Sensing low relative air pressure? (sensitive manometer sensor) Buy or make? - Page 1
Forum section: electronics / projects

author: cdev
author_rank: Super Contributor
timestamp: December 09, 2016, 02:55:28 pm
content: I would like to figure out a way to sense fairly low relative air pressures for use in HVAC. The pressures are likely very low. Does anybody know of any commercial products that can sense very low relative pressure between two points? (not barometric pressure per se but barometric pressure might work as the air will flow from areas of higher pressure to lower pressure.) Cost is an issue, I am on a tight budget. (I could also measure capacitance of a piece of foil allowed to move in two directions using an AVR, which would be cheap!).Accuracy on relative strength isn't so important but accuracy as to when zero pressure exists is. Ideally a sensor would be able to sense pressure in both directions. Any ideas would be very welcome.

author: jpanhalt
author_rank: Super Contributor
timestamp: December 09, 2016, 03:01:36 pm
content: Check our Magnehelic flow/differential pressure gauges. Here is one vendor so you can see approximate new prices. Cheaper ones probably available.http://www.dwyer-inst.com/Product/Pressure/DifferentialPressure/Gages/Series2000John

author: cdev
author_rank: Super Contributor
timestamp: December 09, 2016, 04:19:29 pm
content: Yes, they are definitely the HVAC industry standard!Do you make sensors, that don't have the costs associated with an instrument housing/dial, etc?

author: nfmax
author_rank: Super Contributor
timestamp: December 09, 2016, 04:55:13 pm
content: Many years ago, I did a proof-of-concept prototype of a low cost differential sensor for HVAC. It used a cheap and cheerful differential pressure sensor, and got round the zero pressure drift problem by periodically using a 2-way solenoid valve to remove the pressure input & 'short' the two sides of the sensor together, and auto-zero the circuit (using a DAC). The valve was powered from a big capacitor which was slowly charged up from the 4mA standing current part of the 4-20mA loop output. It worked OK, but never got taken up. Probably you can get better quality differential pressure sensors these days, anyway.

author: max_torque
author_rank: Super Contributor
timestamp: December 09, 2016, 06:16:09 pm
content: Define "Low pressure"??Off the shelf delta pressure sensors exist that can sense something like 1000 Pa full range, so with say a 10bit adc you should be able to get a resolution of 1 Pa (depending on how fast you need to sample the pressure of course)

author: cdev
author_rank: Super Contributor
timestamp: December 09, 2016, 08:40:24 pm
content: I would guess that if I used something like a Magnehelic it likely would be the lowest magnitude scale that I would use. That low. So low as to be almost silent.The best thing I could do is get some low cost sensors that are as sensitive as I can find, or build one, and experiment.

author: mk_
author_rank: Regular Contributor
timestamp: December 10, 2016, 10:24:08 am
content: Quote from: cdev on December 09, 2016, 02:55:28 pmwe are using Type 401 "very low pressures" (Page 13)https://www.hubacontrol.com/fileadmin/user_upload/domain1/Produkte/Uebersicht_EN.pdfMichael

author: mjkuwp
author_rank: Unknown
timestamp: December 10, 2016, 12:43:58 pm
content: I don't have any special knowledge about this but I wonder if it is roughly what you are looking for.Pressure Sensor ±0.004 (±0.025 kPa) Differential Male - 0.2" (5.2mm) Tube, Dual 16 b 3-SIP Modulehttp://www.digikey.com/product-detail/en/sensirion-ag/SDP610-025PA/1649-1037-ND/5872275