Searching a sensor to measure negative pressure with Genuino Uno R3

Projects Discussion and Showcase Science and Measurement
#1

First of all, sorry, this is not a duplicate post, I just posted it before, but with the wrong account :confused:. I deleted the posts, but it takes 24h before they disapears, and I had to change the title a bit because the forum I used it before, sorryyyyy. So, here the question:

Hello !

For a project, I need to mesure the negative pressure / the succion of small pumps. They are small pumps, with a max succion of probably 500 mmHg (lets even say 1000 mmHg just to be sure). I also need it to capture a lot of data points per seconds, as I want to map the succion patterns with quite a big precision (probably 200 data points per second is ok). I will have to connect the pump to the sensor via a tube, or may be a props to act as the thing the pump is supposed to suck in real life. In another example I saw on a Raspberry (cannot access the specs, too bad), The tube seems to be integrated with the sensor, is there such a thing?

I have a Genuino Uno R3 (from a starter kit), I can probably get around the coding part, but I am completely newbie to the sensor part. I need advice on what I could buy to capture the measures, then I will try to connect it and will probably need advice when I get confused about the cables etc ^_^.

Thanks in advance fo your help!

#2

No worries. There are also moderators who can fix things.
I'm sorry as well, for the cheesy remarks that I will write.

What are "props" ? You are going to the carnival ?
Can you make a drawing ?

The normal barometric pressure is about 100kPa.
If you have a vacuum pump that can pump more than 100kPa, then you can reach completely vacuum.

1000 mmHg = 133 kPa
How can you get a vacuum that is more than complete vacuum ? In what universe is that possible ?

There are two ways to measure vacuum:

  • relative to the atmospheric/barometric pressure with a differential pressure sensor.
  • absolute pressure, for scientific experiments near complete vacuum.

A sensor that can measure near complete vacuum (0kPa) is hard to make. If you don't have to measure more than 500 mmHG, then don't try to do that.

The Arduino Uno is a 5V Arduino board. That matches with a 5V sensor. If you buy a sensor with integrated amplifier, then you can connect its output directly to the analog input of the Arduino.
They are here: https://www.nxp.com/products/sensors/pressure-sensors/vacuum-sensors-50-to-115-kpa:VACUUM_-50-115KPA#/.

[ADDED] The vibrations of the pump can disturb the measurements. The air-vibrations can travel a long way in a tube. You might need a damper. With that, the 200 samples per second might not be needed.

#3

First of all, thanks !

Haha, busted, I wrote 1000 mmHg because I wanted to take margin not to reach the max of the sensor and miss out some data points and completely failed to check the number made any sense.

  • To paraphrase, if I reach a max vacuum of around 500 or 600 mmHg, a differential pressure sensor is more than enough?
  • So in the list, I only take the 5V ones, right?
  • Some sensors in the list mention negative kPa, some positive, does it matter, or can they make both?
  • I don't see the info about having an integrated amplifier in the list, should I open them one by one?
  • Thanks for the vibration info, will consider the damper. That being said, I still need a high measurement frequency because some of the pumps I need to study have patterns with dents / like a staircase, or event with microdrops during the buildup phase, sometimes 10 mini changes over a 0,5s buildup. I suppose i'll this info also on the spec of the sensors?
#4

The most used sensor in that list is the MPX5050DP. I suggest to buy that sensor without thinking, so you can do measurements and tests and get to know everything about your project.

Note: Some pins should not be connected to something. You should leave them open, because they are sometimes connected to the internal circuit.

For the Arduino Uno, you need a 5V sensor. Every sensor in that list has a amplifier. I think you need a differential sensor.

Those sensors have a piezo-silicon-resistive wheatstone bridge inside. Sometimes that can bend in both ways to measure positive and negative pressure. Sometimes it can bend only in one way.

When a sensor is a differential sensor, it has two ports (DP = Dual Port). If it can only measure a positive pressure, then one port can be open (ambient air) and the other port can measure a positive pressure. However, if the other port is open then it can measure negative pressure.

Can you search for: arduino, sensor, ratiometric
The Arduino has default the VCC (or AVCC) as reference voltage. That is the 5V pin of the Arduino board. The analogRead() returns 0...1023 relative to the 5V pin.
The sensor is ratiometric, it outputs a value relative to the 5V that is used to power the sensor.
That means if you power the sensor with the Arduino 5V pin, then the "ratiometric" magic happens.

The MPX5050DP can measure up to 50kPa. That is only 50% vacuum. You need more.
Can you find a sensor with a larger range ? Perhaps you can combine the MPX5050DP with a absolute pressure sensor or a sensor from another brand.

#5

Couple of points - if the sensor is connected via length of tubing , it is highly unlikely you will see changes in reading at a rate of 200 per second.
You need to define how accurately you want to measure vacuum and buy the appropriate transducer .

You probably need to google vacuum sensor or absolute pressure transducer .

#6

Thanks a lot @Koepel and @hammy, I have some Googling to do, I will post back when I a more knowledgeable about the sensors!

#7

In my opinion you have some buying to do. Buy the MPX5050DP. You need to use it to get some feeling for how everything works and behaves.

#8

Aaaand no one has it in stock. If can find some but rated for 10-16V, or 5V but only 10kPa.