Pressure transducer Scaling Error

[Bob_Schor]

Let's assume that your Sensor is reasonably reproducible (that is, if you put the same pressure in twice, you'll get the same voltage).  You should test this, however ...

So open MAX, and set up a Test Panel for your sensor.  Configure MAX to use whatever "natural units" your sensor puts out, and that are compatible with your DAQ device -- in most cases, this is Volts.  Configure the Range appropriately (if your device is 0-3v, don't set the range to ±10v).

Get Pencil and Paper.  Take a series of readings with pressures from 0 to some reasonable number (let's say 5 Bar, at 1 Bar intervals).  Repeat this to get some idea of reproducibility.  You'd like at least 3 significant figures for your values.

You've just make a Calibration Curve.  I recommend you create a little Excel WorkSheet with these data and post it (I'm very curious, for one thing).  By taking samples over a range of Pressures, you are testing if the Sensor is linear (you're an Engineer -- never assume anything!).

From these data (if you Post them, we can help you with the next step if you need it), you should be able to come up with the Scale Factors that MAX needs.  [I basically described a 2-point procedure at around 2 pm here yesterday).  Once you have them, go back into MAX, set it up to use Scaled Values, and see if the output MAX gives you (in BARs) matches the BARs you read on your Pressure Gauge.

Bob Schor

[Leo1546]

First make sure that the +24 VDC is connected to the transducer's + excitation and -24 VDC to common. Then disconnect the wire that runs form the transmitter's + signal to the control circuit. Now place the voltmeter + lead onto the transducer's + signal and the voltmeter - onto common.

[johntrich1971]

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@Leo1546 wrote:

First make sure that the +24 VDC is connected to the transducer's + excitation and -24 VDC to common. Then disconnect the wire that runs form the transmitter's + signal to the control circuit. Now place the voltmeter + lead onto the transducer's + signal and the voltmeter - onto common.

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Not sure what this has to do with the OPs question. The OP likely has the connections correct, and if he has a +/- 24 VDC power supply connecting +24 VDC to the excitation and -24 VDC to the common would result in 48 VDC. The OP stated he had a 12 V power supply, so he should have 12 V to the transucers excitation and common to common.

[AJ28]

If I have to do perfect connections, which connections should i do, Is it Single referenced with ground or differential connection.

I have a image attached thats how i did the connection. Let me know if that is correct or not.

[johntrich1971]

As shown you have a single ended connection.

[AJ28]

So the connection part is OK.

[AJ28]

Hi John,

Can you please look and tell me how I can do differential connection in this case.

Please let me know.

[Bob_Schor]

Look at the terminals on your USB-6001.  The first four Terminals are Ground, AI0 (SE)/AI0 (+), AI4 (SE)/AI0 (-), and Ground.  The pair at positions 2 and 3 are the + and - inputs to AI0 when you are recording differentially (you need to tell MAX and DAQmx to configure the Analog Input as Differential).  If you specify "Single Ended", then positions 2 and 3 become AI0 and AI4.

You often (but not always!) get better noise reduction if you can record differentially, but you'll only have half the number of differential inputs (since they are pairs) than if you record Single-Ended.

Bob Schor

[AJ28]

Ok.

But I specify RSE and connected signal(2) AI0 and Signal (3) AIGND according to there diagram, is that right?

Just because now, I have to work on more sensors and test the connections with differential (which I am not sure of) to get better signals,I Just need to connect the signal and ground wire from the pressure sensors to the AI0+ and AI0-. Does my supply ground also go to AI0-?

and as I have attached a image can you please look out do we need a resistor as well or not?

Please let me know

Thanks

[Bob_Schor]

If you specify RSE, then you are using Single Ended.  If you have a question about how to wire your sensors, go find a good Electrical Engineer, someone who understands about Signals, Grounds, Ground Loops, shielding, impedance-matching, and get advice from someone who is "hands-on".

Bob Schor