Hi there,
i wonder if I could get some guidance from you guys. I am building a vacuum chamber, which I intend to try and control the pressure of via arduino. I mean to have a servo turn a toggle on/off on the pump to do this, but the machine needs sto know when to turn on/off. I am wondering, is there a noob-friendly way to have the arduino take a reading of the pressure level, and receive it as workable input?
Check this thread: pressure sensor
The OP has built a model submarine and is adding an arduino to control it. This thread relates problems he's having with depth sensing, apparently because the sensor he has so far only measures pressures less than atmospheric. That sensor might be a good start for getting the pressure in your vacuum chamber.
If I'm reading the specs on that one correctly, it says it has a limit of 20 kpa, which is a very low level of vacuum. I'd be needing something which preferably would go down to like 5 pascals (the limit of my small, single stage vacuum pump). Is such a thing truly nonexistent?
I seem to recall some air conditioning duct systems as used in commercial installs use vacuum switches to detect air flow, usually around a venturi so perhaps if you know someone in that arena.
Something from there?
Link dead.....
Just google "vacuum gauge".
Here is one that measures 0-1600 Pa http://www.davis.com/Product/Digital_vacuum_gauge_0_to_12000_0_to_1_600_Pa/YX-68101-00?referred_id=3388&gclid=CPaXm_T1h8ICFQWTfgodCFQAYQ
Far beyond that, you can buy ionization vacuum gauges that measure down to 10^-9 Pa
Will this work?
http://www.mksinst.com/product/product.aspx?ProductID=442
Will this work?
No.
5 Pa = 0.04 torr which is below the lower measurable limit of that sensor (0.1 torr).
Get an ino gauge then. You want to play with vacuum. It will not be cheap.
Hi, atmospheric pressure is about 101,325 pascals or 101 kPa.
So you cannot have a vacuum guage that measures lower than -101kPa.
Tom.... 
Greensprings:
hook a load or deflection sensor to a diaphram inside the chamber
it should be easy to calibrate, a small increase in vacuum should create a large mechanical deflectioneverything doesnt have to be electronic
What kind of material to make that diaphram? Will it be stretched across a port on the chamber?
I'd be needing something which preferably would go down to like 5 pascals (the limit of my small, single stage vacuum pump). Is such a thing truly nonexistent?
This SDP600-25Pa / SDP610-25Pa differential pressure sensor has ±25 Pa range, 0.1 Pa + 3% of reading accuracy, 0.03 Pa repeatability, 12-bit resolution.
dlloyd:
This SDP600-25Pa / SDP610-25Pa differential pressure sensor has ±25 Pa range, 0.1 Pa + 3% of reading accuracy, 0.03 Pa repeatability, 12-bit resolution.
Have you read this?
The highly sensitive chip requires only a minuscule amount of gas flow through the sensor.
This is for HVAC, not for vacuum. You can use a differential pressure sensor in 1ATM but this one is not fit for vacuum. What is the reference you have to give it to read absolute pressure only with a 500Pa range? The picture shows nozzles that are fit for rubber hoses, not vacuum fittings that I've been used to.
This is for HVAC, not for vacuum. You can use a differential pressure sensor in 1ATM but this one is not fit for vacuum.
Looks like I've incorrectly interpreted the requirement as going down 5 pascal (vacuum) "from atmospheric", not going down all the way to an "absolute pressure" of 5 pascal.
If the requirement is to measure ultra-low vacuum from atmospheric, then this sensor could be used as stated here. Also, it requires a low level of air flow to work:
❝ A vacuum is any pressure less than the local atmospheric pressure. It is defined as the difference between the local atmospheric pressure and the point of measurement. A vacuum is correctly measured with a differential pressure transducer that has one port open to atmosphere. If, for example, the negative port is connected to a vacuum and the + port open to atmosphere, the transducer signal will increase as the vacuum increases. It will always indicate the correct vacuum, even when the local atmospheric pressure changes. ❞
A mechanical pump can produce some decent vacuum for some applications. Ultra"-"low vacuum requires several types of pumps. First run mechanical pump until the pressure won't drop anymore (in torr or millitorr range). Then start a turbo molecular pump to get to 10^-6 torr. After that, burn some expensive platium wires in a sublimation pump to get to 10^-9 to -11 torr. Now THAT is an Ultra-HIGH vacuum 
Ohhh my kingdom for a turbo molecular pump 
! But I digress, that's for a different project.
Thank you all so much for the responses,
I have been continuing to look around for a suitable sensor, but I believe my all-encompassing parameters are unrealistic for my shoestring budget, and are now seeming like overkill. Allow me to explain, I am building a freeze drying machine, which I would like to have controlled by Arduino. This means I only truly need a measurement down past the triple point of water (611 Pascals absolute) with a reasonable amount of wiggle room below that (say, down to a couple hundred Pascals absolute). Budget is definitely the limiting factor for a poor college kid, but pinpoint accuracy is not essential. The plan is to have the Arduino regulate the vacuum to where it can sublimate water, and give a reading.
With that in mind, does anyone have any ideas?
Thanks!
It doesn't seem like an aneroid barometer would work very directly, apparently the mechanisms are stiff, and require a literal tapping to jar them into place. anyway, that still doesn't help much in terms of interfacing with an Arduino. Anyone have any ideas on how such a gauge could be created?