Looking for a vacuum sensor preferably digital but analog to 5V is also ok - Page 1
Forum section: electronics / projects

author: Kjelt
author_rank: Super Contributor
timestamp: June 02, 2016, 10:04:41 am
content: Hi,I have built my own vacuum setup in the past, it contains of a Festool vacuum pump, a vacuum glass storage flask as a vacuum buffer and a controller that monitors the vacuum with a vacuumswitch and switches on off the pump and all the valves.What it simply does is on startup run the vacuum pump wait for a couple of seconds then opens the valve between the pump and the flask measuring with a simpel vaccuum switch that switches on at -0,8 bar , at that stage I close the valve , shut off the pump and open another valve to release the vacuum on the pump.Then it is quiet and I can use the three outputs for desoldering or my vacuum pincet tooling and perhaps in the future my manual P&P machine, who knows.The problem is in the switch, it only detects one vacuumlevel which I set at -0,8 bar at which point I switch off the pump. But when to turn the pump back on is actually a kind of random event. I count the seconds the valves for the desoldering or pincet are used and I take a safe bet when to activate the pump again. Not very scientific.So I want to improve. I want to measure the vacuum level continuously and let the user decide at which level it should be activated again (for the pincet I do not use -0,8 bar, as even -0,4 bar is sufficient.) thus resulting in more quiet periods in between.So my question: who knows a nice vacuum sensor from 0 to -1 bar ?All I can find are honeywell sensors with differential voltage outputs to 10V not what I am looking for.Probably some small niche firm should have nice sensors for this purpose? Can't seem to find them.Since the sensor will be interfaced with a 5V microcontroller , i preferably would like a digital output or 0-5V analog is also fine.Thanks

author: H.O
author_rank: Frequent Contributor
timestamp: June 02, 2016, 10:21:35 am
content: How about theMPX5100D(P)?It's not really a vacuum sensor but a differential pressure sensor, I think that it'll work for what you're doing.Oh, and if you want I2C then perhaps something like theNPA700Bseries will work.

author: Andy Watson
author_rank: Super Contributor
timestamp: June 02, 2016, 11:29:53 am
content: I have been pondering a similar project for some time and not really found a good solution.I've just seen these:http://uk.farnell.com/sensonor-technologies-as/83715/ic-sensor-pressure-comp-sp300/dp/1845360although, the fact that they are in the Farnell clearance sale suggests that they might be end-of-line.

author: Kjelt
author_rank: Super Contributor
timestamp: June 02, 2016, 12:19:43 pm
content: Quote from: H.O on June 02, 2016, 10:21:35 amThat it is differential is not a problem if there are two tube connections, since I am not sure if a negative pressure (vacuum is actually a negative pressure) can be measured by those sensors.So if I switch the two inlets and leave the normal high pressure input open to the normal airpressure and the vacuum on the other side it would measure the difference as a positive pressure which is fine.

author: Kjelt
author_rank: Super Contributor
timestamp: June 02, 2016, 12:35:23 pm
content: Quote from: Andy Watson on June 02, 2016, 11:29:53 amThanks.In the datasheet I can only find it to measure positive pressure to 1 or 2 bar (model dependent), nice find but not sure if I am allowed or even can use that for vacuum.

author: Wolfram
author_rank: Frequent Contributor
timestamp: June 02, 2016, 12:47:46 pm
content: Quote from: Kjelt on June 02, 2016, 12:35:23 pmIt's important to distinguish between gauge pressure and absolute pressure. Gauge pressure is measured relative to atmospheric, so a vacuum is approximately - 1 bar (dependent on the local air pressure) and atmospheric pressure is 0 bar. When measuring absolute pressure, a perfect vacuum is 0 bar, and atmospheric pressure is approximately 1 bar (dependent on the local air pressure).This is an absolute pressure sensor, and since the datasheet says it measures from 0 to 1 bar absolute, that means it goes down to a vacuum.

author: Kjelt
author_rank: Super Contributor
timestamp: June 02, 2016, 01:10:41 pm
content: Thanks for clarifying , that is an important thing to know when choosing the sensor. Thanks

author: HighVoltage
author_rank: Super Contributor
timestamp: June 02, 2016, 04:18:11 pm
content: There are many automotive type vacuum sensors on the market with pretty linear output quality0 to -1 bar0 to 5V DC outputThe repeatability is also pretty good but the absolute value might not be so good.If you make a calibration table of your own, they should be reliable enough for what you are trying to doThey come for many different values of vacuum and outputHere is one example from Bosch

author: TerraHertz
author_rank: Super Contributor
timestamp: June 04, 2016, 07:37:30 am
content: This. Saw an ad for these recently, and will buy some when I can afford. (They are pretty cheap!)http://au.mouser.com/new/measurement-specialties/msi-ms5837-30ba/?utm_source=GlobalSpecDatasheetPromoter&utm_medium=display&utm_campaign=teconnectivity-msi-ms5837-30ba&utm_content=supplier-branded-728x90Mouser Part #: 824-MS583730BA01-50Manufacturer Part #: MS583730BA01-50Manufacturer: Measurement SpecialtiesFrom their advert:QuoteIt's not clear to me yet how these would attach to plumbing/chamber. Also would much prefer something with flying leads rather than directly mounting on a PCB. But that's not a big deal.The pdf datasheet includes register details and reading software algorithm.I like these because they are tiny, cheap, probably good enough for vacuum pumping system sequencing control, and the gel fill allows sensors with virtually zero gas volume. Whether the gell is compatible with high vacuum, don't know yet.

author: MadTux
author_rank: Frequent Contributor
timestamp: June 04, 2016, 08:12:40 am
content: You have a company name and absolutely no money?Go here and order a free sample:http://porter-inficon.com/It's a real nice sensor, gives 0-10V for 0-1000mBar. Other ranges are also available

author: DTJ
author_rank: Super Contributor
timestamp: June 04, 2016, 08:35:51 am
content: Visit your motor disassembler wreckers and grab a manifold pressure MAP sensor. Cheap and effective.

author: Kjelt
author_rank: Super Contributor
timestamp: June 04, 2016, 03:20:43 pm
content: Quote from: TerraHertz on June 04, 2016, 07:37:30 amThanks for sharing but too good for my purpose, 100mbar accuracy is more then enough for my purpose, 10mbar would already be luxury.Quote from: DTJ on June 04, 2016, 08:35:51 amThanks for the tip , I went two hours ago. I am not sure if it was due to the place I visited (it looked like sh*t so I thought they would be cheap), but the oldest and cheapest they could offer was one sensor without cableassembly/connector for €20.-No datasheet or visible markings where to put the 12V and the ground and what was the output, a weird (car standard probably) connector I do not own so I decided to pass.They had newer ones with connector, around €60 for the (used) sensor and another €80 for the cable assembly with the connector. Hmmmm then I would rather go to Farnell and buy one with a datasheet

author: calexanian
author_rank: Super Contributor
timestamp: June 05, 2016, 12:31:44 am
content: We use the Honeywell 26PC series of sensors at 5 volts with great success. They are ratio metric and the 10 volt spec is for temperature regulation purposes. They can be run at 5 volts with good accuracy so long as the tenperature of the case of the device does not vary to an extreme amount. The temperature variation of your average day will be of little consequence.