Troubleshooting - Fluke 9116A User Manual

Problem
The controller controls or
attempts to control at an
inaccurate temperature
The controller shows that
the output power is steady,
but the process tempera-
ture is unstable
The controller alternately
heats for a while then
cools
The controller erratically
heats then cools, control is
unstable
The controller does not
maintain controller pa-
rameters or parame-
ters are reset each
time the power to the
unit is removed
Causes and Solutions
The controller operates normally except when controlling at a specified
set-point. At this set-point, the temperature displayed does not agree with
the temperature measured by the user's reference thermometer to within
the specified accuracy. This problem may be caused by an actual differ-
ence in temperature between the points where the control probe and ther-
mometer probe measure temperature, by erroneous instrument calibration
parameters, or by a damaged control probe.
Check that the thermometer probe and control probe are both fully in-
serted into the instrument to minimize temperature gradient errors.
Check that the calibration parameters are all correct according to the Re-
port of Test. If not, re-program the constants.
Check that the control probe has not been struck, bent, or damaged.
The instrument may be out of calibration, therefore it may be necessary to
perform the calibration procedure explained in the calibration section of
this manual.
Possible cause is an improper proportional band setting.
If the instrument temperature does not achieve the expected degree of
stability when measured using a thermometer, try adjusting the propor-
tional band to a narrower width as discussed in Section 6.8, Proportional
Band.
The instrument is not stable and the duty cycle is not constant.
The proportional band being too narrow typically causes this oscillation.
Increase the width of the proportional band until the temperature stabi-
lizes as discussed in Section 6.8, Proportional Band.
If both the instrument temperature and output power do not vary periodi-
cally but in a very erratic manner, the problem may be excess noise in the
system. Noise due to the control sensor should be very small. However, if
the probe has been damaged or has developed an intermittent short or
open, erratic behavior may exist.
Check for a damaged probe or poor connection between the probe and
controller.
Intermittent shorts in the heater or controller electronic circuitry may also
be a possible cause. Contact an Authorized Service Center (see Section
1.4, on page 5) for assistance.
Note: Before performing the memory check, you need to record the con-
troller 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 bat-
tery 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-adjustable parameters into the controller.

12 Troubleshooting

Troubleshooting
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