This is the e-mail I sent a NI employee asking for help:
"Thanks
for your help. Our project consists of modifying an air conditioning
system's evaporator coil in order to make the system extract more
humidity from the air. Because the A/C would provide more humidity
extraction the consumer would then be able to set their thermostats at
higher temperature settings and still feel comfortable. This would save
people electricity because the A/C would run for a shorter amount of
time. In theory.
We
will be using thermocouples to measure air temperatures and 4 pressure
transmitters to measure R-22 refrigerant pressures at the compressors.
This is where the NI equipment and LabVIEW come in to play. We have two
DAQs which we will use to acquire the signals from these sensors. The
equipment we possess and plan to use is:
- National
Instruments cDAQ-9172 LegacyNI CompactDAQ Chassis
- National
Instruments 9203 8-Ch ±20mA, 200 kS/s, 16-Bit Analog
Current Input Module
- National
Instruments 9263 4-Channel, 100kS/s, 16-bit, ±10 V, Analog Output Module
- NI USB-6251 Screw Term
The
reason we want to use two DAQs is because the NI SCC-68 has
thermocouple inputs so it is best suited for those sensors. The pressure
transmitters output current which would be best measured using the
cDAQ-9171 chassis with the 9203 current input module. The 9263 analog
voltage output module is required to power the pressure transmitters
since they require a voltage input to operate.
LabVIEW is being used to write the VI which will acquire (and
create) all of these raw signals and turn them into useful data such as
temperatures and pressures. It will also display graphically this data
on a front panel. It will also output all data to a text
file/spreadsheet. We have already created a working VI which acquires
the temperatures from the thermocouples. This VI is working well with no
problems. It is attached to this e-mail.
The problem we are facing is that when we tried to incorporate the
stuff to acquire pressure data from the transmitters it is not working.
LabVIEW is not showing an error which causes the program to not run.
Specifically, the problem we are facing is that all values on the front
panel display NAN. The non-working VI which incorporates the pressure
stuff is also attached to this e-mail. We believe there might be an
issue with LabVIEW trying to use two different DAQs simultaneously."
Also, just in case you were wondering I am using these
pressure transmitters (0-300 psi range). The two wire cable connection
type.
http://www.dwyer-inst.com/Products/Product.cfm?Group_ID=20134&Product_ID=1577&sPageName=Specs
