Creating Virtual Channels for RTDs in NI-DAQmx and Traditional NI-DAQ

Updated Jun 29, 2018

Reported In

Hardware

  • PXIe-4357

Driver

  • NI-DAQmx
  • Traditional NI-DAQ

Issue Details

How do I create a virtual channel in Measurement & Automation Explorer (MAX) for my RTD using NI-DAQmx, and how is it different from a Traditional NI-DAQ virtual channel?

Solution

In Traditional NI-DAQ, the scaling is set when you select the RTD Standard you are using. In NI-DAQmx, the RTD-defining characteristics are used to set the scaling instead. This removes confusion about multiple names for the same RTD type. The table below lists the RTD types available in NI-DAQmx. This list is also included in the NI-DAQmx Help located at: Start»Programs»National Instruments»NI-DAQ.
 
StandardsMaterialTCRTypical Ro (Ohms)Callendar-Van Dusen CoefficientNotes
IEC-751
DIN 43760 
BS 1904 
ASTM-E1137 
EN-60751
IEC-60751*
Platinum3851100 
1000
A = 3.9083 x 10-3 
B = -5.775 x 10-7 
C = 4.183 x 10-12
Most common RTDs including Pt100
Low-cost vendor compliant RTD**Platinum37501000A = 3.81 x 10-3 
B = -5.870 x 10-7
C = -4.4 x 10-12
Low-cost RTD
JISC 1604Platinum3916100A = 3.9739 x 10-3
B = -5.870 x 10-7 
C = -4.4 x 10-12
Used primarily in Japan
US Industrial Standard D-100 AmericanPlatinum3920100A = 3.987 x 10-3
B = -5.8686 x 10-7 
C= -4.167 x 10-12
Low-cost RTD
US Industrial Standard AmericanPlatinum3911100A = 3.962 x 10-3
B = -5.8495 x 10-7 
C= -4.233 x 10-12
Low-cost RTD
ITS-90Platinum3928100A = 3.9888 x 10-3
B = -5.915 x 10-7 
C= -3.85 x 10-12
The definition of temperature
*EN-60751 and IEC-60751 are international equivalent standards.
**No standard. Check the TCR.

In NI-DAQmx, instead of choosing between four standards for the RTD type as in Traditional NI-DAQ, you can choose the actual RTD type, such as Pt 3750. You also can select the external wiring configuration—2-wire, 3-wire, or 4-wire. Selecting the nominal resistance value (Ro), excitation current source, and excitation value is the same as in Traditional NI-DAQ.

If you do not want to use a virtual channel or task, there is a built-in LabVIEW VI for scaling instead—the Convert RTD Reading VI located on the Signal Conditioning palette.

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