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I am building an automatic control system for an compressor that stops at a designated pressure. Here's a rough sketch of the system: system diagram The compressor should receive the on signal from the microcontroller until the pressure sensor senses pressure exceeding the set threshold.

However, I have observed that while air is flowing from the compressor to the tire, the pressure sensor reads substantially higher than the actual pressure in the tire. If I turn off the shutoff valve manually, the pressure reads the actual tire pressure.

Is there a way to get the true tire pressure from the pressure sensor while the compressor is on and air is flowing?

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  • $\begingroup$ And a compressor does what? $\endgroup$
    – Solar Mike
    Nov 28, 2022 at 17:37
  • $\begingroup$ put the pressure sensor in the tire $\endgroup$
    – Tiger Guy
    Nov 28, 2022 at 19:15

1 Answer 1

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I have observed that while air is flowing from the compressor to the tire, the pressure I have observed that while air is flowing from the compressor to the tire, the pressure sensor reads substantially higher than the actual pressure in the tire sensor reads substantially higher than the actual pressure in the tire.

That is to be expected. Any flowing fluid will exhibit a pressure drop along the line in proportion to the fluid flow and the resistance. (It's quite analogous to Ohm's law, V = IR.) The tyre valve itself will probably be the highest resistance.

I can think of some options that might help:

  1. Take the pressure reading from a tee right before the tyre valve. It can be piped back on a separate small-bore tube for convenience.
  2. Stop the compressor periodically, measure the pressure and continue.
  3. An advanced form of option 2 is to take to "stop" pressure measurements, calculate the rate of pressure increase (noting that it will be exponential, not linear) and stop close to the calculated endpoint and check again.
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