Calibrated flow source

A project log for VISP - Ventilator Inline Sensor Package

Bidirectional flow (volume), pressure, and temperature sensing in a single inexpensive I2C/SPI package.

Daren SchwenkeDaren Schwenke 04/11/2020 at 15:172 Comments

We need to generate a coefficient for our sensors when attached to out pitot tubes.  To do that we need to have a precise source of airflow.

The current thought process is leaning towards pvc pipe with a piston in it.  Move the piston down the pipe and your are displacing a known volume of air, which we can send through our sensor and calibrate it.

Problem is for a 4in pipe and using 5/16in threaded rod (18 tpi) , that rod would need to spin at 8k rpm to move fast enough to hit our upper target for flow.  Move to a 6in pipe, and use 1/2in threaded rod (9 tpi) and that number is a lot more reasonable 2k rpm.  

Working on it.


chris wrote 04/16/2020 at 14:53 point

You don't need to calibrate the airflow to a specific value, you just need to know what the actual value is.  So you just need an accurate measurement of actual volume per second.  You don't need to force the airflow to a specific value.    So use a weighted piston to push a known volume of air through the sensor.  Use a valve to restrict the air flow,  measure the time it takes to move that volume and you have a flow rate.  That gives you the data point for that flow rate, then change the valve and do it again.  Do it a few times and you'll get a curve (I don't think this will be linear).  No motors or lead screws required.

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Daren Schwenke wrote 04/16/2020 at 15:02 point

Good example/point.  We will look at that.  Thank you.

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