# MPXV7002DP pressure sensor expanded pressure range

Hello all,

I'm new to analog sensors and trying to get some clarification on how to use this sensor, MPXV7002DP. The sensor is rated from -2kpa to 2kpa, but several of the sellers comment that

"with an offset specifically at 2.5V instead of the conventional 0V, this new series allows to measure pressure up to 7kPa through each port for pressure sensing but also for vacuum sensing (refer to the transfer function in the data sheet for more detailed information)".

I'm trying to figure out what this means and how to actually use this to measure up to 7kpa. Everything I've searched just gives the exact same wording without any further explanation. I checked the data sheet and the transfer function is Vout = VS × (0.2 × P(kPa)+0.5) but I don't see any other info.

Does this mean that rather than attaching the sensor to ground and +5v, I should attach it to +2.5v and +5v? Or do I move the high rail up as well so I input +2.5v and 7.5v?

Or do I wire it as usual and just alter the transfer function?

Or am I just misunderstanding the information and this isn't something I have to change, but that I can just use it normally up to a higher pressure than rated...

Thanks in advance for any assistance

Forget about voltage when using this sensor. You're not using/building a voltmeter.

Sensors like this are ratiometric, meaning that they output a ratio of their supply.
Only if you power them with 5.000volt, they will output 2.5volt, but when is that going to happen.

The datasheet should simply state that they output half of their supply without differential pressure (the 'D' type), and 10% or 90% of their supply with -2kPa or +2kPa differential pressure.

Fortunately most Arduinos have ratiometric A/Ds.
The A/D outputs ~512, whatever voltage you supply to the sensor (within reason) without pressure.

The code should get the A/D value from the analogue pin, subtract ~512 from it (the offset),
and multiply the result with a factor to display in kPa, bar, psi or whatever.
Leo..

Thanks for your reply. I think I have a basic understanding of how these work, the part I'm stuck on is the vendors note (quoted in my first post) about using the sensor up to 7kpa. This sensor is rated to 2kpa, but all the vendors have notes about measuring up to 7kpa. This is what I'm trying to figure out how to do.
When I look at the data sheet I don't see any mention of this or details on how to do it. In the example you gave, you said that it might output 10% and 90% at -2kpa and 2kpa, which is consistent with the data sheet. But if this is the case, how do I measure up to 7kpa. The transfer function is Vout = VS × (0.2 × P(kPa)+0.5). Assuming 5v input, the output at 2kpa is 4.5v, which fits with what you said. However, the output at 7kpa would be 9.5v, which obviously isn't possible since it's nearly double the input. What am I missing?

"with an offset specifically at 2.5V instead of the conventional 0V"

This could already be wrong. Never seen a pressure sensor with a 0-5volt output that starts at 0volt.
Some (gauge) sensors start at 10% (or 5%).
For now I would say this Amazon/ebay statement is wrong, until proven otherwise, and the datasheet is correct.

Stop assuming 5volt. Assumption is the mother...
Only "50% idle" and "10-90% span" of the A/D range is correct.

float pressure = (analogRead(A0) - 512) * 0.00489; // in kPa
Leo..

@Wawa, you are too gentle. Let’s say it how it is.

This is 100% pure nonsense:

“with an offset specifically at 2.5V instead of the conventional 0V, this new series allows to measure pressure up to 7kPa through each port for pressure sensing but also for vacuum sensing (refer to the transfer function in the data sheet for more detailed information)”.

Then why would sellers write that ? Because they are stupid and they don’t care. That’s why.

Someone copied that text from a 7kPa sensor, and the rest copied it from there.

Cemtes, if you want to measure -7kPa to +7kPa, then you should buy an other sensor.
The information that you need is in the datasheet.
This is the manufacturer’s page: -2 to 2kPa, Vacuum Pressure Sensor | NXP Semiconductors.
It is a nice sensor, it works at 5V (4.75V to 5.25V) and it is calibrated to have about 2.5V output (although that might change a little) with no pressure and the output is from typically 0.5 to 4.5V when powered with 5.0V. Because it is ratiometric it works very well with an Arduino.

I can answer a few of your questions.

Does this mean that rather than attaching the sensor to ground and +5v, I should attach it to +2.5v and +5v? Or do I move the high rail up as well so I input +2.5v and 7.5v?

No, you power the sensor with 5.0 volts. With 5.0 volts applied and both ports at atmosphere the Vout will be 2.5 volts just meaning that it has an offset and that is intentional. Take a look at this figure from the data sheet.

The transfer function is pretty clear:
Transfer Function:
Vout = VS × (0.2 × P(kPa)+0.5) ± 6.25% VFSS
VS = 5.0 Vdc
TA = 10 to 60°C

The data sheet is pretty specific about the sensor limits as in -2 kPa to 2 kPa and like you I have no idea how any of that could be derived, not to 7 kPa on either port. The total span is 4 kPa and that ranges from 0.5 volt to 4.5 volts for a sensitivity of 1 volt / kPa with a Vcc = 5 volts. The merit of the offset is simple. It's also pretty common in the sensor world. Here is a similar chart but looking at current rather than pressure.

The idea behind this it makes it easy to scale your A/D code for whatever units or engineering units of measure. Since using a 10 bit A/D like the Arduino and with a 5 volt A/D reference 0 to 5 volts = 0 to 1023 bits or 1024 quantization levels. So with 2.5 volts in you get about 512 bits which is zero units on either of the above charts. Makes for easy measure of negative units having the positive offset. Can't put a negative voltage with respect to ground into an Arduino.

As to the 7 kPa about all I can figure is that if I apply a vacuum of 2 kPs to P2 (Port 2) that will give me an output of about 0.5 volt with Vcc = 5 volts. Now if I apply 4 kPa to P1 ( port 1) my output voltage will go to 4.5 volts and I can't really say -2 + 4 = 6 can I. They make it sound like I can apply a vacuum of -2.5 and get down to zero volts out and then apply 2.5 kPa and end up with 7?

While I see a logical transfer function which they apparently reference I can see no way to get a viable 7 kPa in any of this? If you need to go that high I would be looking for a +/- 10 kPa sensor and unless you need delta just a single port sensor. The data sheet is pretty clear as to the limits of the sensor.

Ron

Thank you to everyone for your thorough responses. It seems that the 7kPa range listed by the vendors is nonsense, which makes me feel better about not being able to understand it.