Incorrect pressure bridge sensor readings in NI9237 Module

[OxSanj]

I have connected Kyowa Pressure bridge sensors BEC-D-1MPA to a NI-9237.  These bridge sensors have an initial bridge unbalance 0.436 mv/V shown on the calibration sheet and a rated capacity of 0.315 mv/V at 1MPa.  The resistance of each sensor is 120.2 Ohm and these have 4-wires (2 input and 2 output). I have selected excitation of 2.5V and plugged in scaling of 0 mv/v@ 0 Pa and 0.315 mv/V @ 1E6 Pa.  The calibration constant is 0.318MPa / 1mv/v.  Using the example vi for pressure bridge sensors I select null offset, which zeros the initial reading. Unfortunately, as I apply increasing pressure I get readings with an increasing gain for each pressure. I am using only two ports of the NI-9237 so unlikely exceeding a power consumption limit of 150mW. I am unclear whether any jumpers are needed for the RS-/RS+ and SC connections as per the NI9237 instructions? Or this is handled by software null offset.

Not sure, how to resolve this. 

[oxsanj1]

I have connected Kyowa Pressure bridge sensors BEC-D-1MPA to a NI-9237.  These bridge sensors have an initial bridge unbalance 0.436 mv/V shown on the calibration sheet and a rated capacity of 0.315 mv/V at 1MPa.  The resistance of each sensor is 120.2 Ohm and these have 4-wires (2 input and 2 output). I have selected excitation of 2.5V and plugged in scaling of 0 mv/v@ 0 Pa and 0.315 mv/V @ 1E6 Pa.  The calibration constant is 0.318MPa / 1mv/v.  Using the example vi for pressure bridge sensors I select null offset, which zeros the initial reading. Unfortunately, as I apply increasing pressure I get readings with an increasing gain for each pressure. I am using only two ports of the NI-9237 so unlikely exceeding a power consumption limit of 150mW. I am unclear whether any jumpers are needed for the RS-/RS+ and SC connections? Or this is handled by software null offset.

Not sure, how to resolve this. 

[santo_13]

Please share the connection diagram.

You must connect all wires for best performance,

[OxSanj]

Hello Santo13

The connection diagram and description are unclear as to what needs to be connected.  May I ask you to kindly clarify please?

Thank you.

[GerdW]

Hi Ox,

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@OxSanj wrote:

The connection diagram and description are unclear as to what needs to be connected.

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Which connection is "unclear" in the diagram?

Why do you ask for any "jumpers": there are no jumpers in the diagram…

[OxSanj]

Hello Gerd,

The full bridge sensors have only 4 wires - red (+excitation),  black (-excitation), Green (- Output signal) and White (+ output signal) which are connected to AI+, AI-, EX+ and EX-. The NI-9237 operating instructions and spec state "for a full bridge you must connect the AI+, AI-, EX+, EX and RS+ and -RS signals".  Kindly see Figure 3 of the NI-9237 (with RJ50). I have RS+ and RS- left unconnected, I am using an example vi with null offset and no shunt. But I end up with readings that require gain adjustment. Hence confusion prevails..

best wishes

Oxsanj

[GerdW]

Hi Ox,

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@OxSanj wrote:
The NI-9237 operating instructions and spec state "for a full bridge you must connect the AI+, AI-, EX+, EX and RS+ and -RS signals". 

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What happens when you connect RS+/RS- with EX+/EX-, respectively?

[OxSanj]

Hello Gerd

Thank you for your response. 

When I connect RS- with EX- and RS+ with EX+ the response of the pressure sensor is a flatline on the test panel.

Without the connections with RS+ and RS- the response of the sensor is as shown below 

The operating instructions state the following and provide the connection diagram. You must connect AI+ and AI-, EX+ and Ex-, and RS+ and RS- signals. However it fails to indicate what to connect with? Just poor wording...

The instructions indicate options to correct for resistance errors: remote sensing and shunt calibration. Per your suggestion I have followed Figure 4 and I get a flatline....

Thank you again for your guidance.

Oxsanj

[GerdW]

Hi Ox,

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@OxSanj wrote:

The operating instructions state the following and provide the connection diagram. You must connect AI+ and AI-, EX+ and Ex-, and RS+ and RS- signals. However it fails to indicate what to connect with? Just poor wording...

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All the connections are shown in Figure 3: how does that image "fail"?

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@OxSanj wrote:

The instructions indicate options to correct for resistance errors: remote sensing and shunt calibration. Per your suggestion I have followed Figure 4 and I get a flatline....

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Figure 4 is just a "boil down" of Figure 3 for those 6 connection lines…

Can you test your sensor with a simple power supply and a DMM?

Can you provide a datasheet of your sensor? I couldn't find one for the type number given in your first message.

(And please keep discussion in one place.)

[santo_13]

Are you applying a varying pressure signal to consider a flatline reading from DAQ as bad?

If you're not applying any "varying" pressure signal, a flatline is a clean reading from DAQ.