Selection of pressure sensors for wind tunnel

Projects Discussion and Showcase Science and Measurement
1

Hey guys,

For a project we are supposed to measure the air pressure in a wind tunnel at different measuring points of an object by means of several differential pressure sensors.

At the measuring points there is a maximum differential pressure of ~200Pa, i.e. 2mbar.

For this purpose, we were given the specification for the selection of the sensors that they should not exceed an inaccuracy of 1%.

We were provided with the following sensors for testing purposes:
2x MPX2010DP, 2x MPX2100DP, 2x MPX2050DP and 2x MPX53DP.

Now after further research and some testing with these sensors we found out that all of them are not really suitable for our project, unless you would work with an instrumentation amplifier.

In other threads, the MPX5010DP data sheet MPX5010DP was used for similar applications, since this already brings a built-in amplifier with it and thus also a much higher sensitivity. Now, according to the data sheet, this also has an inaccuracy of 5% and would therefore again not fit our specifications.

Since we are absolute beginners in this topic, we now have the following questions:

What exactly does the sensitivity value of 450mV/kPa (MPX5010) mean in contrast to 0.4mV/kPa (MPX2100) data sheet MPX2100DP ?

Which sensor is best suited for our application? Do we prefer to use one of the sensors provided to us (including an instrumentation amplifier), or do we prefer to use an MPX5010DP directly, for example?

2

The 5% accuracy of the MPX5010 is the overall accuracy, including the amplifier. That is pretty good for these sensors. Add 0.5% for the Arduino and the total will be 5.5%.
It is a 10kPa sensor. You need an other sensor to measure up to 200Pa.

Does the datasheet of the MPX2010DP tell what the overall accuracy is ? Perhaps all the numbers should be added. If everything is added together and the instrumentation amplifier accuracy is added as well, then I think it will be more than 5%.

You need a instrumentation amplifier for the provided sensors. I think that is part of the assignment.

The numbers "450mV/kPa" and "0.4mV/kPa" do not tell the whole story. The 450mV/kPa for the MPX5010 is inclusive the amplifier.
The internal piezo to measure the pressure could be the same for the MPX5010 and the MPX2010. Let's say that the piezo is 3% accurate. An amplifier increases the signal, but the 3% will not get better, it will get worse by the amplifier.

To measure 200Pa, you need a sensor that is made for such a low pressure to fully utilize the range of the sensor.
I dare to say that a 10kPa sensor is almost useless to measure 0...200Pa.

Some of those sensors are for 50kPa or 100kPa, you need a lot of luck to get a total accuracy less than 20%.

3

You need to research your pressure transducers , such ultra low pressure transducers are available and will cost accordingly .

Forinstance...

4

I think it was expressed a little unfortunate. We measure a difference of ~200mbar.

In the simulation we have the ambient pressure of ~101300 Pa and then 101473 Pa are measured in the wind tunnel. So we have a difference of ~173 Pa or 1,73 mbar.

So the question is, if the mentioned sensors can detect such a small difference at all.

Kind regards

5

I'm sorry, but I'm confused. Which pressure difference do you want to measure ? 200 Pa (2 mbar) or 200 mbar or 173 Pa (1.73 mbar) ?

6

DFRobot has an inexpensive 500pa differential sensor. Fermion: LWLP5000 Differential Pressure Breakout Board (±500pa) - DFRobot
Perhaps the assignment expects you to get the required accuracy by making a calibration curve which you incorporate into your Arduino code.

For the professor to assess your attempt they must already have the instrumentation to measure that pressure with that level of accuracy. Find what they are using, and use it to calibrate your sensor.

Presumably measuring tiny pressure differences requires having a high quality wind tunnel with a very uniform flow. Hopefully you have that otherwise your experiment is just going to measure imperfections in the wind tunnel, not the thing you are trying to measure.

1 Like
7

Are you trying to measure the actual pressure in the tunnel or the stagnation pressure (as in a pitot tube)? The arrangement of the sensor with respect to the airflow is critical for this

8

Hi,
I think as @MarkT has asked, how are you going to measure the differential.
Can you post a diagram of how you will sense the pressures in the tunnel.

Tom... :grinning: :+1: :coffee: :australia:

9

Hello,

I have same question, but I need to measure pressure difference in and out of a chimney. That give me a knowledge about draft inside of a chimney. Difference between in/out is about 5-25 Pa.

I bought MPX5010dp for this task.

Should I use two sensors: one to measure pressure outside and other to measure pressure inside and than calculate difference in arduino code?

What kind of pressure sensor I need?
Am I right that I need sensor with 10kPa range and accuracy 0.0001%

10

I doubt you're going to find sensors with a basic accuracy of 0.005% or better (5Pa as a proportion of 1atmosphere). That's what you need if you are comparing two sensors.

You definitely need a single, differential, pressure sensor for measuring this sort of situation.

However the reading will be useless if the outside port is outdoors on a windy day. The wind stagnation pressure will dominate.

11

So, this one should be good enough

IN and OUT - I mean, "inside" of a chimney and "outside" in the lab.

12

The SDP816-125PA will give a total inaccuracy of about 5% (including the Arduino).
Where inside the chimney ? Normally the pressure is measure at the begin and at the end of a tube.

13

I am measuring draft in about 500 mm above stoves or fireplaces.

Do you know how proffesional analyzer like WohlerA450 or other works? Thay give me draft measurement with 0.1 Pa accuracy.

14

If you mention something, then please give a link to it.

This is one of the many types of the Wöhler A 450: https://www.woehler-international.com/shop/products/measuring-instruments/flue-gas-analyzer/a-450-basic-unit.html

Resolution is not the same as accuracy. I can make a temperature sensor with a resolution of 0.01°C for 25 dollars and a accuracy of ±1°C. That means it is possible to see if the temperature rises or drops with a high resolution, but the overall accuracy is not so good.
(In case if someone is wondering how: 10 pins with 10 fake DS18B20 each, average of 10 samples)

The device in the link above has:

  • a resolution of 1Pa
  • below 40Pa a accuracy of 2Pa
  • above 40Pa a accuracy of 5%.

The 5% is with a normal pressure sensor, but it seems that they have done something special to increase the accuracy for low pressures.

I have also looked into datasheet of other A 450 devices, and they are sometimes a lot better. They must have a better pressure sensor in those devices.

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