Wildly Fluctuating Pressure Transducer Input [SOLVED]

I just installed a pressure transducer I purchased from an American company called
Transducers Direct. Using Analog Input AO4 on a Uno Wifi Rev2. This is for monitoring a
domestic water line.

The transducer is scaled 0 - 100 psi with a corresponding 0 -5 vDC output signal.

Using a digital multimeter across the input & ground the voltage measures about .820 volts.
It only varies from about .820 to .825 with a stable pressure on the line. I feel like this value is
low since 30 psi should produce an output signal around 1.5 volts if everything is linear. I can live with a deviation and compensate for it in the code but with the large swings in the reading it is not a usable input right now. The input value appears very stable from the meter reading. But the reading goes anywhere from 0 to 80 psi in just a few seconds looking at it on the serial monitor. Since the output is 0 -5 volts with a 0 -100 psi range I just divide the raw input by 10 for the pressure value.

Attached is a wiring diagram of the transducer tied to the UNO. Note: it is using a 16 volt DC seperate power source as the transducer requires 8 to 24 vDC.

edit - the transdurcer is a TDH30CG010003D004 model if you want to look at website:
transducersdirect.com

Your link had some nice pictures but it never got me to the technical details on the transducer. If it is like most I have worked with it has an offset voltage. Measure the output from 0 to full pressure or close to it and see if you get the swing you want. Also you may have a 4-20mA part, I could not find it.

If you click on Datasheets at the bottom the specs are provided.

They do have a model that outputs from .5 to 4.5 volts and can use the UNO 5 volts. I believe they refer to it as "3-wire ratiometric."
I had that spare 16 vDC power pack and decided to power the transducer separately.

I will have to rig up something with a portable air tank to try and get full scale out of it. That is not a bad idea. Tomorrow I hope to talk with the tech support guys at TransducersDirect and see what they think. With what appears to be a stable input signal they may say the UNO is not processing the signal correctly. But that still does not explain the voltage level being low by nearly a factor of two.

for monitoring a domestic water line.

If water is flowing, there will be very large fluctuations in the pressure, due to "water hammer" and the Bernoulli effect. Reliable pressure measurements can be made only during no-flow conditions.

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Understood. I have a valve to isolate the section with the transducer so the pressure is consistent.

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What voltage do you get with no pressure applied?

From my experience transducers seldom (if ever) start at 0 volts. Reason being, electronics doesn't easily have the lower voltage real as a calibrated data point.

Its also a good idea to triple check the connections are correct. Perhaps draw the connector (if there is one). I find if I just look at the connections I'm likely to miss a mistake, so I have to do something different then what I originally did (in verifying the connections).

I had the transducer hooked up in my computer room to another UNO Wifi Rev2
and it read around .2 vDC to atmosphere. You could put your finger on the orifice and it would actually drop down to below .1 after several seconds but never 0.00.

:+1: :+1:... this is one area where I have actually triple verified my connections according to the Datasheet. There is a rubber isolation gasket that slips over the pins that you have to remove to see the pins numbers embossed on the end of the transducer. I also ohmed out the wiring to make sure I had no cold solder joints. I even resoldered the pigtail joints.

What options did you pick? Reading time <10 seconds. Did you get an absolute pressure unit, if so you will have a pressure offset? Did you get a gauge unit there will be no pressure offset but could be a voltage offset dependent on the design.

It is a gauge unit. And there is nothing wrong with the transducer. Read my "solved" message for a laugh.

After talking with Transducers Direct this morning I removed the transducer and rigged up a pressure test with 100 psi from an air tank. The transducer went full scale to 5 volts.

I reinstalled the sensor in the domestic water line and hooked the wiring back up. This time paying more attention to "what went where." The meter reading now was double what it was before.
And after tying it back into the UNO it is within a pound of the analog pressure gauge in the line. And it probably is more accurate than the gauge.

With shipping I paid a liitle over a hundred bucks for this transducer but I think it will hold up over time compared to cheaper overseas sensors available. And it is entirely MADE IN USA.

It is a good thing my retired butt is no longer working in the field because I am just not as sharp as I once was. Time to get a name badge to wear so I can always remember who I am. Lol...

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Welcome to the Club, we have a lot of members they all got initiated the same way as you just did. We also have many bashful members that will not admit there membership. Me I have been initiated many many times (I cannot count that high). Relax and enjoy the benefits.

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