Analog sensor connection

Hello,

How to connect analog sensor with analog plc module.? Analog sensor has only one output Analog out 4-20mA. Usualy they have two outputs +4-20mA and -4-20mA.

Analog out 4-20mA I connect to I+, but that to connect to PLC Com?

Thank you.

The 0V is the other side of the 4-20mA signal, so your analogue input module and the sensor need to have a common 0V. If the sensor has a separate supply then you will need to connect the two 0V together, if this is not possible or it introduces a common fault then you will have to use a 4-20mA signal isolator.

Without the isolator the 0V from the sensor will go to the sensor power supply and a COM, the 4-20mA goes to an I+ linked across to the V+.

1. Any 4-20mA output has a (+) and a (-) terminal.

For active outputs (powered internally by the field device), the (+) connects to the AI I and AI V terminals, the (-) connects to the COM terminal.

The installation guide notes the jumper between the V terminal and the I terminal for current input wiring.



2. The wiring diagram assumes an active, powered 4-20mA signal.

If the field device generating the 4-20mA signal is loop powered, then field wiring for that device would have to include a DC power supply.

Connections for a loop powered field device:
Power supply (+) connects to field device (+)
Field device (-) connects to AI I and AI V
AI COM connects to power supply (-)

3. There is no such thing as a "negative 4-20mA" signal. For example, vacuum pressure from atmosphere to -1.0Bar is a range of all negative values. But it the signal is a conventional 4-20mA signal.

The 4-20mA can represent a range or scale of negative engineering unit values but there is no (-)4-20mA signal.