hello,

I have a question about a pressure transducer , its output is in the form of a current signal varying between 4 and 20 milliamps , with the following wiring diagram.

the module has only two wires coming out of it , connected as descriped in this firure , I wonder how there is no ground wire to the module , and what would this ground sign circled in blue be connected to .

or does the module act like a varying resistance that changes as the pressure changes , hence changing current ? but the datasheet says that the direction of the wires cant be reversed , so it cant be simply a resistance.

this is the datasheet link
http://www.gemssensors.com/en/Produ...dia/GemsNA/InstructionBulletins/203022-a.ashx

 

This is a 4-20mA current loop module.

It is an electronic device that controls the current through the device. It uses a transistor to regulate the current and hence it is sensitive to voltage polarity, i.e. you cannot reverse the connections.

It does not require a ground connection.

 

...or does the module act like a varying resistance that changes as the pressure changes , hence changing current ?

That's one way to think about it. It's self powered by the voltage across its inputs. The few I've dealt with were not able to operate in reverse - they were polarity dependent. I suppose one could be designed to self-adjust.