Fluke Hart Scientific 1575 Super-Thermometer User Manual page 148

1575/1590 Thermometer Readout
User's Guide
138
Problem
Excessive variation from one
measurement to the next
Solution
The variation from one measurement to the next (noise) appears to be
greater than normal. Possible causes of this 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 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).
•
You might be experiencing electromagnetic interference
(EMI). Make sure there are no strong sources of electro-
magnetic interference near the 1575/1590 or other de-
vices connected to it. Use a probe that has shielded
cable and attach the guard wire of the cable to the
'Guard' patented DWF connector, the 'Chassis' patented
DWF connector, or both (see Section 4.5). Try attaching
a ground wire between the 'Chassis' patented DWF con-
nector on the 1575/1590 and the chassis of the tempera-
ture source. If the probe has no shield or guard try
simply connecting a wire between the 'Guard' and
'Chassis' patented DWF connectors.
•
Room temperature variations or air drafts near the
1575/1590 can be a problem. Make sure the instrument
is operated in a stable environment.