Three-Wire Configuration - Measurement Computing USB-TEMP User Manual

USB-TEMP User's Guide Sensor Connections
Two-wire, single-sensor
A two-wire single-sensor measurement configuration is shown in Figure 3-3.
Figure 3-3. Two-wire, single RTD or thermistor sensor measurement configuration
When you select a two-wire single sensor configuration with InstaCal, connections to C#H and C#L are
made internally.
Two-wire, two sensor
A two-wire, two-sensor measurement configuration is shown in Figure 3-4.
Figure 3-4. Two-wire, two RTD or thermistor sensors measurement configuration
When you select a two-wire, two sensor configuration with InstaCal, connections to C#H (first sensor)
and C#H/C#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 3-5.
Figure 3-5. Three-wire RTD or thermistor sensor measurement configuration
When you select a three-wire sensor configuration with InstaCal, the USB-TEMP 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.
3-5