Fluke 7037 User Manual page 67

Problem
The controller controls or attempts to
control at an inaccurate temperature
The controller shows that the output power
is steady but the process temperature is
unstable
The controller alternately heats for a while
then cools
The controller erratically heats then cools,
control is unstable
Causes and Solutions
The controller operates normally except when con-
trolling at a specified set-point. At this set-point, the
temperature does not agree with that measured by the
user's reference thermometer to within the specified
accuracy. This problem may be caused by an actual
difference in temperature between the points where
the control probe and thermometer probe measure
temperature, by erroneous bath calibration
parameters, or by a damaged control probe.
Check that the bath has an adequate amount of fluid
in the tank and that the stirrer is operating properly.
Check that the thermometer probe and control probe
are both fully inserted into the bath to minimize
temperature gradient errors.
Check that the calibration parameters are all correct
according to the certification sheet. If not, reprogram
the constants. The memory backup battery may be
weak causing errors in data as described in the
problem 'The display flashes "cutout" and an incorrect
process temperature'.
Check that the control probe has not been struck,
bent, or damaged. If the cause of the problem remains
unknown, contact an Authorized Service Center for
assistance.
If the bath temperature does not achieve the expected
degree of stability when measured using a
thermometer, try adjusting the proportional band to a
narrower width as discussed in the Proportional Band
section.
This oscillation is typically caused by the proportional
band being too narrow. Increase the width of the
proportional band until the temperature stabilizes as
discussed in the Proportional Band section.
If both the bath temperature and output power do not
vary periodically but in a very erratic manner, the
problem may be excess noise in the system. Noise
due to the control sensor should be less than
0.001 °C. However, if the probe has been damaged or
has developed an intermittent short, erratic behavior
may exist. Check for a damaged probe or poor
connection between the probe and bath.
Intermittent shorts in the heater or controller electronic
Circuitry may also be a possible cause. Contact an
Authorized Service Center for assistance.
Calibration Bath
Troubleshooting
57