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Advanced Programming with the VT1529B 173Chapter 5
Notes The 200 kΩ resistors in the recommended divider circuit were chosen so that
the V
SENSE
output voltage from the 5 kΩ reference thermistor will be less than
0.5 V over the temperatures above -15 °C with an excitation voltage of 5 V
or less. (0.5 V is the maximum input voltage that is allowed between the
Sense + and - terminals of the VT1529B.) The thermistor compensation
routines in the VXIplug&play driver assume that the sum of the two resistors
is exactly 400 kΩ. The SENS:REF:THERM:RES:POST command can be
used to specify the actual total resistance value in the divider circuit.
If the combination of excitation voltage and isothermal temperature range
produces divider output voltages greater than 0.5 V, change the resistor
values shown to keep the output voltage below 0.5 V. Also, use the
SENS:REF:THERM:RES:POST command to specify the sum of the
resistor values so that the compensation routines will work correctly.
Figure 5-5. Recommended Reference Thermistor Divider Circuit
Figure 5-6. Recommended Reference Thermistor Field Wiring
Thermistor
+
-
V
SENSE
-
V
EXC
Suggested Wiring for Thermistor Measurement
Note: V should be balanced with respect to groun
d
SENSE
200 k
200 k
+
Ch16
Sense +
Ch17
Sense +
Ch18
Sense +
Ch19
Sense +
Ch16
Sense -
Ch17
Sense -
Ch18
Sense -
Ch19
Sense -
Ch20
Sense +
Ch21
Sense +
Ch22
Sense +
Ch23
Sense +
Ch20
Sense -
Ch21
Sense -
Ch22
Sense -
Ch23
Sense -
Ch20
Ex.Sense +
Ch20
Ex.Sense -
Ch22
Ex.Sense +
Ch22
Ex.Sense -
Ch16
Excitation +
Ch16
Excitation -
Ch18
Ex.Sense +
Ch18
Ex.Sense -
Ch24
Sense +
Ch25
Sense +
Ch26
Sense +
Ch27
Sense +
Ch24
Sense -
Ch25
Sense -
Ch26
Sense -
Ch27
Sense -
Ch28
Sense +
Ch29
Sense +
Ch30
Sense +
Ch31
Sense +
Ch28
Sense -
Ch29
Sense -
Ch30
Sense -
Ch31
Sense -
Ch28
Ex.Sense +
Ch28
Ex.Sense -
Ch30
Ex.Sense +
Ch30
Ex.Sense -
Ch24
Excitation +
Ch24
Excitation -
Ch26
Ex.Sense +
Ch26
Ex.Sense -
Thermistor
Center Sense +
Thermistor
Center Sense -
Thermistor
Right Sense +
Thermistor
Right Sense -
Ground
Trigger