Fluke 6050H User Manual page 65

Problem
The controller controls or attempts to
control at an inaccurate temperature
The controller shows that it is controlling at
the proper temperature, but the bath
temperature is unstable
The controller alternately heats for a while
then cools
Stir motor does not function
Causes and Solutions
If the controller appears to operate normally except
that the bath's temperature does not agree with the
temperature measured by the user's reference
thermometer 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 gradient errors.
Defective 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.
If the bath does not achieve the expected degree of
temperature stability when measured using a
thermometer, consider the following:
Wrong proportional band setting. If the proportional
band is set too narrow, 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.
Bath salt is too thick. Make sure that the bath salt
used is less than 50 centistokes (10 is ideal) at the
temperature at which the bath is controlling. Check
the salt manufacturer's specifications.
Defective 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.
Wrong proportional band setting. If the proportional
band is set too narrow, the bath will oscillate between
too much heating and too much cooling causing
instability. Increase the width of the proportional band
until the temperature stabilizes.
Improper setting or normal operation. See Section
9.11.2, Stir Mode Select, for proper stir mode settings.
Calibration Bath
Troubleshooting
57