Measurement Computing WEB-TEMP - Manual (Page 19)

WEB-TEMP User's Guide Signal Connections
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Figure 5. Two-wire, two RTD or thermistor sensors measurement configuration
When you select a two-wire, two sensor configuration, 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 6. Note : There are two high/low channel pairs on
each terminal. The # indicates the channel number. Do not make connections to pin marked "NC".
Figure 6. Three-wire RTD or thermistor sensor measurement configuration
When you select a three-wire sensor configuration, the WEB-TEMP measures the lead resistance on the first
channel (between Ix+ and C#L) and measures the sensor itself using the second channel (between C#L and Ix-).
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 WEB-TEMP with either a single sensor per channel or two sensors per channel pair.