With a pressure sensor mounted I could now start testing what pressure readings were returned for the low heads expected during operation of the Wastop.
I plugged in the sensor to the analogue input on my Ardunio UNO and ran a simple program which returned the direct output from the sensor (a value from 1 to 1050) via a laptop and set the serial output plotter running.
The photo above shows my son Max getting amongst the testing, being a big fan of water play there was plenty of splashing going on. We poured in water to the top of the 500 mm tall riser pipe to see what values were returned.
With the sensor just submerged I got a reading of 99, while when full to the brim I got only 102.
This range of only 3 for a water height difference of 500 mm indicates that the sensor I'm using has a pretty low resolution.
In a worst case, we may get up to 5 m of head behind the valve, and we need to be able to measure pressures of at least 20 mm difference in order to accurately determine the flows passing through the valve.
The sensors I have were a generic pressure transducer from AliExpress and after some further digging I found that they were actually rated for 1.2MPa which is about 120m of water head, way above what we needed.
It took some digging to find an alternative supplier, then even more to find a suitable sensor and connector which would work at the 5V that the Arduino operates at.
This fancily named Telemechanique sensor from Element 14 should fit the bill, and with a 1 bar rating (10m of head) it should have enough resolution for us to tell what is going on upstream and downstream of the check valve.
It also has a detailed data sheet which will be very useful as I calibrate the sensor.
At $260 all up it wasn't cheap, but it is a critical part of the development so I went ahead and ordered.
I can barely contain my inner geek waiting for it to arrive so I can plug it in and test the resolution!
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