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I have an MPX2102DP pressure sensor. I have designed a simple instrumentation amplifier using the OP07 amplifier to read the output (differential pressure) of this sensor.

From the datasheet, I have found that there is a signal for each pressure. Can I obtain the reading of each pressure value alone from the instrumentation amplifier?

I have attached the diagram of the instrumentation amplifier.

enter image description here

JRE
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Ayman hussien
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2 Answers2

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This sensor has a full scale span of only 40mV and an output impedance of 3k max.

Although you have shown a typical high gain INA config. You omitted tolerances which have a great effect on CM noise rejection. I suggest you use high precision R’s or get a real INA chip with 100 dB CMRR.

There is no spec for the Vdc nominal or independent output accuracy, so I doubt that will work as expected with conversion from differential pressure to differential voltage. I.e. these are not two independent sensors in series rather just one differential sensor (converted to single ended electrical then to differential drive.)

Tony Stewart EE75
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  • I was using AD620 instrumentation amplifier. However, using band bass passive filter to reject the noise is a must (I did not show that in the schematic) But I am trying this idea because I want not only the differential pressure value, but also the values of the low pressure and high pressure. if I can obtain these results from this sensor, how can I do that? like the marks that I showed in the schematics? or there is another method to obtain these signals? – Ayman hussien Aug 13 '21 at 23:59
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From the datasheet, I have found that there is a signal for each pressure, ...

I think you have misunderstood the datasheet. The sensor is available in three versions.

enter image description here

  • The single-port versions have the port exposed to atmosphere and the pressure differential is relative to the pressure in the sealed port (presumably some gas sealed into the device).
  • The dual port version has each side exposed to a port.

... so can I obtain the reading of each pressure value alone from the instrumentation amplifier?

No, the dual port sensor has no internal reference pressure. Imagine the use case where it is being used to monitor the pressure drop across an air filter in a pressurised line:

  • Port 1: upstream measurement pressure = 2 bar.
  • Port 2: downstream measurement pressure = 1.7 bar.
  • Pressure differential: 0.3 bar.

The sensor will be able to report the pressure difference but cannot give the absolute pressure (pressure above 0 bar) or the gauge pressure (pressure above 1 bar) as there is no reference signal available.

enter image description here

Figure 1. The sensing element appears to be a Wheatstone bridge device.

The differential signal is probably derived from a Wheatstone bridge circuit. Differential output allows the device to handle positive or negative pressure differentials while powering the device on a single rail supply.

Transistor
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  • Thank you for your answer. I have another idea (it may be strange). Can I add a reference pressure to the sensor, in order to read signals from it? if it is available how can I do that? – Ayman hussien Aug 14 '21 at 09:04
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    I think you need to ask a new question. Draw a diagram of how you think this would work. I suspect that you're going to need two sensors one port of each vented to atmosphere and the others connected to whatever you're measuring. You'll need a differential amplifier for each to give the two pressures relative to atmospheric and a third to get the difference between those two. – Transistor Aug 14 '21 at 09:15
  • If I will use another sensor, so no need to add a third sensor. Because I can measure the absolute pressure by joining low pressure branch to the atmosphere. after that I will deal with each signal alone in the software. – Ayman hussien Aug 14 '21 at 10:38
  • That sounds good. – Transistor Aug 14 '21 at 10:47