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# Accuracy of a pressure sensor function of flowrate

## Accuracy of a pressure sensor function of flowrate

(OP)
Hello,

I need a suggestion about how to calculate the accuracy of a measurement system. In particular the system is an hydraulic circuit in which a fluid flows through silicone tubes and cross some filters. I need to calculate the pressure at the inlet of a filter. A pressure sensor with an accuracy of +/- 50 mmHg is present before the filter and a flowmeter to measure the flow rate is available as well. Between the pressure sensor and the filter an electrovalve is present that causes a pressure drop. To characterize the pressure drop, an external pressure sensor has been introduced at the inlet of the filter and a curve has been calculated at different flow rates. So the final pressure at the inlet of the filter has been calculated as:
Final Pressure = P1 - DeltaP where:
P1: pressure measured by pressure sensor present in the hydraulic circuit
DeltaP = A* FlowRate^2 + B*FlowRate + C (where Flowrate is read by the flowmeter sensor and A,B and C are parameters characterized as described above). The flowsensor has an accuracy as well.

I would like to figure out how to better estimate the total accuracy of the Final Pressure, considering it is the set of the accuracy of the pressure sensor, the flowmeter sensor used to calculate the pressure drop and maybe the accuracy of the external pressure sensor used to characterize the curve.

Thanks

### RE: Accuracy of a pressure sensor function of flowrate

I'm lost, too many conflicting descriptions. I may not be able to help, but a sketch of what is where in this piping would be of assistance.

### RE: Accuracy of a pressure sensor function of flowrate

You would need to know the rated accuracy of the pressure sensor and flowmeter used in the test that developed the correlation. You could then estimate the possible variation (at worst case +/- tolerances for measured flow and pressure) of the final pressure.

### RE: Accuracy of a pressure sensor function of flowrate

Pressure drop across a filter is not a constant. They get plugged with time.

### RE: Accuracy of a pressure sensor function of flowrate

What type of flow meter do you have ?
Assuming the valve opening is fixed, fluid density is fixed for all flows, then from flow hydraulics,
DP = K. V2, where K is a constant, V is line velocity, and assuming flow is well into the turbulent regime for all flows ( say Nre > 10e3 )
so in your correlation, terms B and C should be either zero or very small.
Why is measurement accuracy so poor for these 2 pressure sensors? Usually, pressure measurement accuracy (with electronic pressure transmitters) is much better than that for flowmeters.

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