Fluke Hart Scientific 1575 Super-Thermometer User Manual page 149

Problem
Poor accuracy
Solution
The measurements do not seem to be as accurate as you expect.
Possible causes are the following:
•
The current may be too low. Check the current by dis-
playing its value in one of the programmable data fields
(see Section 7.5.3). (See the suggested current settings
for various types of sensors in Section 7.4.3.4)
•
The current may be too high leading to self-heating er-
ror. Check the current by displaying its value in one of
the programmable data fields (see Section 7.5.3). (See
the suggested current settings for various types of sen-
sors in Section 7.4.3.4.)
•
The reference resistor selection may be incorrect. Check
the reference by displaying its value in one of the pro-
grammable data fields (see Section 7.5.3). (See the sug-
gested reference selections for various types of sensors
in Section 7.4.3.3.)
•
The filter may not be set correctly (see Section 7.2.4).
Use the exponential or moving average filter with an ad-
equate time constant (20 to 60 seconds). Make sure the
filter threshold is greater than the normal variations in
the measurement (the message "FILTER RESET" will
be displayed if this is a problem).
•
The temperature conversion type or probe characteriza-
tion coefficients may be in error (see Section 7.4.3.2).
Check each of the probe parameters carefully. Make
sure the 3W OFFSET parameter is 0 unless you are us-
ing a three-wire or two-wire probe (see Section 7.4.3.5).
Make sure the correct probe setup is being used with the
measurements. Check the resistance-temperature con-
version calculations using the CONV TEST function and
compare with the calibration report table for your probe
(see Section 7.4.4.5).
•
Check to make sure the internal reference resistor cali-
bration values are correct (see Section 7.6.5.2). Com-
pare them with the 1575/1590 calibration report. Check
the calibration by checking the measured resistance of a
calibrated standard resistor.
•
Make sure the probe wires are properly and tightly con-
nected to the input patented DWF connectors.
•
Check the accuracy of your probe against measure-
ments of another probe or SPRT.
•
Room temperature variations or air drafts near the
1575/1590 can be a problem. Make sure the instrument
is operated in a stable environment. Also make sure
there are no strong electromagnetic interference near
the 1575/1590 or devices connected to it.
•
You may be expecting better accuracy than the specifi-
cations suggest. Review the specifications (Section 3.1)
and the discussion on evaluating uncertainty (Section
6.2.2).
13 Troubleshooting
Troubleshooting
139