1734-IE4C with isolated signals

[A_G]

I am trying to use the 4-20 mA signals from a device whose user manual says that it outputs "isolated 4-20 mA". I only have spare PLC inputs in a 1734-IE4C. This is for Non Isolated analog signals according to its manual. i decided to try it anyway. I wired from the "+" device mA to the card, and from the "-" device mA into my 0 VDC common in the electrical control cabinet. This 0 VDC common is not grounded, in case this matters. I do see some values in the PLC around 4.3 mA but I know it should be reading more like 15 mA right now. Can this be because 1734-IE4C is a non isolated input card? Can I make it work somehow? Do I need to buy another card (that is for isolated signals) and if so which one? (I tried googling it but didn't come up with anything, I'm new to Point IO). Thanks in advance!

 

[parky]

Normally, isolated output means the sensor or converter has an isolated output in other words it contains a form of optocupler so the supply of the sensor is isolated from the output, it means the ouptput needs to be supplied by the analogue input card, i.e. 2 wire wiring where the card supplies the voltage in the 4-20ma loop.
So a non isolated card is fine. not knowing what the device is (I suggest you post tghe make/part number).
In essence the sensor will need a 24v supply the analohue card then needs to be active i.e. you supply 24v from the card (or other source) in a 2 wire configuration In the case of the analogue card the supply for the 4-20ma signal is sourced from the cards internal bus i.e. 4 wire configuration as in this manual for 4 wire connection

1734-IE4C | Allen-Bradley

POINT I/O 4 Point Analog Input Module

www.rockwellautomation.com

 

[JesperMP]

Measure with an V-meter directly on the input + and - leads to the device. Do you have the required 24V ?
Measure with an mA-meter directly on the output + and - leads from the device. Do you get the expected 15 mA ?

An isolated transmitter can work with a non-isolated PLC input.
You just have to figure out the path for the current signal to and from the transmitter.

This 0 VDC common is not grounded, in case this matters

If the 0 VDC is the same used for the transmitter and the PLC it should be OK.

 

[A_G]

Normally, isolated output means the sensor or converter has an isolated output in other words it contains a form of optocupler so the supply of the sensor is isolated from the output, it means the ouptput needs to be supplied by the analogue input card, i.e. 2 wire wiring where the card supplies the voltage in the 4-20ma loop.

Good to know, I always thought that "isolated" just means "separate common" and "non isolated" means "shared common".

In essence the sensor will need a 24v supply the analohue card then needs to be active i.e. you supply 24v from the card (or other source) in a 2 wire configuration In the case of the analogue card the supply for the 4-20ma signal is sourced from the cards internal bus i.e. 4 wire configuration as in this manual for 4 wire connection

The device is a "Prismatic Trace Gas Analyzer" instrument, attached is a screenshot of the user manual where it shows how to wire the device connector. I do not see where the +24 VDC supply is supposed to go. I will ask the vendor if I need to wire +24v to the device and if so then where.

Measure with an V-meter directly on the input + and - leads to the device. Do you have the required 24V ?
Measure with an mA-meter directly on the output + and - leads from the device. Do you get the expected 15 mA ?

I will try this

Thank you both!