Pressure transducer input difficulties

[ELake]

I'm using a SC-2345, USB-6251 and SCC-SG24 modules. I'm also using Dynisco brand pressure transducers with a range from 0-10,000psi. Output is 3mV/V. I'm using the 832 series Transducer, here is a link.. http://www.dynisco.com/products/mc/manuals/974039.pdf
The problem I'm having is that my readings fluctuate big time when I view my data.. It fluctuates from -10m to 60m. (when reading voltage) I'm using high quality belden shielded cable and I've double/triple/quadruple checked all of my connections.
I can read 2.40V (but still hunting all over) when the shunt cal is active on the Transducer..

Other questions -
Should I read my inputs as voltage or should I read them as Strain?
What is the easiest way to scale my output? I'd like to take my output readings and scale them to PSI.

Thanks in advance
ELake

[johnsold]

ELake,

1. What kind of readings do you get if you connect a battery operated voltmeter to the transducer output?

2. Have you checked for power line frequency interference, possibly showing up as common mode voltage?

3. If you take a small battery (AA size) and connect two resistors to generate a 10 - 20 mV signal and connect that to your system with the transducers disconnected, do you get a stable result?

4. How many transducers do you have and how are they attached to the apparatus being tested? What kinds of motors are used to drive the pumps which produce the pressure?

I suspect that you are getting power line frequency interference. It could be due to ground loops, inductive pickup, leakage currents, or other causes.

Lynn

[ELake]

Just checked the output with a Fluke 789, reading is .002V @ 0psi, simulated 80% (shunt cal) = .026V
I haven't installed any of the transducers yet, I'm just in the infant stages of setting this up. Bascially this setup will be used to check various pressure regions of a high pressure, high flow hydraulic valve. We used to use Measurement Computing stuff but this new application requires some pre-trigger sampling.

Any suggestions on how I can eliminate the noise?

[johnsold]

I am not familiar with your hardware, so I cannot be of much more help. It sounds like you may have something configured incorrectly.

Lynn

[J_Thomas]

Hi Elake,
Here is a document you might want to look at to help solve the noise issue:

Field Wiring and Noise Considerations for Analog Signals


You asked in your first post about measurement setup and scaling. One common way of setting up this type of measurement is to use a NI-DAQmx Custom Voltage with Excitation Task.  You can then set up a custom scale to convert the voltage reading to a PSI reading.

If after reviewing the above documents, you still can’t figure out what is going on, I have a few questions for you:

1. I am a bit confused about the noise you are seeing in your measurement. In your first post you mentioned that your signal fluctuates from -10m to 60m and you can read 2.40V (but still hunting all over) when the shunt cal is active on the Transducer. In you second post you mentioned “Just checked the output with a Fluke 789, reading is .002V @ 0psi, simulated 80% (shunt cal) = .026V. I haven't installed any of the transducers yet.” Do you have the transducer installed yet? What signal are you trying to measure? Is it possible that the signal itself is noisy?
2. Could you provide a detailed description or diagram of how you have your signal connections? What slot is the SCC-SG24 installed? How do you have your wires connected?
3. What are you using to take your measurements?  A test panel in Measurement & Automation Explorer (MAX) for your device or task? A LabVIEW program?
4. What settings do you have configured in software?
5. Have you tried Lynn’s suggestion to try testing your setup on a known voltage with your transducer disconnected?