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OM-WEB Series User's Guide
Signal I/O Connections
21
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 the pin labeled "NC".
Figure 6. Three-wire RTD or thermistor sensor measurement configuration
When you select a three-wire sensor configuration, the OM-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 on page 22.
You can configure the OM-WEB-TEMP with either a single sensor per channel or two sensors per channel pair.
Four-wire, single-sensor
A four-wire measurement configuration is shown in Figure 7. The diagram on the left shows the sensor
connected to the first channel in the channel pair. The diagram on the right shows the sensor connected to the
second channel in the channel pair.
Note
: There are two high/low channel pairs on each terminal. The #
indicates the channel number. Do not make connections to the pin labeled "NC".