be checked by measuring known standards with the microK.

The calibration should be performed in a temperature controlled environment

between 19°C and 25°C. The microK should be powered up and left to stabilise

in the calibration environment for at least 4 hours before checking or adjusting its

calibration.

7.1.1 Checking the Master Current Source

The microK current source has 3 ranges (0-0.1mA, 0-1mA and 0-10mA). Check

these by connecting a calibrated ammeter (or DMM) across the current terminals

of channel 1 and connecting both the sense inputs to the red current terminal:

V I

Checking the master current source involves connecting a PC to your microK

(using a null-modem RS232 cable) and sending commands to it from

Hyperterminal (part of the standard Windows operating system installation) or

TEST:CURR 10

9.96

to 10.0

4 mA

TEST:CURR

-10 -9.96

to -10.04 mA

another terminal emulator. For further details of how to connect a PC to your

microK see section 8.

Once you have established communication with your microK, type in the

following commands and check that the measured current is within the given

limits:

command current limits

TEST:CURR 0.1 0.0996 to 0.1004 mA

TEST:CURR 1 0.996 to 1.004 mA

TEST:CURR -0.1 -0.09966 to -0.1004 mA

TEST:CURR -1 -0.9966 to -1.004 mA

7.1.2 Resistance Measurements

The current reversal used by the microK to eliminate the effect of thermal EMFs

means that it has an inherently stable zero for resistance measurement. The zero

ohms test does not form part of the calibrations process but is used to confirm

correct operation of the measurement system. It only needs to be checked on one

channel.

7.1.2.1 Zero Ohms Check

Start by applying a four terminal short-circuit to channel 1. This involves

shorting out the voltage sense terminals (marked “V”) and the current terminals

(market “I”) and then making a single connection between these two set of

terminals. The objective is to ensure that none of the sense current passes along

the wire between the voltage sense terminals. This can easily be achieved using a

single piece of un-insulated wire:

V I

4-Terminal Short-Circuit

Configure the microK to measure a Default PRT at 1mA against the internal

100Ω reference on the 125Ω range on channel 1 (other channels disabled). Set

the units to Ohms and use 1 sample per reading and 100 readings in the rolling

statistics (see section 3.6). Select the Single tab and clear the statistic. After the

microK has collected at least 100 readings (shown as Mean of last… in the Single

tab, check that the Mean is less that 0.00001 (10µ Ω i.e. 0.08ppm of the 125Ω

range) and that the standard deviation (S.D.) is less than 0.00005.

7.1.2.2 400 Ω Internal Reference Resistor

Connect a stable external resistance standard with a nominal value of 100Ω to

channel 1. Ideally, this should be a Wilkins resistor with a recent (traceable)

calibration certificate maintained at a constant temperature in an oil bath.

Configure the microK to measure a Default PRT at 1mA against the internal

400Ω reference on the 500Ω range on channel 1 (other channels disabled). Set

the units to Ohms and use 1 sample per reading and 100 readings in the rolling

statistics (see section 3.6). Select the Single tab and clear the statistics. After the

microK has collected at least 100 readings (shown as Mean of last… in the Single

tab, check that the Mean agrees with the calibrated value of the resistance

standard to within 2.5ppm (half of the specification limit) of the calibrated value

and that the standard deviation (S.D.) is less than 0.00008.

7.1.2.3 100 Ω Internal Reference Resistor

Repeat the procedure for checking the 400Ω internal reference (see section

7.1.2.2), but configure the microK to measure a Default PRT at 1mA against the

internal 100Ω reference on the 125Ω range on channel 1.

7.1.2.4 25 Ω Internal Reference Resistor

Repeat the procedure for checking the 400Ω internal reference (see section

7.1.2.2), but configure the microK to measure a Default PRT at 1mA against the

internal 25Ω reference on the 125Ω range on channel 1.

7.1.2.5 10 Ω Internal Reference Resistor

Connect a stable external resistance standard with a nominal value of 10Ω to

channel 1. Ideally, this should be a Wilkins resistor with a recent (traceable)

calibration certificate maintained at a constant temperature in an oil bath. Repeat

the procedure for checking the 400Ω internal reference (see section 7.1.2.2), but

configure the microK to measure a Default PRT at 5mA against the internal 10Ω

reference on the 25Ω range on channel 1.

7.1.2.6 1 Ω Internal Reference Resistor

Connect a stable external resistance standard with a nominal value of 1Ω to

channel 1. Ideally, this should be a Wilkins resistor with a recent (traceable)

calibration certificate. Configure the microK to measure a Default PRT at 10mA

against the internal 1Ω reference on the 13Ω range on channel 1 (other channels

disabled). Use 1 sample per reading and 100 readings in the rolling statistics (see

section 3.6). Select the Single tab and clear the statistic. After the microK has

collected at least 100 readings (shown as Mean of last… in the Single tab, check

that the Mean agrees with the calibrated value of the resistance standard to within

2.5ppm (half of the specification limit) of the calibrated value and that the

standard deviation (S.D.) is less than 0.000005.

7.1.3 Voltage Measurements

The automatic input reversal of used by the microK when measuring voltage

provides good zero stability. However, small differences between the thermal

EMFs generated by the devices used to make these reversals on each channel

mean that the zero offset needs to be checked for each channel. Once the zeros

offsets have been checked/adjusted, it is only necessary to check the span on one

channel since this part of the measurement system is common to all the channels.

7.1.3.1 Zero Voltage Offsets

Short out the 4 measurement terminals on all 3 channels using a piece of un-

insulated copper wire (use pure copper wire to avoid generating unwanted

thermal EMFs) for each channel:

V I

Configure the microK to measure a Default Thermocouple on the 0.125V range

with units of Volts. Use 1 sample per reading and 100 readings in the rolling

statistics (see section 3.6). Select the Multi tab and clear the statistics for all 3

channels. After the microK has collected at least 100 readings (shown as Mean of

last… in the Multi tab, check that the Mean for each channels is less than

0.000000250 (0.25µV) and that the standard deviation (S.D.) is less than

0.000000050 (0.05µV).

7.1.3.2 Voltage Span Check

Connect a stable, low noise voltage source with a nominal value of 50mV to

channel 1 of the microK using low thermal EMF wire and connectors (copper or

an alloy such as tellurium–copper that has a high copper content and low thermal

EMF to pure copper. Brass connectors must NOT be used):

Voltage

Source

Configure the microK to measure a Default Thermocouple on the 0.125V range

with units of Volts. Use 1 sample per reading and 100 readings in the rolling

statistics (see section 3.6). Select the Single tab and clear the statistics. After the

microK has collected at least 100 readings (shown as Mean of last… in the Single

tab, check that the Mean value agrees with the applied voltage to within

0.000000250V (0.25µV) and that the standard deviation (S.D.) is less than

0.000000050V (0.05µV).

Repeat the procedure with the voltage source set to -50mV.

V I

7.2 Adjusting Calibration

This section describes the procedures for adjusting the internal reference

standards and the input offset voltages. These can be performed by the user or a

third party calibration provider, subject to the availability of the standards

specified below. Isothermal Technology additionally checks the temperature

coefficient of the zener reference and the linearity of the microK against an RBC

(resistance bridge calibration) with an uncertainty of 0.01ppm. We therefore

recommend that you return your microK to Isothermal Technology or one of its

appointed service centres annually for a comprehensive instrument calibration.

There are no potentiometers inside the microK to adjust, calibration is

implemented in software so can be performed without removing the cover from

your microK. Calibration is adjusted via the RS232 interface on the rear of the

microK. Connect the microK to a PC (using a 9-pin null-modem RS232 cable)

and establish an RS232 connection with it using Hyperterminal at 9,600 Baud

(for further details of how to connect a PC to your microK see section 8.1).

Confirm that the RS232 link is working by typing in *IDN? (terminate this and

all commands shown in this section by pressing the carriage return or enter key).

The microK will respond with a string in the form:

Isothermal Technology, microK 400,10-P190,firmware version 3.17

The calibration of your microK is password protected. Unlocked the calibration

to allow calibration adjustment using the command CAL:UNL password, where

password is the calibration system password (NOT necessarily the same as the

password used in the touch screen operator interface. The password is initially

set to “1234” but should be changed for security reasons (see section 10.4.33).

You can now use the SCPI commands (see section 10.4) detailed below to adjust

the microK’s calibration.

7.2.1 Calibrate Master Current Source

The microK’s current source has 3 ranges (0-0.1mA, 0-1mA and 0-10mA). The

tolerance between the ranges is sufficiently small that it is only necessary to

calibrate the 1mA range in order to achieve the full performance specification.

Connect a calibrated ammeter (or DMM) across the current terminals of channel

1 and connect both the sense inputs to the red current terminal:

V I

Send the command TEST:CURR 1 to your microK from Hyperterminal (this

forces the microK to source 1mA on channel 1). Measure the current and then

ST:CURR 10

9.975 to 10.025 mA

TEST:CURR

0.1 -

0.09975 to

0.10025 mA

TEST:CURR

-1 -0.9975 to

1.0025 mA

TEST:CURR

-10 -9.975 to

10.025 mA

ratio

type in the command CAL:CURR current , where current is the measured value.

Now type in TEST:CURR 1 again to update the current source. The ammeter

should now read 1mA ± 0.0003mA.

Check the other current ranges by typing in the following commands and

checking that the current is within the given limits:

command current limits

TEST:CURR 0.1 0.09975 to 0.10025 mA

7.2.2 Calibrating the 400 Ω Internal Reference Resistor

Connect a stable external resistance standard with a nominal value of 100Ω to

channel 1. Ideally, this should be a Wilkins resistor with a recent (traceable)

calibration certificate maintained at a constant temperature in an oil bath.

Configure the microK to measure a Default PRT at 1mA against the internal

400Ω reference on the 500Ω range with channel 1 (other channels disabled). Set

the units to ratio (Rt/Rs) with 1 sample per reading and 100 readings in the

rolling statistics (see section 3.6). Select the Single tab and clear the statistics.

After the microK has collected at least 100 readings (shown as Mean of last… in

the Single tab, record the Mean value and check that the standard deviation

(S.D.) is less that 0.000000100. Calculate the value of the internal resistor from:

R =400

referenceexernal

Adjust the value assigned to the internal 400Ω reference resistors by typing in

the command:

The value entered can be read back using CAL:REF205?.Check the new value

assigned to the internal 400Ω reference resistor (see section 7.1.2.2).

CAL:REF205 R400

7.2.3 Calibrating the 100 Ω Internal Reference Resistor

Repeat the procedure for calibrating the 400Ω internal reference (see section

7.2.2), but configure the microK to measure a Default PRT at 1mA against the

internal 100Ω reference on the 125Ω range with channel 1. The command to

adjust the value assigned to the 100Ω internal reference is:

CAL:REF204 R100

Where R100 is the value calculated for the 100Ω internal reference.

7.2.4 Calibrating the 25 Ω Internal Reference Resistor

Repeat the procedure for calibrating the 400Ω internal reference (see section

7.2.2), but configure the microK to measure a Default PRT at 1mA against the

internal 25Ω reference on the 125Ω range with channel 1. The command to

adjust the value assigned to the 25Ω internal reference is:

CAL:REF203 R25

Where R25 is the value calculated for the 25Ω internal reference.

7.2.5 Calibrating the 10 Ω Internal Reference Resistor

Connect a stable external resistance standard with a nominal value of 10Ω to

channel 1. Ideally, this should be a Wilkins resistor with a recent (traceable)

calibration certificate maintained at a constant temperature in an oil bath. Repeat

the procedure for calibrating the 400Ω internal reference (see section 7.2.2), but

configure the microK to measure a Default PRT at 5mA against the internal 10Ω

reference on the 25Ω range with channel 1. The command to adjust the value

assigned to the 10Ω internal reference is:

CAL:REF202 R10

Where R10 is the value calculated for the 10Ω internal reference.

7.2.6 Calibrating the 1 Ω Internal Reference Resistor

Connect a stable external resistance standard with a nominal value of 1Ω to

channel 1. Ideally, this should be a Wilkins resistor with a recent (traceable)

calibration certificate. Repeat the procedure for calibrating the 400Ω internal

reference (see section 7.2.2), but configure the microK to measure a Default PRT

at 10mA against the internal 1Ω reference on the 13Ω range on channel 1. The

command to adjust the value assigned to the 1Ω internal reference is:

CAL:REF201 R1

Where R1 is the value calculated for the 1Ω internal reference.

7.2.7 Calibrating Voltage Zeros

Short out the 4 measurement terminals on all 3 channels using a piece of un-

insulated copper wire (use pure copper wire to avoid generating unwanted

thermal EMFs) for each channel:

V I

Type in the following commands to remove the zero/offset correction for all

three channels:

CAL:OFFS1 0 CAL:OFFS2 0 CAL:OFFS3 0

Configure the microK to measure a Default Thermocouple on the 0.125V range

with units of Volts on all 3 channels. Use 1 sample per reading and 100 readings

in the rolling statistics (see section 3.6). Select the Multi tab and clear the

statistics for all 3 channels. After the microK has collected at least 100 readings

(shown as Mean of last… in the Multi tab, record the Mean for each channel and

check that the standard deviation (S.D.) is less that 0.000000050 (0.05µV).

Now adjust the zero offsets using the commands:

CAL:OFFS1 offset1 CAL:OFFS2 offset2 CAL:OFFS3 offset3

Where offsetX is the zero offset measured for channel X. The value entered for

each channel can be read back using CAL:OFFSX? (for channel X). Re-check the

zero offsets for all three channels (see section 7.1.3.1).

7.2.8 Calibrating Voltage Span

Connect a stable, low noise voltage source with a nominal value of 50mV to

channel 1 of the microK using low thermal EMF wire and connectors (copper or

an alloy such as tellurium–copper that has a high copper content and low thermal

EMF to pure copper. Brass connectors must NOT be used):

Voltage

Source

Configure the microK to measure a Default Thermocouple on the 0.125V range

with units of Volts. Use 1 sample per reading and 100 readings in the rolling

statistics (see section 3.6). Select the Single tab and clear the statistics. After the

microK has collected at least 100 readings (shown as Mean of last… in the

Single tab, record the Mean value and check that the standard deviation (S.D.) is

less than 0.000000050V (0.05µV).

Calculate the require gain from:

gain =

V I

valueactual

valuemeasured

Now apply the new gain by typing the command:

CAL:GAIN X40,POS,

gain

The value entered can be read back using CAL:GAIN? X40,POS

Repeat the procedure with the voltage source set to -50mV. Apply the new

negative polarity gain by typing in the command:

CAL:GAIN X40,NEG,

gain

The value entered can be read back using CAL:GAIN? X40,NEG

Pin Name

Function

1 CD carrier detect (not connected)

8 CTS

clear to send

9 - not used (not

connected)

Shell

frame ground (screen)

Parity Bit

none

8 RS232 Interface

The microK is equipped with an RS232 interface. This can be used to control the

microK and perform calibration and diagnostic functions. The command set uses

the SCPI (Standard Commands for Programmable Instruments) protocol (see

section 10 for details).

8.1 Establishing an RS232 Connection

The RS232 connector is located on the rear of your microK (see section 1.4). The

connector is a 9-way (male) D-type configured as a standard DTE device:

2 RD receive data 3 TD transmit data 4 DTR data terminal ready (fixed high) 5 SG signal ground 6 DSR data set ready (not connected) 7 RTS request to send

Connect your microK to a PC using a standard null-modem cable:

1 2 3 4 5 6 7 8 9

Shell

1 2 3 4 5 6 7 8 9

Shell

Null-Modem Cable

The format for the RS232 interface is as follows:

Baud Rate 9,600 Start Bits 1 Stop Bits 1

The microK has a 256-byte circular receive buffer. If the buffer becomes full, it

de-asserts RTS (connected to CTS on your PC through the null-modem cable) to

prevent further data being sent. If the PC continues to send data this will be

ignored (lost) until the microK has had time to make space in the buffer by

processing commands. The microK does not use its CTS to control data it

transmits.

You can use Hyperterminal (or another terminal emulator) to communicate with

the microK via the RS232 connection. Hyperterminal is part of the standard

Windows installation, usually located in the Accessories|Communications folder.

If you have installed a minimum (laptop) or custom configuration (without this

component) for your Windows operating system, you may need to install

Hyperterminal from your original Windows media.

Start Hyperterminal to setup a new connection. Type in a name for the

connection (such as microK) and select an icon. In the next window, select the

PC’s COM port to which you have connected your microK from the

using

drop-down list and click OK. In the next window, enter the data format for

Connect

the microK’s RS232 interface:

Click OK to open a Hyperterminal session with the microK. Now save (using

File:Save As) the Hyperterminal connection so that in future you only have to

click on this icon to open an RS232 connection with your microK.

Type *IDN? into Hyperterminal (terminate the command by pressing the

carriage return or Enter keys), the microK should then respond with a string in

the form:

Isothermal Technology, microK 400,10-P190,firmware version 3.17

This confirms that you have successfully established an RS232 connection with

your microK.

8 NDAC

Not Data Accepted

GND

Ground (paired with NDAC)

9 #IFC

Interface Clear

GND

Ground (paired with #IFC)

10 #SRQ

Service Request

GND

Ground (paired with #SRQ)

9 GPIB

The microK is equipped with an IEEE-488 GPIB (General Purpose Interface

Bus) port. This can be used to control the microK and perform calibration and

diagnostic functions. The command set uses the SCPI (Standard Commands for

Programmable Instruments) protocol (see section 10 for details).

The GPIB connector is located on the rear of your microK (see section 1.4). The

connector is the standard IEEE-488 connector (24-way):

Pin Name Function Pin Name Function

1 DIO1 Data Input/Output bit 13 DIO5 Data Input/Output bit 2 DIO2 Data Input/Output bit 14 DIO6 Data Input/Output bit 3 DIO3 Data Input/Output bit 15 DIO7 Data Input/Output bit 4 DIO4 Data Input/Output bit 16 DIO8 Data Input/Output bit 5 #EOI End or Identify 17 #REN Remote Enable 6 #DAV Data Valid 18 GND Ground (paired with #DAV) 7 NRFD Not Ready for Data 19 GND Ground (paired with NRFD)

11 #ATN Attention 23 GND Ground (paired with #ATN) 12 GND Shield 24 GND Logic Ground

Shell - Frame Ground (cable screen)

Unlike the RS232 interface (which is full duplex) the GPIB is inherently half-

duplex (data can only be transferred between the microK and the GPIB

Controller in one direction at any given time, this direction being determined by

the controller). If a response is expected from the microK, the GPIB Controller

must address the microK as a Talker in order that it can transmit this information.

The microK will try to send information on the GPIB for 2s, after which time it

will abandon attempts to respond and revert to being a Listener in order to

received further commands on the GPIB. This 2s window will start as soon as the

microK is ready to respond. There will be a delay from receiving the command

to attempting to respond depending on the command (requesting data involves a

short delay but requesting a measurement may take up to 2s) and whether the

microK is busy processing other commands (if measurements are being

requested via the front panel operator interface or via the RS232 interface).

The microK has a 254-byte receive buffer. If the command exceeds this length it

will be truncated.

9.1 GPIB Address

The microK behaves as a GPIB Peripheral and can have an address in the range 1

to 30 (inclusive). The factory default address is 10, but this can be changed

pressing

Port Settings

in the Instrument tab (see section 3.7.7):

9.2 Establishing a GPIB Connection

Connect your microK to a GPIB Controller using a standard (straight through)

GPIB cable. Send *IDN? to the GPIB address of the microK terminated with a

Line Feed (see section 10.1 for acceptable terminators), the microK should then

respond with a string in the form:

Isothermal Technology, microK 100,10-P190,firmware version 3.17

This confirms that you have successfully established a GPIB connection with

your microK.

10 SCPI Command Set

The command format and protocol used by the microK is based on the SCPI

(Standard Commands for Programmable Instruments) standard. This was

developed to provide a consistent command language for all types of

programmable instruments. The objective was to reduce the development time

required by users of these instruments by providing a consistent programming

environment through the use of defined messages, instrument responses and data

formats. Further information on SCPI can be obtained from the SCPI Consortium

(http://www.scpiconsortium.org).

10.1 Command Terminators

SCPI commands are ASCII (American Standard Code for Information

Interchange) character strings. If sent to the microK’s RS232 interface, these

should be terminated with a Carriage Return character (ASCII character 13).

Responses from the microK on the RS232 interface are always terminated by a

Carriage Return character.

If commands are sent to the microK’s GPIB port, they can be terminated by a

Line Feed character (ASCII 10), Carriage Return character (ASCII 13), EOI

condition (by pulling the #EOI line low during the last character of the ASCII

string) or any combination of these. Responses from the microK on the GPIB

interface are always terminated by a Line Feed character (the microK does not

assert EOI at the end of a response).

10.2 SCPI Command Structure

Commands are arranged in a hierarchical tree, similar to directory trees used in

personal computers. SCPI uses a defined notation to represent the command tree

structure. Each node in the tree structure is a command keyword with keywords

being separated by colons (:). To simplify the description of the SCPI commands,

the notation represents levels in the tree using horizontal indentations with the

root node being the left most column. For example, the microK includes the

following command structure:

SENSe :FUNCTION :CHANNEL :FREsistance :REFerence :REFerence? :RANGe :RANGe? READ?

CALibrate :CURRent :OFFSet :OFFSet?

A valid command is formed by following the tree structure from a root node until

a node is reached with no further nodes below it, for example in the above

command tree we may use:

SENSe:FRESistance:REFerence

Keywords can be shortened to the first four letters (or 3 if the last letter is a

vowel). To indicate this, the notation uses upper-case to indicate required letters

and lower-case to indicate optional letters (NB: all commands are case-

insensitive). For example, valid forms of the above command include:

Sense:Fresistance:Reference SENS:FRES:REF Sense:fresistance:REF

To shorten the commands, default (optional) keywords are enclosed in square

brackets and may be omitted. For example, in the case of the command:

MEASure[:SCALar]:VOLTage:[DC]?

Valid forms of this command include:

MEAS:VOLT? MEASURE:SCALAR:VOLTAGE:DC?

channel#

Internal reference resistor

201 1 Ω

10.2.1 SCPI Numeric Suffices

In order to support multiple input channels, commands can include numeric

suffices. These are represented by a hash (#) in the command notation, for

example:

MEASure:VOLTage:<channel#>?

In addition to the 3 input channels on the front panel (which are assigned the

suffices 1, 2 and 3) the internal reference resistors are specified using numeric

suffices as follows:

202 10 Ω 203 25 Ω 204 100 Ω 205 400 Ω

In order to measure the voltage on channel 3, the command used would be:

MEAS:VOLT3?

10.2.2 Parameters

If a command requires parameter(s), these follow the command and are separated

from it by a space. If more than one parameter is required, each parameter is

separated by a comma (,). For example, the command to measure a four-terminal

resistance on channel 1 against a reference resistor on channel 2 using the 100

ohm range and a sense current of 1mA would be:

MEAS:FRES1:REF2? 100,1

10.2.3 Units

Numeric parameters may optionally include units. The standard multiplying

prefixes may also be used to indicate decimal multiples or fractions. For

example, the following are all equivalent.

CURRENT 0.001A CURRENT 1ma

CURRENT 1000UA CURRENT 1

The following prefixes are available:

prefix name factor

N or n nano 10

-9

U or u micro 10-6 M or m milli 10-3 K or k kilo 10+3 MA or ma mega 10

10.3 Making Measurements using SCPI Commands

The microK’s measurement system is controlled by a microprocessor connected

to the rear panel RS232 interface and a GPIB port. The measurement system can

be controlled by SCPI commands from either of these. The firmware makes no

distinction between commands received on the RS232 interface and those from

the GPIB and will process these in the order in which they are detected. If a

response is expected, it will always be sent on the interface (RS232 or GPIB) on

which the corresponding command was sent.

There is no direct interference between measurements made using the front panel

operator interface and measurements requested using SCPI commands. However,

measurements take some time to complete so there may be a delay in responses

to SCPI commands if measurements are being made via the front panel operator

interface. To avoid unnecessary delays to responses to SCPI commands, you can

stop all measurements requested via the front panel operator interface. The

easiest way to do this is to restart the microK and then not press

Resume

in the

opening window. The main application that provides the user interface will then

not start and no measurements will be requested.

10.3.1 Measuring Resistance using SCPI Commands

In order to measure the resistance of a PRT, you need to:



set the microK to measure resistance



set the sense current



select the measurement range



select the measurement channel



select the reference channel



make the measurement

If you want to measure a 25.5Ω SPRT up to a maximum resistance of 30Ω

against the internal 100Ω reference, the maximum resistance that the

measurement system sees is 100Ω. To make this measurement using a 1mA

sense current, you can use the following command sequence:

SENS:FUNC FRES CURR 1 SENS:FRES:RANG 100,1

SENS:CHAN 1

SENS:FRES:REF 204

READ?

The microK will then report the measured resistance, for example

“2.5250637862E001”.

The following command performs the same measurement:

MEAS:FRES1:REF204? 100,1

10.3.2 Measuring Voltage using SCPI Commands

In order to measure the voltage from a thermocouple, you need to:



set the microK to measure voltage



select the measurement range



select the measurement channel



make the measurement

If you want to measure the voltage from a thermocouple, you should always use

the most sensitive voltage range (0.125V) since this provides the lowest

uncertainty and no thermocouple output will exceed this range. You can use the

following command sequence:

SENS:FUNC VOLT

SENS:VOLT:RANG 0.1

SENS:CHAN 1

READ?

The microK will then report the measured voltage, for example “1.12999999E-

007”.

The following command performs the same measurement:

MEAS:VOLT1? 0.1

10.4 SCPI Commands

The microK supports the following commands:

*IDN? *RST SENSe :FUNCtion[:ON] :FUNCtion[:ON]? :CHANnel :CHANnel? :VOLTage[:DC] :RANGe[:UPPer] :RANGe[:UPPer]? :FRESistance

:REFerence :REFerence? :RANGe[:UPPer] :RANGe[:UPPer]? :RATio

:REFerence :REFerence? :RANGe[:UPPer] :RANGe[:UPPer]? INITiate[:IMMediate][:ALL] FETCh[:SCALar]? READ[:SCALar]? READ<channel#>? MEASure[:SCALar]

:VOLTage[:DC]<channel#>?

:FRESistance<channel#>

:REFerence<reference#>? :RATio<channel#>

:REFerence<reference#>? [:SOURce]:CURRent TEST :CURRent CALibrate :CURRent

:REFerence<reference#> :REFerence<reference#>? :OFFSet<channel#> :OFFSet<channel#>? :GAIN :GAIN? :PASSword :UNLock :LOCK

< denominator channel>

A detailed description of each command follows:

10.4.1 Command: *IDN?

Format: *IDN?

Reports information on the microK in 4 comma separated fields:



manufacturer



model



serial number



firmware version

Example: for a microK 400 with serial number 261067/1 using firmware version

1.20, the microK responds to *IDN? with:

Isothermal Technology,microK 400,261067/1,firmware version 1.20

10.4.2 Command: *RST

Format: *RST

Performs a reset (equivalent to a power-on reset) of the measurement system

firmware.

10.4.3 Command: SENSe:FUNCtion

Format: SENSe:FUNCtion

Selects the measurement function. The parameter

following valid SCPI parameters:



VOLTage[:DC]



FRESistance



RATio

Example: to set the microK to measure ratio, use: SENS:FUNC RAT

must be one of the

10.4.4 Command: SENSe:FUNCtion?

Format: SENSe:FUNCtion?

Reports the current measurement function.

Example: a microK set to measure voltage will respond to SENS:FUNC? with

“VOLTAGE”.

10.4.5 Command: SENSe:CHANnel

Format: SENSe:CHANnel

Selects the channel for the next measurement. The channel is not actually

selected until a measurement is started using with either the INITiate or READ?

commands.

Example: to select channel 2 for the next measurement, use: SENS:CHAN 2

10.4.6 Command: SENSe:CHANnel?

Format: SENSe:CHANnel?

Reports the channel selected for the next measurement.

Example: a microK set to measure channel 1 on the next measurement will

respond to SENS:CHAN? with: “1”.

10.4.7 Command: SENSe:VOLTage:RANGe

Format: SENSe[:DC]:VOLTage:RANGe[:UPPER]

Sets the range for the next voltage measurement. There are 3 voltage ranges

available in the microK:



0 – 0.125V



0 - 0.5V



0 - 2.5V

If you enter a numeric value other than one of the above, the microK will round

the value up to the next available range. Always use the most sensitive range

possible to minimise uncertainties. Therefore, when measuring thermocouples

always use the 0.125V range.

Example: to set the microK to measure a thermocouple that has a maximum

output voltage of 20mV, use: SENS:VOLT:RANG 20mV. This will set the

microK to the 125mV range.

10.4.8 Command: SENSe:VOLTage:RANGe?

Format: SENSe[:DC]:VOLTage:RANGe[:UPPER]?

Reports the range for the next voltage measurement (0.125, 0.5 or 2.5)

Example: a microK that has had its voltage range set using the command shown

in section 10.4.7) would respond to the command: SENS:VOLT:RANG? with:

“0.125”.

10.4.9 Command: SENSe:FRESistance:REFerence

Format: SENSe:FRESistance:REFerence

Selects the reference channel for the next resistance measurement made. The

channel is not actually selected until a measurement is started using with either

the INITiate or READ? commands.

Example: to select channel 204 (internal 100 ohm resistor) as the reference

channel for the next resistance measurement, use: SENS:FRES:REF 204

10.4.10 Command: SENSe:FRESistance:REFerence?

Format: SENSe:FRESistance:REFerence?

Reports the channel selected as the reference channel for the next resistance

measurement.

Example: a microK set to use channel 204 as the reference in the next resistance

measurement will respond to the command SENS:FRES:REF? with: “204”.

10.4.11 Command: SENSe:FRESistance:RANGe

Format: SENSe:FRESistance:RANGe[:UPPer]

Sets the range for the next resistance measurement. The range is determined by

the voltage range of the measurement system (0.125, 0.5 or 2.5V) and depends

on the sense current used. The

in the measurement, this may not be the same as the present value of sense

current that is set with the CURRent command. The 3 resistance ranges available

with the microK are:

current

parameter is the current you intend to use



resistance range = 0.125V / current



resistance range = 0.5V / current



resistance range = 2.5V / current

The resistance range specified should be the higher of the maximum PRT

resistance and reference resistor since the measurement system has to measure

the signal across both to determine the resistance of the device under test.

Example: to set the microK to measure a PRT that has a maximum resistance of

130Ω (using a 100Ω reference resistor) with a 1mA sense current, use:

SENS:FRES:RANG 130,1. This will set the microK to the middle range.

10.4.12 Command: SENSe:FRESistance:RANGe?

Format: SENSe:FRESistance:RANGe[:UPPer]?

Reports the range for the next resistance measurement at the present sense

current (set using the CURRent command). The current used to calculate the

range may be different from that specified when the range was set using the

SENSe:FRESistance:RANGe command. The reported range is the actual range

for the measurement system at the present sense current.

Example: a microK that has had its resistance range set using the command

shown in section 10.4.11 but has its sense current set to 10mA would respond to

the command: SENS:FRES:RANG? with: “50.000000”.

10.4.13 Command: SENSe:RATio:REFerence

Format: SENSe:RATio:REFerence

Selects the reference channel for the next resistance ratio measurement made.

The channel is not actually selected until a measurement is started using with

either the INITiate or READ? commands.

Example: to select channel 2 as the reference channel for the next resistance ratio

measurement, use: SENS:RAT:REF 2

10.4.14 Command: SENSe:RATio:REFerence?

Format: SENSe:RATio:REFerence?

Reports the channel selected as the reference channel for the next resistance ratio

measurement.

Example: a microK set to use channel 2 as the reference in the next resistance

ratio measurement will respond to the command SENS:RAT:REF? with: “2”.

10.4.15 Command: SENSe:RATio:RANGe

Format: SENSe:RATio:RANGe[:UPPer]

Sets the range for the next resistance ratio measurement. The range is determined

by the voltage range of the measurement system (0.125, 0.5 or 2.5V) and

depends on the sense current used. The

current

parameter is the current you

intend to use in the measurement, this may not be the same as the present value

of sense current that is set with the CURRent command. The 3 resistance ranges

available with the microK are:



resistance range = 0.125V / current



resistance range = 0.5V / current



resistance range = 2.5V / current

The resistance range specified should be the higher of the maximum PRT

resistance and reference resistor since the measurement system has to measure

the signal across both to determine their ratio.

Example: to set the microK to measure the resistance ratio of a PRT that has a

maximum resistance of 130Ω (with a 100Ω reference resistor) with a 1mA sense

current, use: SENS:RAT:RANG 130,1. This will set the microK to the middle

range.

10.4.16 Command: SENSe:RATio:RANGe?

Format: SENSe:RATio:RANGe[:UPPer]?

Reports the range for the next resistance ratio measurement at the present sense

current (set using the CURRent command). The current used to calculate the

range may be different from that specified when the range was set using the

SENSe:RATio:RANGe command. The reported range is the actual range for the

measurement system at the present sense current.

Example: a microK that has had its resistance ratio range set using the command

shown in section 10.4.15 but has its sense current set to 10mA would respond to

the command: SENS:RAT:RANG? with: “50.000000”.

10.4.17 Command: INITiate

Format: INITiate[:IMMediate][:ALL]

Initiates a measurement using the conditions defined by previous SENSe

commands. The measurement is made immediately, but not reported.

Example: to initiate a voltage measurement that has been defined with SENSe

commands (such as SENS:CHAN 1, SENS:FUNC volt and SENS:VOLT:RANG

0.1) use: INIT

10.4.18 Command: FETCh?

Format: FETCh[:SCALar]?

Reports the result of the last measurement made.

Example: a microK that has made a measurement on a short circuit connected to

channel 1 using the commands shown in the example in section 10.4.17 will

respond to FETC? with something similar to : “1.70000000E-008”.

10.4.19 Command: READ?

Format: READ[:SCALar]?

Initiates and reports a measurement using the conditions defined by previous

SENSe commands. This is equivalent to INIT followed by FETCh?

Example: a microK that is connected to a short circuit on channel 1 and has been

configured to make a voltage measurement using SENSe commands (such as

SENS:CHAN 1, SENS:FUNC volt and SENS:VOLT:RANG 0.1) will respond to

READ? with something similar to : “1.70000000E-008”.

10.4.20 Command: READ#?

Format: READ<channel#>?

Reports the next measurement and units on <channel#> made using the front

panel operator interface. It is the only command that allows the user to access

results in temperature units. Unlike other commands, where it is recommended

that the operator interface is left dormant (Resume not pressed to speed up

measurements) the operator interface MUST be running (measurements being

made) in order for this command to function.

Example: a user who is making temperature measurements on channel 1 using an

SPRT (see section 2.1) can read the temperature measurements by sending

READ1? The microK will respond with something similar to “1.23456789,C”.

The units are reported using:

X = Ratio R = Ohms V = Volts K = Kelvin C = Celsius F = Fahrenheit

If the requested channel does not exist or is not enabled, the microK will respond

with “not enabled,X”.

10.4.21 Command: MEASure:VOLTage?

Format: MEASure[:SCALar]:VOLTage[:DC]<channel#>?

Initiates and reports a voltage measurement on <channel#> using the voltage

range specified (note that there is no gap between the command and the channel

number as this command makes use of the numeric suffices feature of SCPI

described in section 10.2.1). This command is equivalent to SENS:FUNC volt,

SENS:CHAN

, SENS:VOLT:RANG

The voltage range specified is rounded up to the nearest available range.

Example: to initiate a voltage measurement on channel 3 using the 0.125V range

use: MEAS:VOLT3 0.125

and READ?

10.4.22 Command: MEASure:FRES:REF?

Format: MEASure[:SCALar]:FRESistance<channel#>:REFerence<reference#>?

Initiates and reports a resistance measurement on <channel#> against a reference

on channel <reference#> using <resistance range> with sense <current> (note

that there is no gap between the command and the channel numbers as this

command makes use of the numeric suffices feature of SCPI described in section

10.2.1). This command is equivalent to SENS:FUNC fres, SENS:FRES:REF

<reference#>

SENS:CHAN

, SENS:FRES:

and READ?

RANG <resistance range>,<current>

Example: to set the microK to measure a PRT on channel 1 that has a maximum

resistance of 130Ω using the internal 100Ω reference resistor with a 1mA sense

current, use: MEAS:FRES1:REF204? 130,1

10.4.23 Command: MEASure:RAT:REF?

Format: MEASure[:SCALar]:RATio<channel#>:REFerence<reference#>?

Initiates and reports a resistance ratio measurement on <channel#> against a

reference on channel <reference#> using <resistance range> with sense

<current> (note that there is no gap between the command and the channel

numbers as this command makes use of the numeric suffices feature of SCPI

described in section 10.2.1). This command is equivalent SENS:FUNC rat,

SENS:RAT:REF

range>,<current>

<reference#>

, SENS:CHAN

, SENS:RAT:

RANG <resistance

and READ?

Example: to set the microK to measure the resistance ratio of a PRT on channel 1

that has a maximum resistance of 130Ω against a 100Ω reference resistor on

channel 2 with a 1mA sense current, use: MEAS:RAT1:REF2? 130,1

10.4.24 Command: CURRent

Format: [SOURce]:CURRent

Set the sense current for the next resistance or ratio measurement to

The current is not changed until a measurement is started using with either the

INITiate or READ? commands.

Example: to set the sense current for the next resistance measurement to 2mA

use: CURR 2

10.4.25 Command: TEST:CURRent

Format: TEST:CURRent

Immediately sets the sense current on channel 1 to <

Example: to set the sense current on channel 1 to 5mA use: TEST:CURR 5

current>

10.4.26 Command: CALibrate:CURRent

Format: CALibrate:CURRent

This command is used after using the TEST:CURR 1 command and measuring

the current from channel 1 (see section 7.2.1). It uses the actual current entered to

adjust the master current source the correct current.

Example: the current from channel 1 after using the command TEST:CURR 1

was measured as 1.00123. To adjust the master current source correctly use:

CAL:CURR 1.00123

10.4.27 Command: CALibrate:REFerence

Format: CALibrate:REFerence<reference#>

Used to calibrate the internal <

resistance>

resistor are given in section 10.2.1. The calibrated value is stored as a floating

point number and will therefore be subject to some rounding (less than 0.12ppm

of value)

Example: if the value of the internal 100Ω reference has been measured as

100.00123, the new value can be assigned to it using: CAL:REF204 100.00123

to it. The channel numbers (numeric suffices) used for the internal

reference#>

standard by assigning a new

<actual

10.4.28 Command: CALibrate:REFerence?

Format: CALibrate:REFerence<reference#>?

Used to report the calibrated value of the internal <reference#> resistor (used by

the microK to calculate resistance).

Example: a microK with an internal 25Ω reference having a calibrated value of

25.01234 will respond to CAL:REF203 with “25.01234”

10.4.29 Command: CALibrate:OFFSet

Format: CALibrate:OFFSet<channel#> <offset>

Adjusts the voltage offset for

<channel#>

used when making voltage

measurements. The offset range is ±2µV, attempts to apply an offset greater than

this will be ignored. The offset is stored as a floating point number and will

therefore be subject to some rounding (less than 0.12ppm of value)

Example: to subtract an offset of 0.123µV from voltages measured on channel 3

use: CAL:OFFS3 0.123

10.4.30 Command: CALibrate:OFFSet?

Format: CALibrate:OFFSet<channel#>?

Reports the offset subtracted from voltage measurements on

Example: a microK that has been calibrated to have a 0.123µV offset subtracted

from voltage measurement on channel 2 will respond to CAL:OFFS2? with

“1.23E-07”.

<channel#>

10.4.31 Command: CALibrate:GAIN

Format: CALibrate:GAIN

Adjusts the value of <gain> for <polarity> by the factor <adjustment>. The

parameter <gain> must be one of three strings defining the nominal gain of the

microK pre-amplifier:



X10



X40

The parameter <polarity> must be either POSitive or NEGative.

The gain adjustment is stored as a floating point number and will therefore be

subject to some rounding (less than 0.12ppm of value)

Example: for a microK that has been found to have a voltage gain for positive

readings on its x40 range that is low by a factor of 1.000123 (see section 7.2.8),

the gain can be corrected using: CAL:GAIN X40,POS,1.000123

10.4.32 Command: CALibrate:GAIN?

Format: CALibrate:GAIN?

Reports the total calibration adjustment applied to the voltage <gain> range. The

parameter <gain> must be one of three strings defining the nominal gain of the

microK pre-amplifier:



X10



X40

The parameter <polarity> must be either POSitive or NEGative.

Example: a microk that has had a number of adjustments to its nominal x40 gain

causing a total ratio adjustment of 1.000123 for positive readings will respond to

CAL:GAIN? X40,POS with “1.000123”

10.4.33 Command: CALibrate:PASSword

Format: CALibrate:PASSword

Changes the password used to lock (protect) the calibration of the microK’s

measurement system. This is initially set to “1234”, but should be changed

before using the microK for any critical or traceable measurement or calibration

work. The new password must be at least 4 characters in length and must be

typed in identically twice in order to effect the change.

Example: to change the password from 1234 to ABCD use: CAL:PASS

1234,ABCD,ABCD

10.4.34 Command: CALibrate:UNLock

Format: CALibrate:UNLock

Unlocks the microK to allow calibration adjustment. The microK always powers

up in the locked state. Calibration can be re-locked by re-powering the microK or

using CAL:LOCK (see section 10.4.35).

Example: to unlock (enable) the calibration adjustment on a microK with the

default password (“1234”), use: CAL:UNL 1234

10.4.35 Command: CALibrate:LOCK

Format: CALibrate:LOCK

Locks the microK to prevent calibration adjustment.

Example: to lock the calibration of a microK after adjustment, use: CAL:LOCK

11 Specification

Ranges Resistance Thermometers: 0Ω to 500k Ω

Thermocouples: ±125mV

Accuracy –

PRTs

µK400: 0.4ppm maximum over whole range for SPRT

with R0 ≥ 2.5Ω (equivalent to 0.1mK at 0°C, or 0.4mK over full range) 1ppm maximum over whole range for SPRT with R0=0.25Ω

µK800: 0.8ppm maximum over whole range for SPRT

with R0 ≥ 2.5Ω (equivalent to 0.2mK at 0°C, or 0.8mK over full range) 2ppm maximum over whole range for SPRT with R0=0.25Ω

Accuracy –

Thermocouples

Voltage uncertainty: 250nV (between 0 and 20mV)

equivalent to 0.01°C for Gold-Platinum thermocouple at 1000°C

Resolution Resistance: 0.01ppm of range

Voltage: 2nV (125mV range)

Stability Resistance (excluding resistance standard): 0 (note1)

Voltage: 3ppm/year

Measurement

Time

Temperature

Conversions

Resistance: < 2s (1s using the RS232 or GPIB interfaces)

Voltage: < 1s (0.5s using the RS232 or GPIB interfaces)

PRTs: ITS-90, Callendar-van Dusen

Thermocouples: IEC584-1 1995 (B,E,J,K,N,R,S,T), L and

gold-platinum

Thermistors: Steinhart-Hart

Sensor Current 0-10mA in 3 ranges:

0.1mA ±0.4% of value, ±70nA, resolution 28nA

1mA ±0.4% of value, ±0.7µA, resolution 280nA

10mA ±0.4% of value, ±7µA, resolution 2.8µA

Keep-Warm

Current

Cable Length

Internal

Standard

Resistors

0-10mA ±0.4% of value, ±7µA, resolution 2.8µA

<30m (maximum 10Ω per core or 10nF shunt capacitance)

1Ω ±0.1% TCR = ±0.6ppm/°C typical, stability ±5ppm/year

10Ω ±0.1% TCR = ±0.6ppm/°C typical, stability = ±5ppm/year

25, 100, 400 Ω ±0.1% TCR = ±0.3ppm/°C typical, stability = ±5ppm/year

Input

Connectors

“Cable Pod” connectors for: 4mm plugs, spades or bare wires

Contact material: gold plated tellurium copper

Interfaces RS232 (9,600 baud)

GPIB

USB (1.1) – host

Display 163mm / 6.4” VGA (640 x 480) colour TFT LCD

Operating

Conditions

15-30°C / 50-85°F, 10-90% RH (for full specification)

0-40°C / 32-105°F, 0-99% RH (operational)

Power 88 – 264V (RMS), 47-63Hz (Universal)

20W maximum, 1.5A (RMS) maximum

Size 520mm x 166mm x 300mm / 20.5” x 6.6” x 11.9” (W x D x H)

Weight 12.4kg / 27lb

Notes:

1. The microK uses a ‘substitution technique’ in which the DeviceUnder-Test and the Reference are successively switched into the same position in the measuring circuit. This means that the stability of resistance ratio measurements is immeasurably small (see section 6.2)

12 Approvals

The microK has been independently verified as complying with the regulatory

requirements of the EU and FCC for electromagnetic compatibility and safety

(EU only).

12.1 CE Declaration

European Community Electromagnetic Compatibility Directive (89/336)

European Community Low Voltage Directive (93/68)

The microK Precision Thermometry Bridge manufactured by Isothermal

Technology Limited of Pine Grove, Southport, Merseyside, PR9 9AG, United

Kingdom conforms to the requirements of the European Community

Electromagnetic Compatibility Directive (89/336) and of the European

Community Low Voltage Directive (93/68).

12.2 FCC Statement

This equipment has been tested and found to comply with the limits for a Class A

digital device, pursuant to part 15 of the FCC Rules. These limits are designed to

provide reasonable protection against harmful interference when the equipment

is operated in a commercial environment. This equipment generates and can

radiate radio frequency energy and, if not installed and used in accordance with

the instruction manual, may cause harmful interference to radio communications.

Operation of this equipment in a residential area may cause harmful interference,

in which case the user will be required to correct the interference at his own

expense. Changes or modifications to this equipment not expressly approved by

Isothermal Technology could degrade EMC performance and void the user’s

authority to operate the equipment.

12.3 Standards Applied

The following standards have been applied in assessing compatibility with the

requirements for CE marking and for FCC compliance:

Conducted Emissions EN61326:1997 & CFR47:2005 Radiated Emissions EN61326:1997 & CFR47:2005 Conducted Immunity EN61326:1997 Radiated Immunity EN61326:1997 Electrical Fast Transients EN61326:1997 Electrostatic Discharge EN61326:1997 Surge EN61326:1997 Voltage Dips & Interruptions EN61326:1997 Harmonic Currents EN61000-3-2:2000 Flicker EN61000-3-3:1995 Electrical Safety EN61010-1:2001

Isotech microK-400, micro-800 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual