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Isotech microK-400 User Manual

Thermometry instruments
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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

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  • Page 1 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 info@microk.co.uk W: www.microk.co.uk...

  • Page 2: Table Of Contents

    CONTENTS INTRODUCTION ................6 Unpacking ..........................7 Safety ............................. 7 Powering Up Your microK ....................9 A Quick Tour of Your microK ................... 9 MAKING A MEASUREMENT (TUTORIALS) ........12 Measuring Temperature with a Calibrated SPRT ............12 Measuring Temperature with a Thermocouple .............. 16 DRIVING YOUR MICROK ...............
  • Page 3 CONNECTING THERMOMETER SENSORS ......... 43 The “Cable-Pod” Connectors ................... 43 Connecting PRTs (4-wire) ....................43 Connecting PRTs (3-wire) ....................44 Connecting PRTs (2-wire) ....................44 Connecting Thermocouples (external Ice Point or WTP) ..........45 Connecting Thermocouples (using RJ compensation) ........... 46 Connecting Thermistors ....................
  • Page 4 7.2.3 Calibrating the 100 Internal Reference Resistor ......66 7.2.4 Calibrating the 25 Internal Reference Resistor ......66 7.2.5 Calibrating the 10 Internal Reference Resistor ......66 7.2.6 Calibrating the 1 Internal Reference Resistor ......66 7.2.7 Calibrating Voltage Zeros ............. 67 7.2.8 Calibrating Voltage Span ..............
  • Page 5 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...

  • Page 6: Introduction

    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).

  • Page 7: Unpacking

    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.
  • Page 8 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...

  • Page 9: Powering Up Your Microk

    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.
  • Page 10 Input Touch Screen & Display Connector Terminals 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.
  • Page 11 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.

  • Page 12: Making A Measurement (Tutorials)

    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...
  • Page 13 Before making any measurement, you will have to enter information about the thermometer into the microK’s database. When the main window opens, press tab: Instrument 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 –...
  • Page 14 Press Coefficients to open the coefficients window. Press the ellipses buttons to enter the calibration data for the thermometer from its calibration certificate: Press to close the coefficients window and press 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...
  • Page 15 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).

  • Page 16: Measuring Temperature With A Thermocouple

    Press 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: ©...
  • Page 17 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...
  • Page 18 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).
  • Page 19 Press 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: © Page 19 of 97 Issue: 1.04...

  • Page 20: Driving Your Microk

    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.

  • Page 21: The Main Window

    “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.

  • Page 22: The Single Tab

    All functions to control the microK are available in this Window, which is divided into four tabs: displays a single channel in numeric and graphical form Single displays all three channels in numeric form Multi allows you to configure the channels to perform the Settings required measurement allows you to enter information on the thermometers and...
  • Page 23 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.
  • Page 24 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 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).

  • Page 25: The Multi Tab

    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.

  • Page 26: The Settings Tab

    Clear buttons: Press the button to clear (reset) the statistics for each Clear 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.
  • Page 27 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.
  • Page 28 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.
  • Page 29 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.
  • Page 30 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.

  • Page 31: The Instrument Tab

    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.
  • Page 32 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.
  • Page 33 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.

  • Page 34: Edit Resistors

    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.

  • Page 35: Calibration

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

  • Page 36: Update Software

    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.

  • Page 37: Port Settings

    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.

  • Page 38: Set Date And Time

    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.

  • Page 39: Clear Data Files

    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.

  • Page 40: Using The Thermometer Database

    “DiskOnChip” (solid state drive) memory or an USB flash drive. Press External the required button and then use the up/down buttons to select the required configuration. Press to load the configuration, or press to close the Cancel 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.

  • Page 41: Using The Reference Resistors Database

    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.

  • Page 42: Password Protection Of Key Settings

    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.

  • Page 43: Connecting Thermometer Sensors

    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.

  • Page 44: Connecting Prts (3-Wire)

    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’...

  • Page 45: Connecting Thermocouples (External Ice Point Or Wtp)

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

  • Page 46: Connecting Thermocouples (Using Rj Compensation)

    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...
  • Page 47 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.

  • Page 48: Good Practice Guidelines

    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.
  • Page 49 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 25 SPRT a 1mK temperature uncertainty corresponds to 100µ resistance uncertainty.
  • Page 50 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’...

  • Page 51: The Microk Technology

    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’.
  • Page 52 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.

  • Page 53: Substitution Topology

    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-∆...
  • Page 54 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.

  • Page 55: Minimising Thermal Emfs

    Resistor SPRT Reference Amplifier Guard 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.

  • Page 56: Solid-State Switching

    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.

  • Page 57: Eliminating Self-Heating Effects

    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.

  • Page 58: Calibration

    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).

  • Page 59: Resistance Measurements

    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...

  • Page 60: Internal Reference Resistor

    4-Terminal Short-Circuit Configure the microK to measure a Default PRT at 1mA against the internal 100 reference on the 125 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).

  • Page 61: Internal Reference Resistor

    7.1.2.3 100 Internal Reference Resistor Repeat the procedure for checking the 400 internal reference (see section 7.1.2.2), but configure the microK to measure a Default PRT at 1mA against the internal 100 reference on the 125 range on channel 1. 7.1.2.4 25 Internal Reference Resistor Repeat the procedure for checking the 400 internal reference (see section...

  • Page 62: Voltage Measurements

    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.

  • Page 63: Adjusting Calibration

    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).

  • Page 64: Calibrate Master Current Source

    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).

  • Page 65: Calibrating The 400 Internal Reference Resistor

    type in the command CAL:CURR current , where is the measured value. current 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...

  • Page 66: Calibrating The 100 Internal Reference Resistor

    7.2.3 Calibrating the 100 Internal Reference Resistor Repeat the procedure for calibrating the 400 internal reference (see section 7.2.2), but configure the microK to measure a Default PRT at 1mA against the internal 100 reference on the 125 range with channel 1. The command to adjust the value assigned to the 100 internal reference is: CAL:REF204 R100 Where R100 is the value calculated for the 100 internal reference.

  • Page 67: Calibrating Voltage Zeros

    calibration certificate. Repeat the procedure for calibrating the 400 internal reference (see section 7.2.2), but configure the microK to measure a Default PRT at 10mA against the internal 1 reference on the 13 range on channel 1. The command to adjust the value assigned to the 1 internal reference is: CAL:REF201 R1 Where R1 is the value calculated for the 1 internal reference.

  • Page 68: Calibrating Voltage Span

    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...
  • Page 69 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 ©...

  • Page 70: Rs232 Interface

    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).
  • Page 71 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.
  • Page 72 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.

  • Page 73: Gpib

    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).

  • Page 74: Gpib Address

    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):...

  • Page 75: Scpi Command Set

    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.
  • Page 76 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...

  • Page 77: Scpi Numeric Suffices

    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: channel#...
  • Page 78 CURRENT 1000UA CURRENT 1 The following prefixes are available: prefix name factor N or n nano U or u micro M or m milli K or k kilo MA or ma mega © Page 78 of 97 Issue: 1.04...

  • Page 79: Making Measurements Using Scpi Commands

    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.

  • Page 80: Measuring Voltage Using Scpi Commands

    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...

  • Page 81: Scpi Commands

    10.4 SCPI Commands The microK supports the following commands: *IDN? *RST SENSe :FUNCtion[:ON] <function> :FUNCtion[:ON]? :CHANnel <channel> :CHANnel? :VOLTage[:DC] :RANGe[:UPPer] <voltage range> :RANGe[:UPPer]? :FRESistance :REFerence <reference channel> :REFerence? :RANGe[:UPPer] <resistance range>,<current> :RANGe[:UPPer]? :RATio :REFerence < denominator channel> :REFerence? :RANGe[:UPPer] <resistance range>,<current> :RANGe[:UPPer]? INITiate[:IMMediate][:ALL] FETCh[:SCALar]?

  • Page 82: Command: *Idn

    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...

  • Page 83: Command: Sense:channel

    Example: a microK set to measure voltage will respond to SENS:FUNC? with “VOLTAGE”. 10.4.5 Command: SENSe:CHANnel Format: SENSe:CHANnel <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.

  • Page 84: Command: Sense:voltage: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”.

  • Page 85: Command: Sense:fresistance:range

    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.

  • Page 86: Command: Sense:ratio:range

    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] <resistance range>,<current>...

  • Page 87: Command: Initiate

    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.

  • Page 88: Command: Measure:voltage

    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.

  • Page 89: Command: Measure:rat:ref

    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).

  • Page 90: Command: Test:current

    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 <current> Immediately sets the sense current on channel 1 to < current> . Example: to set the sense current on channel 1 to 5mA use: TEST:CURR 5 10.4.26 Command: CALibrate:CURRent...

  • Page 91: Command: Calibrate:offset

    Used to report the calibrated value of the internal <reference#> resistor (used by the microK to calculate resistance). Example: a microK with an internal 25 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#>...

  • Page 92: Command: Calibrate:gain

    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...

  • Page 93: Command: Calibrate:lock

    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...

  • Page 94: Specification

    11 Specification Ranges Resistance Thermometers: 0 to 500k Thermocouples: ±125mV Accuracy – µK400: 0.4ppm maximum over whole range for SPRT with R ≥ 2.5 (equivalent to 0.1mK at 0° C, or 0.4mK over PRTs full range) 1ppm maximum over whole range for SPRT with =0.25 µK800: 0.8ppm maximum over whole range for SPRT...
  • Page 95 Keep-Warm 0-10mA ±0.4% of value, ±7µA, resolution 2.8µA Current Cable Length <30m (maximum 10 per core or 10nF shunt capacitance) Internal ±0.1% TCR = ±0.6ppm/° C typical, stability ±5ppm/year Standard ±0.1% TCR = ±0.6ppm/° C typical, stability = ±5ppm/year Resistors 25, 100, 400 ±0.1% TCR = ±0.3ppm/°...

  • Page 96: Approvals

    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...

  • Page 97: Standards Applied

    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...

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