Odd Signal Issue 1

[AtlasND]

I have been working with an Instrumentation technician at my institution for the past few days to install some pressure sensors, and the monitoring equipment necessary to record the signal using Labview. The transducers have 4 pins, 2 for excitation, and 2 for the output signal. While supplying 2.5 V to the excitation, and while our signal stays well within the range of the transducer, the labview code and an oscilloscope are displaying a series of peaks (~20 hz) that rise and fall with the pressure signal (1 hz), though between each peak the signal reads as zero. Also interesting, the signal peaks top off at 10.6 V for a portion of the time between the rise and fall (of the 1 hz signal). The signal is never negative. A multimeter is able to read the signal to be what we expect in frequency and magnitude (although it only reads at 3 hz) I am sorry for the confusing description, but we are confused and I hope someone out there has a suggestion for me to try.

Things we have tried:
using a different transducer
using a transducer from a different company
using a different power supply
using a different DAQ board
using a different Cable
using a different computer
using a different labview code
Running the system in a different room


Please help. Thank you.

 

[danw2]

Wow. Very few people are so diligent as to describe what they've tried in a first post. That rates a star!

Can you take a screen shot or photo of the Y-t trend and attach it to another post (attachment feature is at the bottom of the reply text box)? It's just really hard to trying to put a verbal description to what becomes almost self evident on a Y-t graph.

 

[danw2]

1) What varies from your expectations? The 20Hz jitter? What exactly are you asking for help analyzing?

2) > 2.5 V power supply

A commercial linear or commercial switcher or homemade or ?

3) >transducer
a) brand name and model? Gotta see what its specs are, if any for frequency response, electrical isolation
b) pressure range of the transducer 0 - x ? inches water column? inches Hg? Psi?

4) I take it the oscilloscope is the "analog input" in the system. Which brand/model?

5) >multimeter <snip> reads at 3 Hz

Does that mean your multimeter updates 3 times per second or that when it reads frequency it displays a value of 3Hz?

6) >The signal is never negative.

You made that statement for a reason. Do you expect negative pressures? Is your transducer a compound range that is capable of reporting a negative (vacuum) pressure?

 

[AtlasND]

DanW2,

Thank you very much for your interest in my post, it is the first time i have posted on a forum for help like this, and I am glad to know people are out there and willing to help.

1) the "20 Jitter" was the entire signal there was no other information from the sensor. Also, it was unexpected that the voltage signal was outside the bounds of the excitation

2)We tried a commercial power supply and a battery with a potentiometer.

3)the pressure sensor was an in line sensor from Pendotech, with a range of -7 to 75 PSI

5)the screen updates at 3 times per second

6)The reason I made the statement is that the voltage would go to exactly zero, and stay there for several time points, then jump to 10 V. Really i was stating that this signal could not be any sort of random noise or it would not be regular and it would likely not care about going below 0 volts.

But before you dig too far into any of this new information, we were able to solve the problem. We discovered that the signal was getting saturated, and by grounding every other channel of the input to our computer, we could give the signal a chance to discharge and accurately read the pressure. This is as precise as I can be to the solution, as my technician was able to isolate and discover the problem. I hope this makes sense. Thank you again for your interest in this issue.