beautypg.com

Figure 3. fp-rtd-124 input circuit, Taking measurements from four-wire rtds, Figure 4. four-wire rtd connections on one channel – National Instruments cFP-RTD-124 User Manual

Page 5: Taking measurements from three-wire rtds

background image

© National Instruments Corp.

5

FP-RTD-124 and cFP-RTD-124

Figure 3 shows the input circuitry on one channel.

Figure 3. FP-RTD-124 Input Circuit

Taking Measurements from Four-Wire RTDs

Four-wire RTDs generally have two wires of one color and two of
another color (usually red and white). Connect the wires of one
color to the positive terminals (EXCITE+ and SENSE+). Connect
the wires of the other color to the negative terminals (COM and
SENSE–).

Figure 4. Four-Wire RTD Connections on One Channel

Taking Measurements from Three-Wire RTDs

NI recommends the [c]FP-RTD-122 for three-wire RTD
measurements because it includes special sensing circuitry to
compensate for up to 95% of the lead resistance of the third wire.
Most three-wire RTDs have two wires of one color (usually red,
sometimes black) and one wire of another color (usually white,
sometimes red). Connect the two wires of the same color to the

SENSE+

[c]FP-RTD-124

SENSE–

COM

EXCITE+

Amplifier

Pulsed 2 mA

Four-Wire

RTD

16-bit

ADC

SENSE+

[c]FP-RTD-124

SENSE–

COM

EXCITE+

Four-Wire

RTD

This manual is related to the following products: