Precision Blackbodies

Graphite Tube Blackbody Temperature Controller


  1. A 4 line by 20 character LCD display that simultaneously shows:
    • Black body temperature in C, F, or K with 0.1 resolution.
    • Set point temperature in C, F or K with 0.1 resolution.
    • Set point step size.
    • Output hold flag.

  2. Set point increments of 1, 10, and 100 C
  3. Set point is changed by either using the numerical keypad or by pressing the increment and decrement keys. Pressing the increment or decrement key will change the set point by the amount of the set point increment.
  4. A standard RS-232 port is provided to allow connection to a computer and can be used for:
    • Monitoring blackbody temperature
    • Changing set point.
Controller Model 7000A for Graphite Tube Blackbody

Controller Front Panel with Keypad
(NB: Model 7000 shown appears almost identical to Model 7000A)



The model HT-7000A is a high precision, three-term, Proportional, Integral, Derivative (PID) furnace controller specifically designed for the Thermo Gauge Brookley tube furnace. It uses as a control input, the cavity temperaturedital output from an automatic optical pyrometer. The combination of the HT-7000A controller and the Exactus pyrometer makes a highly repeatable, highly stable system that is used for precision high temperature work.

The controller operates stand-alone and is dedicated to maintaining the temperature of the blackbody. An RS-232 port is provided to allow the user to monitor the status and temperature of the blackbody and to change the temperature set point. The controller has a temperature resolution of 0.1 and controls the furnace temperature to ±0.1 C over most of the temperature range (±0.3 C at the extremes). The use of an alphanumeric display screen simplifies the operation of the furnace and assists the operator by a series of screen prompts.



  • The input to the HT-7000A is located on the rear panel of the controller. The input is a plug and is designed to connect to the pyrometer.

  • The output of the HT-7000A controller is located on the rear panel of the controller and is a shielded circular DIN Standard connector. This output connects to the furnace "EXTERNAL INPUT" and is the 0-5V-DC signal that controls the power level of the furnace.

  • There is one dual input/output port on the HT-7000A. It is located on the rear panel of the controller. It is a standard DB-9 connector and operates at RS-232 logic voltage levels. This port is used to interface to a computer for remote control of the furnace or for data recording.


    To change the set point, press the set point key, enter the new set point then press the key again.


    Setup is used to select three things

    1. STEP SIZE - selects the set point step size in the same units that are selected. When in the setup mode and 1 is pressed the step size changes to the next predefined value.

    2. UNITS - select the units for the system, F, C, K. When in the setup mode and 2 is pressed the units change to the next unit in the list.

    3. RAMP - selects the predefined ramp rate. When in the setup mode and 3 is pressed the ramp rate changes to the next value in the list.

           INC and DEC:

    The "INC" (increment) and "DEC" (decrement) keys are used to increase or decrease the set point. When the "INC" key is pressed the set point will increase by the selected step size. When the "DEC" key is pressed the set point will decrease by the selected step size.


    The "HOLD" key is used to hold the output of the controller at its present value. When "HOLD" is pressed the controller is disabled and the output is held at its present value. When "HOLD" is pressed a second time the controller will begin controlling at the present temperature. This is useful in special applications when the control loop must be interrupted.


    Following the appropriate procedures in the furnace operation manual align the Exactus optical pyrometer with the blackbody at the proper focal length. Connect the output of the Exactus to the HT-7000A. The system is now ready for operation.

    Turn on the HT-7000A. The default settings are set point = 800C and step size = 100.0C. 

    If the furnace power supply is on and all interlocks are clear the furnace will heat and stabilize at 800 C.

    After the system is stable at 800C the set point can be changed by pressing the "INC" or "DEC" keys or by entering a set point on the keypad. If the "INC" or DEC" keys are used, the set point will change by the step size. Step size is indicated in the LCD display.

    To shut down the system press the "Stand by" button on the furnace power supply. When the black body has stopped glowing and is dark black, turn off the purge gas. After the black body has been dark for 5 minutes, turn off the cooling water. Then turn off the HT-7000A.


    The HT-7000A can be interfaced to a computer that has a standard RS-232 port. The RS-232 port is configured as baud rate = 19600 bps, no parity, 1 start bit and 1 stop bits. The communication has no handshaking and uses a standard 1to1 DB-9 cable.

    The HT-7000A continuously sends ASCII string data out the RS-232 port; data sent is temperature in degrees C. The ASCII format is universal and easy to interpret.

    Copyright 2003 Thermo Gauge Instruments, Inc. , All rights reserved