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Problem
Causes and Solutions
The controller shows that
it is controlling at the
proper temperature, but
the bath temperature is
unstable
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. (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
heats for a while then
cools
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 sta-
bilizes. (Refer to section 9.7.)
The controller does not
maintain controller pa-
rameters or parameters
are reset each time the
power to the unit is
removed
Note:
Before performing the memory check, you need to record the controller
calibration parameters (found in the CAL menu of the instrument) and any
user-adjusted parameters that you have changed (such as the programmable
set points and proportional band).
Memory Check
Doing a memory check is the easiest way to verify the ability of the battery to
maintain controller parameters.
1. Power off the instrument.
2. Disconnect the instrument from AC power for 10 seconds.
3. Reconnect the AC power and power on the instrument.
4. If the display shows "InIT" and/or the cycle count shows a low number such
as 0002, the battery is spent and should be replaced. Contact an Authorized
Service Center for assistance.
5. After replacing the battery, you must reprogram the calibration and user-ad-
justable parameters into the controller.
Power Up
The instrument is equipped with operator accessible fuses. If a fuse blows, it
may be due to a power surge or failure of a component. Replace the fuse once.
Always replace the fuse with one of the same rating, voltage, and type. Never
replace the fuse with one of a higher current rating. If the fuse blows a second
time, it is likely caused by failure of a component part. If this occurs, contact an
Authorized Hart Scientific Service Center.
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13 Troubleshooting
Troubleshooting