Hi,
I have an old GWR transmitter which need to be connected to Mark-Vie. The transmitter specification says that it provides output signal of 4-20mA and a power supply requirement of 48VDC over 2 wire.
The Mark-Vie analog input card provides a bias voltage of 24VDC.
Is there a conversion transducer or a circuit which helps me connect a 48VDC powered analog input to a AI card which can only accept 4-20ma input with bias voltage of 24VDC?
Thanks.

 

You need a loop isolator. There are different flavors of isolators, depending on whether the output side is active or passive, whether the isolator itself is loop powered or DC powered.

The Transmitter side has to be capable of handling 48Vdc of loop power.

THe Mark-Vie side has to be passive, expecting to be powered from the Mark-Vie 24Vdc power supply.

 

Hi David,
Thanks for the reply. Do you know of any particular make/model of isolator which has the capability to provide such functionality?
Thanks.

 

Hi All,
Is there any particular transducer or isolator which has the capability to provide 48VDC on transmitter side and connect to 24VDC on PLC side? Please help with make / model if any.

Thanks.

 

Use your preferred World Wide Web search engine and look for "loop isolators."

I can also recommend a DC-DC converter, such as ones made by Phoenix Contact and many other manufacturers, that will convert a 48 VDC input to 24 VDC output, and you can use that for just about any loop isolator.

If you're connecting a 4-20 mA transmitter to a Mark VIe, generally there are terminals on most 4-20 mA inputs that can accept a 4-20 mA input which is powered by the transmitter and NOT powered by the Mark VIe. Look at the PAIC I/O Pack section of Vol. II of GEH-6721 on the various types of terminal boards which can be connected to the terminal boards. They generally can accept two-wire inputs (loop-powered), three-wire and four-wire inputs (externally powered devices).

 

I don't understand if you have a 48 VDC supply or not. And if it's output is 4-20 mA and the transmitter provides the power for the regulated current, you can connect the output of the transmitter to the 4-20 mA and Return terminals of any 4-20 mA input as shown in 'Externally powered transmitter wiring 4-20 mA' drawing--presuming the transmitter is a four-wire device as shown in the drawing. If you need 48 VDC I suggest you get a DC-DC converter that converts 24VDC to 48VDC and use that to power the device and connect its output as shown in the referenced drawing. Be sure to set the hardware jumpers properly.

Look at all the drawings for the terminal board you select (I'm just showing the TBAI for the PAIC I/O Pack). Usually the dropping resistor for the 4-20 mA input is 250 ohms, which will produce 1-5 VDC for 4-20 mA.

But I'm NOT familiar with transmitters that require 48 VDC, and how the output works. I'm presuming the circuitry in the transmitter will vary the current per the measured signal and it doesn't care what the dropping resistor is, as long as its usually less than 500 ohms. BUT, since we don't know anything about the transmitter you're on your own.

That's all I can do. If you don't have a 48 VDC source you could probably use a 24 VDC output from an unused input channel for a 24 VDC to 48 VDC DC-DC converter (I'm sure somebody makes one of those) if the device needs 48 VDC. (Phoenix Contact QUINT-PS/24DC/48DC/ 5 DC-DC converter.) Then if the device output can drive a 4-20 mA circuit with a 250 ohm dropping resistor you'll be good.

Let us know how this works out.