Programming instructions

Chapter 21 Common SCXI Applications
© National Instruments Corporation 21-7 LabVIEW Data Acquisition Basics Manual
diagram below shows how you can program the Acquire and Average VI
to measure the amplifier offset. You can find this VI in
vi.lib\daq\
zdaqutil.llb
. This VI acquires 100 measurements from the amplifier
offset, designated in the
offset channel
input by
calgnd
, and then averages
the measurements. When you determine the amplifier offset, you must
always use the same input limits and clock rates that you will be using in
the acquisition. The Acquire and Average VI can measure the amplifier
offset of many modules at once, but in Figure 21-2, it only measures one
module.
Figure 21-2.
Measuring a Single Module with the Acquire and Average VI
After measuring the amplifier offset, measure the temperature sensor for
cold-junction compensation. Both the amplifier offset and cold-junction
measurements should be taken before any thermocouple measurements
are taken. To measure temperature sensors, you use the Acquire and
Average VI. The main differences between the amplifier offset
measurement and temperature sensor measurement are the channel string
and the input limits. If have set the temperature sensor in
mtemp
mode
(the most common mode), you access the temperature by using
mtemp
.
If you have set the temperature sensor in
dtemp
mode, you read the
corresponding DAQ device onboard channel. Make sure you use the
temperature sensor input limits which are different from your acquisition
input limits. To read from a temperature sensor based on an IC sensor or
a thermistor, set the input limit range from +2 to –2 V.