Fluke 7341 User Manual page 76

Problem
The controller controls or at-
tempts to control at an inaccurate
temperature
The controller does not maintain
controller parameters or parame-
ters are reset each time the
power to the unit is removed
The controller shows that the out-
put power is steady but the pro-
cess temperature is unstable
The controller alternately heats
for a while then cools
Causes and Solutions
The controller operates normally except when controlling at a speci-
fied set-point. At this set-point, the temperature displayed does not
agree with the temperature measured by the user's reference ther-
mometer 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 tempera-
ture, by erroneous bath calibration parameters, or by a damaged con-
trol 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 ac-
cording to the Report of Test. If not, re-program the con-
stants. The memory backup battery may be weak
causing errors in data as described in the problem: 'The
display flashes "cutout" and an incorrect process tem-
perature'.
•
Check that the control probe has not been struck, bent,
or damaged. If the cause of the problem remains un-
known, contact an Authorized Service Center (see Sec-
tion 1.3, on page 5) for assistance.
Note: Before performing the memory check,you need to record the
controller calibration parameters (found in the CAL menu of the instru-
ment) 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 num-
ber such as 0002, the battery is spent and should be replaced. Con-
tact an Authorized Service Center for assistance.
5. After replacing the battery, you must reprogram the calibration and
user-adjustable parameters into the controller.
Possible causes are an improper proportional band setting or the fluid
being used.
•
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 Section 9.9, Proportional Band.
•
Check to ensure the fluid has not deteriorated or is not
too thick.
The bath 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 stabilizes as discussed in
Section 9.9, Proportional Band.
13 Troubleshooting
Troubleshooting
73