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Connecting 4..20 mA sensors

4..20 mA current output sensors can be connected to the MonoDAQ-U-X using external shunts.

For accurate and precise measurements the usage of 50 Ohm shunts is recommended since they allow the MonoDAQ-U-X’s 1V voltage range to be used fully.

Up to 8 sensors can be connected when single-sided voltage measurements are used and up to 4 can be connected when differential voltage measurements are used.

Wiring schematics

Single sensor

Below are shown the wiring schematics for all three common types of current output sensors (2, 3 and 4-wire).

All single sensors are shown connected in differential voltage measurement mode. This way there is no need to worry about any voltage drops due to signal wire resistance.

The differential mode should be used when efficient use of available channels is not a concern. In this way, only a total of four sensors can be connected.




Multiple sensors

The same wiring can be utilized to enable multiple sensors to be connected to the U-X

The example shown uses 3-wire sensors but the logic is the same for all sensor types.

For anything more than two sensors an external power supply should be used.

Four differential measurements

A schematic with four four-wire sensors connected in differential measurement is shown.

Full sensor isolation could be achieved by using separate power supplies for each (four-wire) sensor.

Eight single-ended measurements

The maximum amount of sensors connected to the U-X is shown. All sensors are 3-wire.

Since a single potential (GND) is used for all shunts care must be taken that the wires connecting the low side of the shunts together are kept short (low resistance). Otherwise, errors due to the internal resistance of the wires could present an error.

Note that having all sensors be the same type is not necessary. Two-wire, three-wire, and four-wire sensors can all be used together with the same U-X device.

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