Troubleshooting - Fluke 7080 User Manual

Problem Causes and Solutions
The controller controls or If the controller appears to operate normally except that the bath's temperature
attempts to control at an does not agree with the temperature measured by the user's reference ther-
inaccurate temperature mometer to within the specified accuracy, consider the following:
Erroneous parameters. Check that the calibration parameters are all correct
according to the Report of Calibration. If not, reprogram the constants. If the
controller does not keep the correct parameters, the memory backup battery
may be weak causing errors in data. See "Low Battery" in a previous solution.
Poor uniformity. There may be an actual difference between the bath's control
probe and the reference thermometer due to excess gradients in the bath.
Check that the bath has an adequate amount of fluid in the tank and that the
stirrer is operating properly. Also check that the reference thermometer and
control probe are both fully inserted into the bath to minimize temperature gradi-
ent errors.
Bad control probe. Check that the control probe has not been struck, bent, or
damaged. Refer to the previous solution for how to check the probe's
resistance.
The controller shows that If the bath does not achieve the expected degree of temperature stability when
it is controlling at the measured using a thermometer, consider the following:
proper temperature, but
the bath temperature is
Wrong proportional band setting. If the proportional band is set too narrow,
unstable
the bath will oscillate causing poor stability. In this case, increase the width of
the proportional band.
If the proportional band setting is too wide, the long-term stability of the bath is
affected. In this case decrease the width of the band. (Refer to section 9.7.)
Bath fluid is too thick. Make sure that the bath fluid used is less than 50 centi-
Stokes (10 is ideal) at the temperature at which the bath is controlling. Check
the fluid manufacturer's specifications.
You should also change the bath fluid regularly and if it changes colors or be-
comes too thick.
Bad control probe. Check that the control probe has not been struck, bent, or
damaged. Refer to the previous solution for how to check the probe's
resistance.
The controller alternately
Wrong proportional band setting. If the proportional band is set too narrow,
heats for a while then the bath will oscillate between too much heating and too much cooling causing
cools instability. Increase the width of the proportional band until the temperature sta-
bilizes. (Refer to section 9.7.)

13 Troubleshooting

Troubleshooting
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