Hey all,

I've got a little project to do. we want to be able to monitor our hydrogen line's pressure from one of our offices. I think the best way to go about this would be to use a wireless pressure transducer, instead of running cable from where we store our hydrogen to the office we want to be able to see the data from. the distance just seems a little ridiculous for such a thing.

The transducer I'm looking at is a low power radio transmitter, transmits a 4-20 signal, and gets picked up by a receiver. What I'm lost on is how one would go about taking that signal from the receiver and inputting it to a PLC. Anyone have any experience with such a thing?

Thanks guys

 

Hi,

I guess it all depends on the kind of receiver and transmitter that you're using. Which radio signal are you planning to use?

It is common to build a mesh using wirelessHART or ISA100 protocols, which shouldn't be difficult to interface to a PLC. Most gateways have an OPC server. But I don't know if a mesh of that type applies to your project.

Furthermore, what about using 3G? Connect the 4-20 mA to a microcontroller or a PLC supporting 3G and Modbus and you're done (you may even try an Arduino for this).

 

If you already have a pressure transmitter, then by far, the simplest method to get a signel into a PLC is a pair of radios that whose function is wired-in/wired-out. When you wire 4-20mA to an input on one end, you get 4-20mA output on the other end.

In the USA, Banner Engineering and Phoenix Contact both sell a pair of wired-in/wired-out radios (along with others, I'm sure).

If you need a battery powered pressure transmitter, then you're in the Wireless HART or ISA 100 wireless game.

But neither provides an analog output. Either's gateway (at the office end) presents field data in Modbus registers, which are accessible with an OPC server if you want the field data in an HMI or SCADA. A PLC with a Modbus master could fetch the data from the gateway.

The ante-up costs to just get into the HART/ISA100 wireless game is about 6x-8x that of a pair 'electrician's radios'.

Even if you need to run some wire to get DC power to the field transmitter/field radio, it'll be less costly than getting into HART/ISA100 for a single point. Banner has battery powered field radios, but the field pressure transmitter needs power.