Measuring Pressure with NI9205 in RSE Mode

[Omid82]

I am using NI9205 module for measuring pressure, but when I connect two pressure transducers to the module in RSE mode there is a drop in signal output of pressure transducer and when I dissconnect it the signal come back to the previous value, also when I use differential mode after few second the signal output turns to 50Hz oscillation,can you please help me?

the pressure transducers are PDCR 4011, 200mV output and needs 10V supply and  I am using two similar power supplies for transducers.

thanks

Omid 

[Adam G]

Hello Omid,

I was wondering what happens when you use a multimeter to measure the voltage output of your transducer? Also if you have a known voltage source hooked up to the 9205, such as a battery or a power supply, does the signal drop when connected?

Best Regards,

Adam G 

[Omid82]

Hi Adam

Values given by multimeter are the same value when I connect just one pressure transducer to the module in RSE mode, as you said I connected the power supplies to the module in RSE mode the values are the same and there is no drop in signal

thanks

Omid

[Adam G]

HI Omid,

I'm a little confused on your last post. Could you post the values you get when measuring with a multimeter and the values you get when reading with the 9205 and also the values they are suppose to be. Also what values do you get when you attach a known voltage source to your device? Do you get the same result if you use different channels?

Best Regards,

Adam G 

[Omid82]

Hi Adam

 Sorry for the confusion in last post, actually I think I've solved the problem I just wanna know your idea about that

I am using a two wires which are shielded for connecting pressure transducers to NI9205 ,at the first stage I set up the system in differential mode, the signal was ok for few second but after that the signal turned to 50Hz oscillation, then I went for RSE mode it was ok for one pressure transducer, but  for two, when I shared the COM connection, the values were different, so I moved back to differential mode and tried to get rid of 50Hz oscillation I read the NI tutorial for "Field wiring and Noise Consideration for analog Signals" and used two bias resistors solution and it worked, 50Hz disappeared. When I was working on the bias resistors I noticed the wire shield is not connected to anything and I connected the shield to the COM of the module and it is working well with two pressure transducer, so at the moment I am using differential mode and wires shields are connected to the COM, do you think unconnected shields were the problem? 

Sorry for the long post

 Thanks

Omid 

[Adam G · Accepted solution]

Hello Omid,

It does sound like the shields were inducing the 50Hz noise you were seeing. They could have been picking it up from some other equipment in the room, and I think grounding the shield is the correct solution for the problem.

Best Regards,

Adam G