connecting 4-20 mA pressure transdxr to scxi 1327

[gohuskies]

I am having trouble connecting a 4-20 mA pressure transducer to a scxi 1327 terminal block with an 1125 signal conditioner. i have a 3 wire ( + - G) coming off of the transducer and only a +/- connection on the terminal block.  currently i have it connected just with the +/- and the ground is not connected at all.  when i set up a daqmx task and test the sensor I get zero no matter how much pressure is in the sensor.  has anyone set up this configuration before that could give me some insight on what to do? I havent dealt with pressure and the 1327 blocks before. thanks.

[garretth]

Hello,

You will definetely need to make sure that you are making a current measurement since your transducer is 4-20mA output. The SCXI-1328 has special resistors that make this measurement possible. However, the 1327 is not equipped with these resistors. You can connect your transducer to a known resistance and then just make a voltage measurement around the load. Definetely check the manual for your transducer. All pressure transducers are different, but the manual usually provides a schematic on how to connect them to a DAQ device.

[gohuskies]

I also have a 1328 available, but don't i need a power source for a reference? the 1328 doesnt have a reference supply like the 1520 does it?  i am trying to figure out what the best way to measure pressure with a 4-20 mA output sensor.  I have four 1125s with 1327s and an extra 1328 as well.  I dont really want to spend $2500 on a 1520 if i dont have to but i need some way of getting a power source into the signal.  would this work with an external 0-10 V supply? if so, how would you wire it?  thanks, this is all very new to me, obviously, I'm a mech e, not an EE.

[garretth]

Unfortunately, the SCXI-1125 is not equipped to supply the excitation for your pressure transducer. You could, however, just use an external supply as you mentioned. I would think that the manual for the transducer would show a diagram for connecting a power supply. There should be either a (+) and (-) or a (+) and (GND) where you should connect your external power supply to your transducer. Check the manual to know for sure.