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In this flow control simple experiment in the lab, i am made to control the flow through the pipe and at the same time record down the output given by the sensor in voltage. I am told to record down values for increasing output and decreasing output. The lowest flow is 0cc/min, and highest flow is 3000cc/min. Just wondering why must i take datas for both increasing and decreasing output. Is this so that i can determine the recommended operating range of the sensor? which will be the min. value to the max value of the both sets of outputs (increasing and decreasing) ?

The Objective of this experiment is by the way to investigate the linearity and hysteresis of the flow sensor.

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The Objective of this experiment is by the way to investigate the linearity and hysteresis of the flow sensor.

The key word here is hysteresis: the output of the sensor at the same flow rate might not the same depending on whether you are in the increasing or decreasing output direction. This is why you are being asked to test in both directions. Check out https://en.wikipedia.org/wiki/Hysteresis for more details on hysteresis.

Here's a typical characteristic curve with hysteresis (albeit from a different domain):

enter image description here

You also ask about linearity: it's pretty basic but it means that if you plot your sensor output vs. flow rate, you basically get a straight line if the sensor is linear, or a curved line if not:

enter image description here

If the sensor is linear but has hysteresis, then you'll essentially get 2 parallel lines. If it's linear but without any hysteresis, both lines will be on top of each other and you'll get a unique characteristic regardless of which direction you go.

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  • $\begingroup$ hi, do you know what is linearity in this context then? $\endgroup$ – user185692 Jan 25 '19 at 17:33
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    $\begingroup$ If you don't know what linearity is, then you have no chance with hysteresis... $\endgroup$ – Solar Mike Jan 25 '19 at 21:38
  • $\begingroup$ I have updated my answer to include what is linearity vs. hysteresis. $\endgroup$ – am304 Jan 26 '19 at 12:08

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