General questions regarding pressure sensors , needed equipment

[Hemmelig]

Hey

Working on a rather large project and it's the first time I've had to look into the world of pressure sensors.

basically, we're looking into measuring flow levels in small rivers, either in areas where we build a profile to gather up the water and in natural areas where there's no need for construction.

Most of it seems to be pretty straight forward, but there's a couple of things I'm struggling to fully grasp

What type of equipment is needed for submerged pressure sensors ? Is it pretty much a case of getting it to the bottom of the river and fasten it there by using your own preferred method ?

Is there any point in using a differential pressure sensor in rivers ?
basically been looking at absolute pressure sensors and gauge reference pressure.

 

[Baluncore]

Differential pressure is only needed if you are looking for very accurate records that could be affected by barometric surface pressure.

Hydrostatic pressure can be measured by submerging a pressure sensor. But a better way is to keep all the sensor technology above the flood level. To do that, fix any suitable tube in position with the lower end in the water at the depth required. The upper end of the tube is in the instrument housing where a small peristaltic pump pushes filtered air down the tube, so a small bubble rises every few seconds from the deep end of the tube. The air pressure in that tube is sensed at the top or pump end and represents the hydrostatic pressure at the deep end of the tube. The tube can be buried in the river bank, and does not get blocked by growth, while all instrumentation remains dry, above the flood level. The tube diameter, length, and material are not critical parameters, it can be a cheap small bore tube. The tube is easily replaced after flood damage (or vandalism), without any need for re-calibration, apart from getting the depth of the deep-end correctly fixed.