Oxford Instrucments ITC503 Operator's Handbook Manual
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Oxford Instrucments ITC503 Operator's Handbook Manual

Temperature controller
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See also: Operator's Handbook Manual
Operator's Handbook
ITC503
Temperature controller
Issue 4
April 2000
File reference: ITC503-4.DOC
Oxford Instruments
Superconductivity
Tubney Woods, Abingdon,
Oxon, OX13 5QX, England
Tel: +44 (0)1865 393 200
Fax: +44 (0)1865 393 333
E-mail:superconductivity@oxinst.co.uk
www.oxford-instruments.com

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  • Page 1 Operator’s Handbook ITC503 Temperature controller Issue 4 April 2000 File reference: ITC503-4.DOC Oxford Instruments Superconductivity Tubney Woods, Abingdon, Oxon, OX13 5QX, England Tel: +44 (0)1865 393 200 Fax: +44 (0)1865 393 333 E-mail:superconductivity@oxinst.co.uk www.oxford-instruments.com...

  • Page 2: Table Of Contents

    Protective Ground ..................5 Repair and Adjustment ................5 Introduction ......................6 Use of this Manual..................6 Description of ITC503 ................. 6 Installation ........................ 8 Supply Connections ..................8 Heater and Sensor Connections..............8 RS232 Serial Data Line Connections ............9 The Oxford Instruments ISOBUS ..............
  • Page 3 Monitoring the Progress of a Sweep............28 Stopping a Sweep..................29 Programming the Sweep ................. 29 Storing a Sweep Program ................ 30 Calibration and Configuration................31 Sensor Calibration ..................31 Storing the Calibration................32 Gas Flow and Cryocooler................32 7.3.1 Adjusting the Valve Gearing..........
  • Page 4 15.1 Circuit Description ..................64 15.2 Test Mode ....................66 In Case of Difficulty ....................67 Differences Between ITC503 and ITC4..............70 Specification......................72 Appendix 1 - Capacitance Sensor Input..............74 19.1 Description of Capacitance Sensor Input Board ........74 19.1.1...

  • Page 5: Safety

    1 Safety The following general safety precautions must be observed during the operation, service and repair of this instrument. Protective Ground To minimise shock hazard the instrument must be connected to an electrical ground. The ground wire (green/yellow) in the instrument power cable must be connected to the installation electrical ground system.

  • Page 6: Introduction

    (EPROM). This program is referred to as the ITC503 firmware. The firmware is coded with a two part number (for example 1.01) where the first digit indicates a major version of the firmware and the second two digits cover minor revisions.
  • Page 7 ITC503 offers automatic selection of appropriate control parameters (PID values) for operation throughout its working range. These parameters may themselves be "learnt" for a particular system, by use of ITC503 operating in conjunction with the Oxford Instruments Object-Bench software, supplied with the instrument.

  • Page 8: Installation

    3 Installation Supply Connections Before applying power to the instrument, ensure that the voltage selector on the rear panel is correctly set for the intended supply voltage. If necessary, open the voltage selector panel using the slot provided, withdraw the voltage selector and replace it in the correct orientation for the intended voltage.

  • Page 9: Rs232 Serial Data Line Connections

    The bi-directional serial data link from the computer is connected via a 25 way D-socket on the rear panel. ITC503 is configured as a DCE with the standard pin outs given below. The majority of computer RS232 interfaces are configured as a DTE and are fitted with a 25 way D plug.

  • Page 10: The Oxford Instruments Isobus

    None The Oxford Instruments ISOBUS A unique feature of ITC503 and other Oxford Instruments products, is the ability to connect a number of instruments simultaneously, to a single RS232 port on a computer and to control each one independently. This is done by means of an ISOBUS cable which carries a single MASTER connector (25-way D socket) and up to eight, daisy-chained SLAVE connectors (25-way D plugs).

  • Page 11: The Gpib To Isobus Gateway

    Before any communication can occur, ITC503 must be given a unique GPIB address. By default, ITC503 is supplied with its address set to 24. If this address is already in use by another instrument on the bus, it can be changed from the front panel via the Test Mode.
  • Page 12 b) It provides an over-ride input to disable the heater output. This is intended for use with a separate over -temperature cut-out switch and displays the message "Hot 0". c) It provides a pseudo-analogue temperature output for use with a chart recorder. (Should be used in conjunction with the Oxford Instruments Chart Recorder output lead, which incorporates the necessary pull-up resistor and passive filter).

  • Page 13: Analogue Output

    A second similar output on pin 4 monitors the current position of the gas control valve. This allows for the use of a variable speed cryohead motor, controlled by the analogue voltage when ITC503 is used in conjunction with a cryocooler. ITC heater control board The standard ITC, with or without the extra sensor channel interface board (SCI), has a single heater output.

  • Page 14: Room Temperature Thermocouple

    The ITC503 RT sensor is normally set to provide a 39 µV/degree compensation, which is correct for Chromel/Alumel and Copper/Constantan thermocouples. Other values of compensation may be obtained by changing the value of R156 on the input PCB.

  • Page 15: Use Of Rt Reference With Channels 2 & 3

    Use of RT Reference with Channels 2 & 3 ITC503 does not have a separate RT sensor for channels 2 & 3 (where fitted). Where RT compensation is required on only one channel of a multi channel instrument, Channel 1 should be employed for this purpose.

  • Page 16: Local Operation

    "knowing" if there is a computer connected to the RS232 interface. When ITC503 is in REMOTE, many of the front panel controls are disabled. Those controls which only affect the display, will still work but those which could change the operation of the instrument will not.
  • Page 17 PID if no learnt data has been loaded. HEATER The normal way in which ITC503 effects its control, is by applying power to a heater. In MANUAL control the heater voltage may be varied by RAISE and LOWER. In AUTOMATIC control the heater voltage is varied in response to the difference between a measured temperature and a set-point.
  • Page 18 In this application if GAS FLOW is set to MANUAL, at a setting of zero, the cryocooler compressor is automatically shut down. SWEEP The ITC503 incorporates a programmable sweep facility. This is controlled by a single RUN/PROGRAM button with three lamps. It is described in detail in section 6. DISPLAY The main display normally indicates the measured temperature.

  • Page 19: First Time Operation

    This button is disabled unless ITC503 is in LOCAL and the heater is set to MANUAL. When changing control sensors ITC503 will automatically reset the SET temperature as described in section 4.1 under HEATER.

  • Page 20: Automatic Heater Control

    RAISE and LOWER may be used to vary the control terms whilst in LOCAL control. Once a set of values has been chosen, they may be retained in the ITC503's non-volatile memory and will not need resetting at switch on, provided a STORE operation is performed (section 5.6).
  • Page 21 This can cause some confusion when the concept of PID control is first encountered. Unlike the ITC502 there is no facility for associating PID values with each step. On the ITC503 this is acheived more simply by use of the Auto PID feature, as decribed in the following section.

  • Page 22: Automatic Setting Of P, I & D Control Terms

    5 (See section 7.4). Gas Flow Control ITC503 is able to control a motorised needle valve, regulating the flow of cryogen used to cool a sample. The needle valve may either be fitted to the main cryostat, controlling the...

  • Page 23: Cryocooler Control

    Although not normally necessary, it is possible to separately tune the gas flow control. This is described below in section 7.3. When automatic gas control is used on its own, ITC503 attempts to control at the desired set temperature in the usual way. When automatic gas flow is used in conjunction with...
  • Page 24 Test mode is entered from the front panel by holding the two red buttons RAISE and LOWER pressed, whilst pressing and releasing the LOC/REM button. ITC503 will display the message: tESt to indicate that it is entering test mode. After a second this will change to;...

  • Page 25: Limits

    Warning: An ITC503 which has not been supplied as part of a complete system, will normally be shipped with the limits disabled in this way. If your cryostat can be damaged by over-temperature, you should set appropriate limits before operating the system.

  • Page 26: Limiting Set Temperature

    If after 10 seconds the temperature is still above the limit, ITC503 will assume that a fault may have occurred in the heater circuit. It will therefore open its output safety relay, completely isolating the heater from the controller output.

  • Page 27: Storing Limits And Other Power-Up Defaults

    or something similar. RAISE and LOWER may be used to move the position of the decimal point within this display, which indicates how many decimal places will be be displayed at the lowest temperature. In the example shown the display will give 3 decimal places, and hence 0.001K resolution.

  • Page 28: Sweep

    Remember that the sweep facility programs the ITC503 set point. The measured temperature will tend to lag behind the set point by an amount dependant upon the response time of the system. Remember also that ITC503 must be set to AUTO if the actual temperature is to be varied!

  • Page 29: Stopping A Sweep

    A Sweep Program may be entered from the front panel, starting with the controller in LOCAL. The method is as follows: Press RUN/PROGRAM and hold it in. Wait till the display changes from "run" to "Pro", then release the button. ITC503 is now in the program mode and the display will indicate P 01 showing that the first program step is to be examined.

  • Page 30: Storing A Sweep Program

    Where a program of less than the full 16 steps is required, the SWEEP and HOLD times for all the unused steps should be set to zero. When the program is run, ITC503 will automatically bypass these steps. The programmed temperature of step "P 16" has a special significance.

  • Page 31: Calibration And Configuration

    7 Calibration and Configuration Sensor Calibration To match ITC503 to the exact characteristics of a specific sensor, a calibration must be carried out at the two ends of the working range. This is achieved by means of the recessed CAL button.

  • Page 32: Storing The Calibration

    Storing the Calibration Normally after a change has been made to the calibration, it is desirable that the new calibration is retained when the instrument is switched off. Thus the calibration data must be stored, using the LIMIT and LOC/REM buttons as described in section 5.6. Gas Flow and Cryocooler Configuration Before the Gas Flow control algorithm can be used, it must be configured for a particular combination of hardware.

  • Page 33: Adjusting The Valve Gearing

    The table below shows the full list and these are described in detail in the following sections. Exit (Resumes normal operation) Valve Gearing Target Table & Features Configuration Gas Flow Scaling Temperature Error Sensitivity Heater Voltage Error Sensitivity Minimum Gas Valve in Auto (Unused) 7.3.1 Adjusting the Valve Gearing...

  • Page 34: Adjusting The Error Sensitivities

    The minimum valve position is displayed as a percentage and may be adjusted in the range 0.0% to 99.9%. The default value is 0% for a stand alone ITC503. Where the ITC503 has been supplied as part of a complete system, this parameter will have been set to an optimum value during system testing at the factory.

  • Page 35: Remote Operation

    ITC503 will accept a command string at all times. If a computer linked by the serial (RS232) port, is unable to accept data from ITC503 at the full rate of the 9600 baud interface, the "W" command may be used to instruct ITC503 to send more slowly.

  • Page 36: Numeric Parameters

    "?" will always be the first character returned. The most common reason for a command error is attempting to execute a control command whilst ITC503 is in LOCAL control. If in doubt, the "X" command may be used to determine the current status.

  • Page 37: The Gpib Interface

    & (Ampersand) instructs an instrument to ignore any following ISOBUS control characters. It is included in the ISOBUS protocol to allow instruments whose command repertoire includes "@", "$", "&" or "!" to be used on ISOBUS. ITC503 does not require the use of this command.

  • Page 38: Sending Commands Via The Gpib

    This is fine until something unexpected happens. A better alternative is to read a STATUS BYTE from the instrument by conducting a SERIAL POLL of it. The ITC503 interface will always respond to a serial poll and will return a status byte. Three bits in this byte have significance for ITC503 as follows.

  • Page 39: Use Of The Service Request Line

    ITC503 updates the status byte every millisecond. Thus if the Status Byte is read within 1mS of reading data from the interface, The MAV and BAV bits may not yet have been cleared, even though all available data has been read. If these bits are found to be unexpectedly set immediately after a data read, a second read of the Status byte at least 1mS later will confirm whether there really is data remaining.

  • Page 40: Compatibility With Ieee-488.2

    8.6.8 Compatibility with IEEE-488.2 Compatibility with certain aspects of this extension to the original standard has already been mentioned in a number of places (for example the format of the Status Byte). However details of the command sequences and formats within messages, error handling and status reporting all follow the existing ITC syntax and protocols used on RS232.

  • Page 41: Command List

    They provide a means to preload certain advanced control features associated with the GAS FLOW algorithm and to read diagnostic information from the ITC503 to assist with control algorithm development. In the list which follows, "n" represents a decimal digit 0-9.
  • Page 42 SYSTEM COMMANDS (recognised only after correct Unnnnn command) LOAD ENTIRE RAM CONTENTS DUMP ENTIRE RAM CONTENTS STORE RAM CONTENT TO EEPROM SET ISOBUS ADDRESS (See section 8.5) SPECIALIST COMMANDS (all lower-case letters) xnnn SET TABLE POINTER x to nnn ynnn SET TABLE POINTER y to nnn snnnnn PROGRAM SWEEP TABLE...

  • Page 43: Command Syntax

    User Commands Cn COMMAND The control command sets ITC503 into LOCAL or REMOTE and determines whether the LOC/REM button is LOCKED or active. At power up ITC503 defaults to the C0 state. Allowed values are: LOCAL & LOCKED (Default State) REMOTE &...
  • Page 44 Wnnnn COMMAND The WAIT command sets a delay interval before each character is sent from ITC503 via the computer interface. This allows ITC503 to communicate with a slow computer with no input buffering. The parameter nnnn specifies the delay in milliseconds. It defaults to zero...
  • Page 45 (N.B. the W command does not reduce the rate at which ITC503 can accept data from computer.) X COMMAND The EXAMINE command allows the computer to read the current ITC503 STATUS. It requires no parameters and will return a message string of the form: XnAnCnSnnHnLn where the digits "n"...
  • Page 46 "L1" command will not be available and will produce a "?L1" error response. Mnnn COMMAND The MAXIMUM HEATER command sets the maximum heater voltage that ITC503 may deliver, under automatic control or in response to an "O" command. This performs the same function as the Output Limit described in section 5.1.

  • Page 47: Specialist Commands

    Tnnnnn COMMAND The TEMPERATURE command sets a set point temperature. The parameter is the required temperature, sent as an signed decimal number in accordance with section 8.4. Note that if a sweep is running, the temperature set by the T command will be over- ridden by the sweep.
  • Page 48 Sweep Time to Set Point Hold Time at Set Point To program a sweep, ITC503 must be in REMOTE and a sweep must not be running. r COMMAND (Read Sweep Table) The r command allows the individual steps of the sweep table to be read back, using the x and y pointers as above.
  • Page 49 q COMMAND (Read Auto-PID Table) The q command allows the individual entries in the Auto-PID table to be read back, using the x and y pointers as above. vnnn COMMAND (Program Custom Target Heater Voltage Table) Programs values into the custom target heater voltage table, which may be used for automatic Gas Flow Control.

  • Page 50: Sensor Range Configuration

    11.1 Introduction Each sensor input channel of ITC503 may be configured to a range suitable for use with a specific sensor. Normally an instrument is supplied with the specified range(s) configured ready for use. However it is possible to reconfigure it for use with different sensors should this be required.

  • Page 51: Range Data

    11.2 Range Data CODE SENSOR RANGE Tref (Rear Switch) (Front Switch Linear Range 0-1677.7 (As required, See Note 2) Null Centre Zero -838.9- +838.9 (As required, See Note 2) Con 1 Conductance 0-20 00001 11110 01001 01010 TG 5 AuFe 0.03/Chr 2-500K 4.2K 11000 11111...

  • Page 52: Access To Configuration Controls

    11.3 Access to Configuration Controls Configuring ITC503 involves setting switches on the input board and selecting the appropriate linearisation data table. To carry out this work the top cover of the instrument must be removed. Before attempting this, read the Safety Information in Section 1 of this manual.

  • Page 53: Linearisation Configuration

    SW1 is split into two sections each of 5 switches. SW1/1 to SW1/5 define the input span, whilst SW1/6 to SW1/10 define the input zero. The pattern on the switches may be regarded as a binary number with the highest numbered switch being the least significant bit.
  • Page 54 Press LOC/REM and the range will be configured. ITC503 will then leave the test mode and start normal operation with the "PASS" message. After re-configuring a range, it will be necessary to carry out the calibration described in section 7.

  • Page 55: Sensor Range Design

    12.1 Introduction The preceding section described how to configure ITC503 to use a range already installed in either the program or non-volatile memories. This section describes how a range may be designed and loaded into one of the non-volatile memory tables. It is not practicable to design and load an ITC503 range "by hand".

  • Page 56: Selecting Input Configuration

    12.3 Selecting Input Configuration Having decided upon the sensor type the input stage configuration may be determined and the settings for SW2/4 to SW2/9 established. The details which follow are for reference only. The Object Bench Custom Range utility will automatically indicate the correct settings.

  • Page 57: Selecting Zero And Span

    Data No details of the linearisation calculation process are provided here. To achieve the required accuracy needed for auto ranging at low temperatures, ITC503 employs a more complicated linearisation algorithm than ITC502 with a totally different data structure. The calculations and data transfer should only be attempted with the aid of Object Bench...

  • Page 58: Theory Of Calibration And Linearisation

    13 Theory of Calibration and Linearisation In the interests of long term stability and ease of adjustment, ITC503 contains no conventional calibration presets. Instead the calibration constants are held in the non- volatile memory and "adjusted" to match a particular sensor by means of the front panel controls.

  • Page 59: Theory Of Control

    The hot plates on a domestic cooker are an example of this form of "control". This mode of operation can be obtained with ITC503 in its MANUAL mode. 14.3 On-Off Control In an on-off (or "bang-bang") control system the heater power is either full on (if the...

  • Page 60: Integral Action

    The range over which the output is proportional to the input is the PROPORTIONAL BAND. In ITC503 this is expressed directly in degrees. By reducing the proportional band, the accuracy of the controller may be improved since a smaller error will then be necessary to produce a given change in output.

  • Page 61: Derivative Action

    14.8 Theory of Gas Flow Control ITC503 has the ability to drive a motorised needle valve. In the GAS AUTO mode the position of the needle valve is controlled automatically to provide variable cooling power in conjunction with the heater for temperature control.
  • Page 62 This allows the ITC503 to be matched to a variety of different needle valve and stepper motor combinations. Total numbers of steps between 512 and 65536 can be accommodated, in binary increments.
  • Page 63 A next level would be to ensure that the target voltage is sufficient to ensure that the heater voltage never falls to zero when correcting for minor fluctuations during steady state control. This can give good control stability at the sensor and heat exchanger and is a good operating strategy for so called "static"...

  • Page 64: Servicing

    PCB to monitor mains volts. Should this fall below 8 volts, a RESET is performed. (If ITC503 is operated on very low mains volts, it may keep resetting. This may be identified by the "PASS" message reappearing during use.) The main transformer also generates an 18v AC supply for the input circuits.
  • Page 65 The microprocessor circuit is conventional and incorporates CPU, EPROM, RAM, CTC and UART chips. The keyboard and display are mapped directly as i/o ports on the microprocessor bus and the CPU handles all the display decoding and multiplexing in software. An EEPROM U3, is used to retain data when the instrument is powered down.

  • Page 66: Test Mode

    15.2 Test Mode ITC503 performs a basic self test of the microprocessor and memory at switch on, before displaying the "PASS" message. A more detailed hardware test mode is available for help during fault finding. This has already been described in section 4.12. In that section entering test mode from the front panel was described.

  • Page 67: In Case Of Difficulty

    Controller is set to REMOTE HEATER SENSOR appears not to change sensor Controller is in REMOTE or AUTO ITC503 appears to control with a large offset INT time has been set to a very large value. ITC503 only moves very slowly towards set point...
  • Page 68 SWEEP RUN/PROG pressed. HEATER SENSOR changed (see section 4.3). "PASS" message appears during operation Low mains voltage. ITC503 is resetting. It will switch to MAN with output at zero. Check mains voltage setting is correct. Calibration changes when RAISE/LOWER pressed CAL button stuck in.
  • Page 69 If switching the power off and on does not cure the problem, or if it was initially discovered at switch on, the contents of the EEPROM itself may be corrupt. There are two reset procedures which may assist in diagnosing the problem. A two-button reset is carried out by holding the RAISE button pressed, whilst pressing and releasing the internal RED test button S1 on the main PCB (See section 11).

  • Page 70: Differences Between Itc503 And Itc4

    Auto PID Operation ITC503 can select PID values automatically based on its set temperature. The data used can be learned automatically for a particular system by running ITC503 in conjunction with Object Bench software.
  • Page 71 GATEWAY facility allows this to act as an adaptor to older instruments such as ITC4 via ISOBUS. Self Test Display As part of self test, ITC503 displays its GPIB address or its ISOBUS address, before the "PASS" message. Improved Input Filtering Additional filtering has been added to the input and current source connections.

  • Page 72: Specification

    18 Specification INPUT CHANNELS 1 standard, 3 optional INPUT RANGE 5mV TO 2V FSD INPUT OFFSET -2v to +2v CURRENT SOURCE 10uA, 100uA, 1mA (+/-10%) SENSOR TYPES Voltage Input 5mV to 2V FSD Resistance Input 4-wire, 5 Ohm to 200 K Ohm FSD Thermocouple See List.
  • Page 73 CASE STYLE Freestanding Metal Case Optional Rack Mount Ears DIMENSIONS FREESTANDING 446mm x 106mm x 298mm RACK MOUNT 19 inch x 2U x 298mm WEIGHT 6.5kg...

  • Page 74: Appendix 1 - Capacitance Sensor Input

    The card is installed in the Channel 1 position in ITC503, leaving Channels 2 and 3 free for the primary sensor and an optional third sensor. When switching control from the primary sensor to the capacitance sensor,...

  • Page 75: Installation

    19.1.3 Installation The Capacitance Sensor Range Card is installed in ITC503 in place of the existing Channel 1 Range Card. Before attempting to install the card, ensure that the Safety Information given in the Section 1 has been read and that the instrument is completely disconnected from the supply mains.

  • Page 76: Connections

    The shield of the excitation lead should be left isolated at the cryostat end. Both shields are grounded at the ITC503 end. Within the cryostat, the two conductors are taken to the two ends of the sensor, using thin copper wire with good heatsinking to the point of measurement.

  • Page 77: Use Of The Capacitance Sensor Card

    (Note that this set point transfer will be carried out to the full precision of the ITC503, which may be greater than the displayed precision for the capacitance sensor). If desired, control stability may be verified by continuing to display the temperature from the primary sensor whilst controlling with the capacitance sensor.

  • Page 78: Circuit Description

    U6 to be converted to a frequency in the range 0 to 60kHz which is fed via the opto-isolator U7 to the ITC503 main PCB. High stability power rails are provided by U8 which derives its reference from diode D6.
  • Page 79 A capacitance sensor itself requires no room temperature reference compensation. Moreover since the sensor is for use in cryogenic systems it is not expected that any thermocouple sensors used for channels 2 and 3 will require a room temperature reference junction. However against the remote possibility that one should be required, provision is made on the board for the RT sensing circuit U9, R45.

  • Page 80: Circuit Diagrams

    20 Circuit Diagrams The following circuit diagrams are included, covering ITC503 itself, together with its accessories: Drawing Number No. of pages Description CQA1102 (1 sheet) POWER SUPPLY CQB0102 (1 sheet) KEY / DISPLAY BOARD CQB0202 (4 sheets) CPU / DIGITAL CONTROL BOARD...

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