MPX5700AP and other pressure sensors failling, can't get to know why

[valentinfage]

Hi all,

I've recently bought severals sensor pressure from the Freescale brand, the MPX5700AP was the most appropriate as it is a 700kpa pressure sensor. I needed it to measure the pressure in my air pneumatic circuit of maximum 45PSI. All of the sensors I had died in few hours. I can't understand why. They're all receiving 5V in Vcc in pin 3. Pin 2 is linked to ground. Pin 1 to an arduino analog pin.

Why are they dying? Is this an electrical circuit issue? If yes, what is the correct way to plug them into an electrical circuit? My V supply is limited to 5V so I don't see how they could have received over voltage or so forth. Same for Over pressure, my compressor can't go over 60PSI.

MPX5700AP are normallt 4.75V to 5.25 in full span now the Vout is  around 1V to 1.50V ish for one of them. I have no idea why they're stop functinning. Are they really sensible? Is it because I'm using pneumatic air and therfore it "can" contain humidy? Is there any electrical schematic I should use that i'm not? I'm completely lost here

Any idea on the matter would be glady appreciated

[Joshevelle]

Hello valentin,

I have used that very same sensor for a similar application and I didn't have any problems with it. When you said "died in few hours" what exactly happens to the sensor? is the output voltage zero? is the sensor hot to the touch? how much current is the sensor consuming?.

The only _recommended_ (but not required) circuitry for this sensor is shown in Figure 4, page 4 of the datasheet:

http://cache.freescale.com/files/sensors/doc/data_sheet/MPX5700.pdf

Could you please share your schematic? please include the arduino part too.

Regards,

Josh

[valentinfage]

Hey Josh,

Thanks for your answer. I can't share anything right now I'm not at the office but basically:

- Pin1 of the sensor is directly connected into the A0 arduino pin.

- Pin2 of the sensor, to the ground

- Pin3 to Vcc.

So no capacitors nor resistances are inbetweens. I can read value on my arduino serial monitor, so it does work. But after few hours it stopped. By that I mean the serial value number where totally random which meant that A0 wasn't receiving any voltage so if I unplugged the sensor or plugged it, the value were not changing (still totally random). The sensor is cold so totally normal. It just stopped working. The current is (from memory) 7.0mA.

I'm measuring Volts inbetween ground pin and Vout and it's around 1v and 1v5 when I apply pressure. It's low. The value changes so it works in a certain way but it's not 4.58V or 4.81 as it should. For the two others sensors, the Outpout voltage is 0 yes.

I wonder if peak pressure can't "break it"? My compressor delivers 45 PSI in the circuit but the tubes are of 6mm and maybe when solenoids turned HIGH, the peak of pressure that comes in the sensor is much higher than its burst limit? Would that be possible?

[Joshevelle]

Hello again Valentin.

I cannot catch any problem in your hardware, I ran a test with the very same pressure sensor connected to a pressurized tank at 100PSI, for almost a month without any problems.

I would highly recommend you to use the filter shown in figure 4, that would reduce noise measurement (if any).

You also mentioned that your compressor cannot go over 60PSI. The MPX5700 has a pressure range from 0 to 700kPa (101.05PSI). Let's say that your compressor reaches the 60PSI, that would be ~59.11% of the pressure range, which equals to an output voltage of ~2.57v.

Also, please notice that you're using the AP version (MPX5700AP) which is an absolute pressure sensor, hence you're measuring atmospheric pressure PLUS the pressure in your tank. Your application requires a gauge pressure sensor (MPX5700GP or DP), so you can measure the differential pressure between the compressor tank and the atmospheric pressure (gauge pressure type).

Please double check your measurements, 1.5v output voltage would correspond to ~27psi.

Hope it helps.

Josh