Four-wire, two sensor common terminals (4W01 to 4W67). Omega OM-USB-TEMP

OM-USB-TEMP User's Guide Sensor Connections

Four-wire, two sensor common terminals (4W01 to 4W67)

These terminals are used as the common connection for four-wire configurations with two RTD or thermistor sensors.

Two sensor common terminals (IC01 to IC67)

These terminals are used as the common connection for two-wire configurations with two RTD or thermistor sensors.

Ground terminals (GND)

The six ground terminals (

GND

) provide a common ground for the input channels and DIO bits and are isolated

(500 VDC) from the USB GND.

Power terminals (+5V)

The two

+5V output terminals are isolated (500 VDC) from the USB +5V.

Digital terminals (DIO0 to DIO7)

You can connect up to eight digital I/O lines to the screw terminals labeled DIO0 to DIO7 . Each terminal is software configurable for input or output.

CJC sensors

The OM-USB-TEMP has two built in high-resolution temperature sensors. One sensor is located on the right side of the package, and one sensor is located at the left side.

Thermocouple connections

A thermocouple consists of two dissimilar metals that are joined together at one end. When the junction of the metals is heated or cooled, a voltage is produced that correlates to temperature.

The OM-USB-TEMP makes fully differential thermocouple measurements without the need of groundreferencing resistors. A 32-bit floating point value in either a voltage or temperature format is returned by software. An open thermocouple detection feature is available for each analog input which automatically detects an open or broken thermocouple.

Use InstaCal to select the thermocouple type (J, K, R, S, T, N, E, and B) and one or more sensor input channels to connect the thermocouple.

Wiring configuration

Connect the thermocouple to the OM-USB-TEMP using a differential configuration, as shown in Figure 3.

Figure 3. Typical thermocouple connection

The OM-USB-TEMP

GND

pins are isolated from earth ground, so connecting thermocouple sensors to voltages referenced to earth ground is permissible as long as the isolation between the GND pins (9, 19, 28, 38) and earth ground is maintained.

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