I'm wondering what sensors people have used for monitoring pressure, namely negative pressures. Ideally one that fits onto 6mm or 4mm pipe, I can always machine a feedthrough if it's a screw in type.
I have a vacuum pump which feeds to a bell jar-esque enclosure and wish to monitor for leaks - this data can then be used to create a more constant vacuum by re-enabling the vacuum pump and input solenoid, then after a period of time open another solenoid to release the pressure allowing the jar to be opened. I have a system at the moment which is bulky and requires 'user interaction' (pressing a switch at a certain time and monitoring the gauge)
I did a quick google and there seems to be loads of options for positive pressure but not so many for vacuum... it's not something I've done before using the arduino (I have several Nanos).
Plenty of options on Aliexpress if you're happy with no-name sensors with questionable specs.
If you want accuracy at very low pressures then you buy an expensive sensor from a name brand.
Technically there is no such thing as negative pressure, but there are two kinds of pressure sensors: one is differential, and the other is absolute.
Differential sensors measure pressure relative to atmospheric pressure and are called "gage" or "gauge" sensors, while the others are called "absolute" and measure relative to zero.
What absolute pressure range is of interest to you? The lower the absolute pressure that is to be measured, the more expensive the sensor.
You can always use a manometer of the correct length, and fill it with the appropriate fluid. NXP makes a wide range of pressure sensors, I have used them and they are great. You can get differential or absolute whichever you want. I connect them with rubber tubing, it is cheap and easy to do. disclosing the pressure makes it much easier to help you.
jremington:
Technically there is no such thing as negative pressure, but there are two kinds of pressure sensors: one is differential, and the other is absolute.
Differential sensors measure pressure relative to atmospheric pressure and are called "gage" or "gauge" sensors, while the others are called "absolute" and measure relative to zero.
What absolute pressure range is of interest to you? The lower the absolute pressure that is to be measured, the more expensive the sensor.
Thanks for the reply,
I'm looking to measure/control a vacuum between -0.5bar to -1.0bar (absolute). The control side of things is sorted but the vacuum measurement isn't as it's not something I've ever looked into before... accuracy on the measurement can be as high as +_0.1bar so it doesn't have to be super accurate.
I did start looking at some NXP options yesterday and there's just a fair few to choose from! Budget wise £30 or less would be ideal.
The title on the data sheet you linked is misleading, because it gives specifications only for gauge or differential sensors, which have a port (opening) to atmospheric pressure. But that sensor does appear to meet your requirements.
Not ideal package for testing/prototyping but I can always just solder wires to the pins for the moment. There are adapter boards that will convert this to dip. My first try I just used long pins and soldered them across, it was standard IC spacing and plugged into a Dupont socket without any problems.