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10.3.2
Setting Coefficients
Once a thermistor is properly connected to the 2563, the 1560 can read out its
resistance. To display temperature accurately, the 1560 must be programmed
with the characterization coefficients for the sensor. This is done using the
EDIT PROBE soft-key in the PROBE menu (see Section 5.2.1). The coeffi-
cient values are normally provided with the probe on a calibration report. Be
sure to select the proper equation type, R(T) or T(R).
10.3.3
Current
The 2563 sources current to the sensor and measures the resulting voltage
across the sensor to determine its resistance. The current alternates every 0.5
seconds to reduce the effects of thermoelectric offsets. The current automati-
cally switches between 2 μA and 10 μA depending on the resistance being
measured. At lower resistances (below about 50 kΩ) 10 μA is used. At higher
resistances 2 μA is used. You can force the current source to use 2 μA for low
resistances, if necessary, using the SET UP DEVICE function in the MOD-
ULE menu (see Section5.4.2). Change the CURRENT parameter from AUTO
to 2.0 and press ENTER.
The SET UP DEVICE function also allows access to two other parameters.
SAMP PER selects the sample period between 2 (normal) and 10 seconds. RES
RANGE sets the resistance range between AUTO ranging (normal), LOW
range, and HIGH range. The purpose of these options is mainly for trouble-
shooting and they should not need to be changed during normal operation.
10.3.4
Device Setup Commands
The SYST:MODn:DEVn:READ? and SYST: MODn:DEVn:WRIT commands
(see Sections 6.5.8.19 and 6.5.8.20) can be used to read or set the setup param-
eters for the 2563 Thermistor Module. The device number of the Thermistor In-
put Device is 1. The module number for the 2563 module is its position in the
stack. For example, if the 1560 has four add-on modules, the 2563 being third,
the module number for the 2563 is 3. Table 26 shows the device commands
used to read or set the setup parameters of the Thermistor Input Device.
Below are some examples of using the device commands to set the device setup
parameters. For these examples it is assumed that the 2563 Thermistor Input
Table 26 Thermistor Module Device Commands
Device Command
Parameter
CURR
AUTO, 2, 10
SAMP
2, 10
ARNG
AUTO, LOW, HIGH
10 2563 Thermistor Module
Description
Excitation current, μA
Sample period, seconds
Resistance range
Operation
135
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