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8.3.2
Setting Coefficients
Once an HTPRT probe is properly connected to the 2561, the 1560 can read 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 range for ITS-90 characterizations.
8.3.3
Current
The 2561 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 normal current is
3.0 mA. The current can be changed to 5.0 mA to test self-heating effects using
the SET UP DEVICE function in the MODULE menu (see Section 5.4.2).
Change the CURRENT parameter from 3.0 to 5.0 and press ENTER.
The SET UP DEVICE function also allows access to one other parameter.
SAMP PER selects the sample period between 2 (normal) and 10 seconds. The
purpose of this option is mainly for troubleshooting and it should not be
changed during normal operation.
8.3.4
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 2561 HTPRT Module. The device number of the HTPRT Input De-
vice is 1. The module number for the 2561 module is its position in the stack.
For example, if the 1560 has four add-on modules, the 2561 being first, the
module number for the 2561 is 1. Table 24 shows the device commands used to
read or set the setup parameters of the HTPRT Input Device.
Table 24 HTPRT Module Device Commands
Device Command
Below are some examples of using the device commands to set the device setup
parameters. For these examples it is assumed that the 2561 HTPRT Module is
placed first in the stack. These commands can be sent through any communica-
tion interface including the IEEE-488 and RS-232 interfaces.
SYST: MOD1:DEV1:WRIT "CURR",5 Set the excitation current to 5.0
mA.
SYST:MOD1:DEV1:READ? "CURR" Read the excitation current.
Parameter
CURR
3, 5
SAMP
2, 10
8 2561 HTPRT Module
Description
Excitation current, mA
Sample period, seconds
Operation
121
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