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The next screen sets the parameters relating to the measurement sequence. The
user can specify whether the temperature is to be measured only once (ONCE)
at the beginning for each calibration point or measured just prior to every resis-
tance measurement (REPEAT). Repeating the temperature measurement for
each probe may give better accuracy if the temperature is drifting.
You can select the measurement mode as TIMED or PROMPT. The TIMED
mode is useful when calibrating multiple probes simultaneously using the 2575
or 2590 Scanner. If TIMED is selected then the user must specify the DELAY
time in minutes between measurements. After switching to the next probe, the
1575/1590 will measure for this amount of time before automatically recording
the reading. The delay time should be at least five times the digital filter time
constant to allow enough time for transients to settle. With the PROMPT mode,
the thermometer will wait for you to press the STOP and STORE soft-keys to
record the next measurement. After setting these parameters, press the NEXT
soft-key (or Exit) to continue.
The last setup screen is used to set up SPRT resistance comparison calibrations.
This screen only appears if a reference SPRT was specified in the first screen
and its channel was set to INPUT 2. You specify whether to use the normal ref-
erence resistor (determined by REFERENCE in EDIT PROBE) or the SPRT
connected to Input 2 when measuring the resistances of the calibration probes.
Select NORM if the resistances are to be measured in ratio to the normal refer-
ence resistor (e.g. 100( internal resistor). Select SPRT if you desire to measure
the resistances in direct ratio with the SPRT. This mode may help improve the
accuracy when the temperature of the bath is drifting. If a fixed point is used
for a calibration point, such as the triple point of water, the resistance measure-
ments for that point will use the normal reference resistor rather than the SPRT.
After setting this parameter press the RETURN soft-key (or Exit) to go back to
the ITS-90 calibration menu. You are now ready to begin measuring using the
MEASURE function.
7.4.4.2.7
Measure
The MEASURE function is used to collect the temperature and resistance mea-
surements for the calibration. This requires that the setup step be performed
previously. The measurement process involves measuring the temperature and
then the probe resistances at each of the calibration points. You may measure
the calibration points in any order. The calibration point selection screen lists
the points required for the subranges you selected and allows you to select
1575/1590 Thermometer Readout
User’s Guide
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