Pressure transducer and Differential flowmeter

Discussion in 'Homework Help' started by HUMBLE, Oct 29, 2010.

1. HUMBLE Thread Starter New Member

Oct 24, 2010
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This is a practical assignment .I have conducted the experiment and got value for Flow meter pressure and corresponding Voltage readings.I have also got the transducer Pressure and corresponding voltage.

My problem is how to deal with question : Determine the relationship between voltage and pressure and Voltage and flow rate .

And in the later case determine theoretically the flow to enable a transfer function to be determined in respect of flow and voltage.

Please kindly shed light on this

2. Kermit2 AAC Fanatic!

Feb 5, 2010
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Do a quick plot on graph paper and see if it is a LINEAR relationship.

(the same amount of increase in one parameter causes the same amount of increase in the other, at high and low end of flow meter scale.)

3. HUMBLE Thread Starter New Member

Oct 24, 2010
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I have done that and found that the graph for the Pressure transducer gave a straight line.But that of the Differential flow meter is not quite a straight line.

I have included the graph that i have plotted for the differential flow meter and the pressure transducer

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5. HUMBLE Thread Starter New Member

Oct 24, 2010
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I am looking at the bernouli equation with a view to getting the transfer function.
thank you thus far.

I really appreciate

Mar 6, 2009
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7. HUMBLE Thread Starter New Member

Oct 24, 2010
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I am looking at it .But I want to find out if there is any equation(s) that relates flow rate,Voltage and pressure.

Thanks

8. t_n_k AAC Fanatic!

Mar 6, 2009
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You appear to have the relationship between the flow meter output and pressure differential for a range of unknown flows.

The flow meter must have a known scale relationship for the actual flow and a corresponding output voltage. Do you have that scale relationship? If not you can't develop the overall function.

9. Kermit2 AAC Fanatic!

Feb 5, 2010
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Yes, You must know the details of the meter. What is its lowest output and its highest output and at what flows these two points occur. These two points must be included in the math of any formula you will develop, along with your data on the relationship at other flow rates between the extremes.

10. Kermit2 AAC Fanatic!

Feb 5, 2010
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Hint: a formula that uses the log function will usually have squared terms and a resulting sq rt term in the answer.

11. HUMBLE Thread Starter New Member

Oct 24, 2010
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I showed my lecturer what I have done so far and he said ,'first the graphs have to be a straight line,then I should look at the slope with a view a coming out with a relationship for voltage and pressure;and voltage and flow rate.

He then added another bit that was not give in the before to help in this .The diameter of the input from the compressor side is 11.3mm.The goal is to determine the flow rate of the set up form the result of graph plotted.

12. t_n_k AAC Fanatic!

Mar 6, 2009
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The graphical information you have given so far would only allow someone to come up with a notional relationship between pressure and voltage.

That's all we could do for you in the absence of any other data. The compressor side diameter may be of interest but I would think you'd need more information.

A linear fit for your data is possible but it's a stretch of credibility to take that as the truth.

A rough transcription of your data gave me a linear fit of

V=0.041+0.091*P

A 3rd order polynomial fit gave

V=-0.5+0.36*P-0.035*P^2+0.0014*P^3

which was the "best" fit of the data.

You could do an exponential fit

V=1.6*(0.77-e^(-0.18*P))

Or a natural logarithmic fit

V=-0.27+0.53*ln(P)

I used an application called "CurveExpert" to do this.

The options are manifold and the linear fit doesn't rate highly.

Is there anything else you can tell us about the experiment or other relevant data?