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.
| Standards | Material | TCR | Typical Ro (Ohms) | Callendar-Van Dusen Coefficient | Notes |
IEC-751
DIN 43760
BS 1904
ASTM-E1137
EN-60751
IEC-60751* | Platinum | 3851 | 100
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** | Platinum | 3750 | 1000 | A = 3.81 x 10-3
B = -5.870 x 10-7
C = -4.4 x 10-12 | Low-cost RTD |
| JISC 1604 | Platinum | 3916 | 100 | A = 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 American | Platinum | 3920 | 100 | A = 3.987 x 10-3
B = -5.8686 x 10-7
C= -4.167 x 10-12 | Low-cost RTD |
| US Industrial Standard American | Platinum | 3911 | 100 | A = 3.962 x 10-3
B = -5.8495 x 10-7
C= -4.233 x 10-12 | Low-cost RTD |
| ITS-90 | Platinum | 3928 | 100 | A = 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.