NI 4351, CB-68T, LV 7.0, Incorrect Temperatures
Tim_in_Kingston
Our group is trying to get our thermocouple board working under
LabVIEW 7.0. So far we can not get the thermocouple to function
correctly under MAX, or the Temperature VI example provided by NI.
We are using:
Windows 2000 (all latest updates installed)
LabVIEW 7.0
PCI 4351 card
CB-68T Isothermal board (inside a CA-1000 Configurable Connector
Accessory Enclosure)
Driver: NI-DAQ Version 7.2 for Windows 2000/NT/XP
LabVIEW 7.0 has been freshly installed in a new computer, and no
previous older drivers for the NI 4351 have been installed.
I will break down the question into a few sections so that it can be
referenced to easier.
All thermocouples used are K-type.
1) Using Measurement & Automation Explorer (MAX)
I tested the thermocouples and voltage readings. The thermocouple was
left in the ambient air (~ 22 C), and the voltage was tested using a
AA battery (1.6 Volts measure with a multi-meter). All thermocouple
measurements were done on Ch 9, voltage measurements were done on Ch
10.
Under MAX, to setup up the thermocouple board, I selected Traditional
NI-DAQ, then selected the NI 4351.
a) Choosing CB-68T from Properties -> Accessory
Temperature: measures incorrect temperature value. (-15 C)
Voltage: measures correct voltage. (1.6 V)
b) Choosing None from Properties -> Accessory
Temperature: Measures temperature value of 17 C. Close to the
room temperature.
Voltage: Measures the correct voltage. (1.6 V)
2) Using NI Example: NI 435x Thermocouple.vi
Results are similar selecting either CB-68T or None in MAX under
Properties, then Accessory.
a) Selecting Cold Junction Compensation (Ch 0)
Temperature reading for the selected channel reads: NaN
b) Selecting User Specified
Temperature reading is about 280 - 300 C. A value that is very
incorrect.
All cables are firmly attached to the PCI card and the CA-1000
enclosure. All thermocouple leads are firmly attached to the board.
Thank You,
Tim.
Adam U.
I am a little concerned that you mention picking a device that is not
the 4351. Where did you select this device? What device did you
select.
As far as the CJC goes, it sounds like we may have a bad CJC setup on
our hands. Let's try measuring the CJC voltage itself (channel 0) and
seeing whether this voltage is in the correct range or not. Also,
let's measure channel 1 (the auto-zero channel) as this should have
little or no voltage on it. If both of these readings are in the
correct range we may have a software problem but I believe the problem
is on the hardware side. Notice the second-to-last note on page 8 of
the user manual at: http://www.ni.com/pdf/manuals/321613b.pdf. I would
like to ensure that these switches are in the cjc position.
Let me know how this comes out.
Have a great day!