Measurement-computing USB-TEMP-AI Manuel d'utilisateur télécharger pdf (Page 14)

USB-TEMP-AI User's Guide Signal I/O Connections

Two-wire, two sensor

A two-wire, two-sensor measurement configuration is shown in Figure 5.

Figure 5. Two-wire, two RTD or thermistor sensors measurement configuration

When you select a two-wire, two sensor configuration with InstaCal, connections to T#H (first sensor) and

T#H/T#L (second sensor) are made internally.

When configured for two-wire mode, both sensors must be connected to obtain proper measurements.

Three-wire configuration

A three-wire configuration compensates for lead-wire resistance by using a single voltage sense connection.

With a three-wire configuration, you can connect only one sensor per channel pair. A three-wire measurement

configuration is shown in Figure 6.

Figure 6. Three-wire RTD or thermistor sensor measurement configuration

When you select a three-wire sensor configuration with InstaCal, the USB-TEMP-AI measures the lead

resistance on the first channel (T#H/T#L) and measures the sensor itself using the second channel (T#H/T#L).

This configuration compensates for any lead-wire resistance and temperature change in lead-wire resistance.

Connections to T#H for the first channel and T#H/T#L of the second channel are made internally.

Three-wire compensation

For accurate three wire compensation, the individual lead resistances connected to the ±I# pins must be of equal

resistance value.

Four-wire configuration

With a four-wire configuration, connect two sets of sense/excitation wires at each end of the RTD or thermistor

sensor. This configuration completely compensates for any lead-wire resistance and temperature change in lead-

wire resistance.

Connect your sensor with a four-wire configuration when your application requires very high accuracy

measurements. Examples of a four-wire single-sensor measurement configuration are shown in Figure 7 and

Figure 8.

You can configure the USB-TEMP-AI with either a single sensor per channel or two sensors per channel pair.

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Measurement-computing USB-TEMP-AI Manuel d'utilisateur Page 14