1756-if16 and pressure transducer

Hey all,

I need some help. I have a Gefran pressure transducer on our machine hooked to a 1756-if16 analog input card. The transducer is stated at excitation of 6-12 VDC and an output of 3.33mv/v. How do I set this up in RSlogix 5000. There are only choices for -10vdc to 10vdc, 0 to 20ma, 0-10vdc. Any help would be appreciated. I tried using 0 to 10vdc but I'm not sure of the engineering limits etc.

Thanks

You need to buy a pressure transmitter, not a pressure transducer.

Pressure transmitters have conditioned output signals that are conventional industrial signals, like 0-10Vdc or 4-20mA.

Pressure transducers have odd ball outputs, like yours. If your poewr supply to the transducer is a steady (no-ripple) 12.0Vdc, you only get 0.4Vdc output (12.0V * 0.033mV/V) at full scale output. That's an output scale that isn't anywhere close to analog input scales you have available.

Bite the bullet and buy a pressure transmitter that more closely matches your analog input. Pay attention to what power supply it needs and what its output is.

Gefran has transmitters as well as transducers.

Danw,

Ok, thats what I was thinking exactly. I also have some it-612 inputs also free that I could use. Should I use those or just change to a transmitter? However, If I did use the IT-612 inputs the resolution wouldn't be that good right?

Thanks for the help

I wish that A-B would switch to a font with serifs for their user manuals; the thermocouple input module is a 1756-IT6I2.

http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1756-in586_-en-p.pdf


You can run a thermocouple module in millivolt mode so that it doesn't apply any thermocouple linearization math or cold junction compensation.

A thermocouple module has high resolution; the 1756-IT6I2 can go as fine as 0.7 microvolts/bit.

But the total input range is below what you'll get out of this pressure transducer: -12 to 78 millivolts. If your pressure transducer puts out 400 millivolts at maximum pressure, that's too much to measure.


So the final answer is the same: it's best to invest in a pressure transmitter that puts out a standard 0-10V or 4-20 mA instrumentation signal.

Oops, my arithmetic mistake.

3.33mV/V at 12Vdc is 0.040V or 40mV full scale.

So your thermocouple card, with the cold junction disabled, would work.

Use a stable power supply or the output will drift with p/s.

Aha ! Thank you for the correction on the math, Dan.

Thanks a bunch guys

danw said:

Use a stable power supply or the output will drift with p/s.

Click to expand...

A suitable, stable, power supply would probably cost as much as a dedicated transmitter.

And then of course we would be conscious of volt drop in cabling to the transducer.

Much better to have a local panel with a transmitter. That is the typical arrangement, and mostly understood by techs

You could also get an indicator that monitors the pressure, as most have 4-20mA outputs.