Three-Wire Configuration; Four-Wire Configuration - Measurement Computing USB-5200 Series User Manual

USB-5203 User's Guide Sensor Connections

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-5203 measures the lead resistance on
the first channel (C#H/C#L) and measures the sensor itself using the second channel (C#H/C#L). This
configuration compensates for any lead-wire resistance and temperature change in lead-wire resistance.
Connections to C#H for the first channel and C#H/C#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-5203 with either a single-sensor-per-channel, or a two-sensor–per-channel pair.
Four-wire, single-sensor
A four-wire, single-sensor connected to the first channel of a channel pair is shown in Figure 7.
Figure 7. Four-wire, single RTD or thermistor sensor measurement configuration
A four-wire, single-sensor connected to the second channel of a channel pair is shown in Figure 8.
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