Temperature Controller - Fluke 7009 User Manual

General Operation
8.6

Temperature Controller

The bath temperature is controlled by Fluke Calibration's unique hybrid digi-
tal/analog temperature controller. The controller offers the tight control stability
of an analog temperature controller as well as the flexibility and programmabil-
ity of a digital controller.
The bath temperature is monitored with a platinum resistance sensor in the con-
trol probe. The signal is electronically compared with the programmable refer-
ence signal, amplified, and then fed to a pulse-width modulator circuit which
controls the amount of power applied to the bath heater.
The bath is operable within the temperature range given in the specifications.
For protection against solid-state relay failure or other circuit failure, the
microcontroller will automatically turn off the heater with a second mechanical
relay anytime the bath temperature is more than a certain amount above the
set-point temperature. As a second protection device, the controller is also
equipped with a separate thermocouple temperature monitoring circuit which
will shut off the heater if the temperature exceeds the cutout set-point.
The controller allows the operator to set the bath temperature with high resolu-
tion, set the cutout, adjust the proportional band, monitor the heater output
power, and program the controller configuration and calibration parameters.
The controller may be operated in temperature units of degrees Celsius or Fahr-
enheit. The controller is operated and programmed from the front control panel
using the four key switches and digital LED display. The controller may also be
optionally equipped with an serial RS-232 or IEEE-488 GPIB digital interface
for remote operation. Operation of the controller using the front control panel is
discussed following in Section. Operation using the digital interfaces is dis-
cussed in Section.
When the controller is set to a new set-point the bath will heat or cool to the
new temperature. Once the new temperature is reached the bath usually takes
10-15 minutes for the temperature to settle and stabilize. There may be a small
overshoot or undershoot of about 0.5°C.
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