Wiring a 3-wire prox sensor to Rio

Here is some connection information for connecting a 3-wire proximity sensor to the Rio channel 0.

Here is a link to the prox sensor. IFM model IGS249
https://www.ifm.com/ca/en/product/IGS249

WIRING THE PROX TO THE RIO
Configure the Rio channel 0 as a 5-30 VDC Digital Input.
Connect the Prox BN (brown) wire to the +24VDC power supply.
Connect the Prox BK (black) wire to the Rio terminal 1.
Connect the Prox BU (blue) AND the Rio terminal 2 to the Common of the 24v supply.

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EQUIVALENT CIRCUIT
IFM provides a wiring diagram which could use a little interpretation.
The small rectangle shown between the BK and BU wires represents the Rio. For channel 0 on the Rio, that is terminals 1 and 2.
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The IFM specs show the prox is a PNP device.
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The RIO’s DC Discrete input on channel 0 is like a photodiode. It passes current in one direction and it turns on the internal circuits through an optocoupler for isolation.
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Here is the channel shown on the Rio’s wiring chart.
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Here is a crude equivalent circuit.

Tracking the flow of current through the circuit: When the prox trips ON, the PNP transistor acts like a switch, which allows the current to flow from the +24vdc power supply, through the prox and through the input circuit on the Rio, finally back to the common side of the power supply.

Note: The BU wire on the prox also needs to connect to the common of the power supply. That wire is not shown below.
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WIRING A 3WIRE PROX TO THE RIO.zip (334.8 KB)

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