MPX5050DP sensor problem

[jimbutcher]

I am trying to use a MPX5050DP sensor.  I am using a MC7805 three terminal regulator to convert 12VDC to 5VDC.  I have connected 5VDC to pin 3 (Vcc) and ground to pin 2.  When I measure the voltage at pin 1 (Vout) with no differential pressure, I observe about 2VDC.  From the datasheet, I expect nearly 0 VDC.  When I blow into the sensor, the voltage changes only .1 or .2 VDC.  I have experienced this with two different MPX5050 and with a MPXV5050DP.  Why isn't the output 0 (or actually .2) with no differential pressure?

[reyes]

Hi Jim,

That is not a normal behavior, if you are using a differential pressure sensor (with two port as case 857C-05 or Case 1351-01 from page 2 of the datasheet) and you are not applying pressure or obstructing any of the ports, the resultant output voltage should be close to 0V.

The reason is because the output voltage of these pressure sensor is given by the differential pressure on these ports. Can you confirm that there is no pressure applied to any of the ports?

Now, I want to confirm the connections, the MPX5050DP (Unibody case 857C-05) should be connected as you properly mentioned:

*Pin 1 = Vout

Pin 2 = GND

Pin 3 = VCC (5V)

Pin4, pin 5 and pin 6 should be disconnected.

*Make sure that pin 1 is the one with the mark on the pin, like is marked as “PIN 1” in page 10 of the datasheet.

For the case of the MPXV5050DP (SOP Case 1351-01), connection should be as follow:

*Pin 1, pin 5, pin 6, pin 7 and pin 8 should be disconnected.

Pin 2 = VCC (5V)

Pin 3 = GND

Pin 4 = Vout

*Pin 1 is also marked with a little hole in the top part of the pin.

About external components, since these pressure sensors are “Integrated Pressure sensor”, there is no need of many external components, you would only need some capacitors as can be seen on Page 5 of the datasheet. Make sure that you have this capacitors in your system.

Have a great day,
Jose

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[jimbutcher]

Jose,

thanks for the reply.  I have them connected exactly as you say, pin 2 ground, pin 3 5v and pin 1 output. 

When I measure my power supply without the sensor connected, I have 5 volts.  When I connect the sensor pin 3, the voltage drops to about 1.2 volts and the output voltage is about the same, 1.2 volts.  I see this with both MPX5050DP unitbody sensors and with MPXV5050DP small outline sensor.

My power supply is a 12 volt 10 amp supply with a two resistor voltage divider giving me 5 volts.  It certainly has plenty of amps to operate the sensor (its not a voltage drop due to load).

I have used MPXV4006DP sensors and expected the MPX5050DP to operate the same way.

Jim

[jimbutcher]

Jose,

I do not have any capacitors connected.  Are they necessary?  I have not used them with other MPX sensors.

[reyes]

Hi Jim,

It is recommended to have the capacitors connected, we use these capacitor as decoupling capacitors to avoid noise in the signal, but for test purposes on this case we can leave them unconnected.

MPXV5050DP should typically operate in the same way as the MPXV4006DP, the only difference between these devices is the pressure range (0 to 6kPa for the MPXV4006DP and 0 to 50kPa for the MPXV5050DP).

The behavior you are seen with the voltage drop on the MPX5050DP is not normal, there should not be a voltage drop. Are you testing the pressure sensor by itself or do you have something else connected?

Unfortunately, at this moment I do not have any MPX5050 pressure sensor, but I just performed test on a MPX5010DP (10kPa range), a MPX5100DP (100kPa range) and on a MPX5700DP (700kPa range) from the same family and I cannot reproduce the issue you are seen. I not using the external capacitors for these tests and everything seems to be working properly. On all three devices I’m getting between 0.1V and 0.2V without any voltage applied, and when I blow into port P1 using a hose I can get up to…

5V on the MPX5010DP (saturated at 10 kPa of pressure),

about 0.9V on the MPX5100DP (at about 12 kPa of Pressure),

and about 0.28V on the MPX5700DP (close to the 10 kPa range of pressure).

One more question, is your pressure sensor soldered to a PCB or you are testing it by connecting it directly or using a protoboard/breadboard?

I just want to make sure that the pressure sensor did not suffer any damage when solder it to the board if this is the case.

Have a great day,
Jose

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[jimbutcher]

Jose,

I am testing the sensor by itself - just sitting on the table.  The sensor has wires solder to the pins.

I think I will purchase another sensor from a different supplier in case these are all bad for some reason.  I will test the new sensor without solder.

I will let you know what I find out.

Thanks,  Jim

[jimbutcher]

Jose,

I tested another MPX5050DP today.  This one I purchased from a different supplier.  I did this in case the first supplier had sensors that were defective.  But the one I got today operates exactly like the others.

I apply 5 vdc to pin 3 and ground to pin 2. I measure the output on pin 1.  I measure the 5 vdc before connecting to pin 3 and it is 5 vdc.  When I connect it, the voltage drops to about 3 vdc and pin 1 reads the same voltage. All three MPX5050DP I have do the same thing. 

Is it possible that the pins are marked wrong?  Could the pin with the notch actually be pin 6? 

Could you test with a MPX5050DP at your lab?

Thank you.  Jim

[reyes]

Hi Jim,

This is a very strange behavior, I'm requesting some samples of the MPX5050DP to test them in our lab, meanwhile, can you please send me some pictures of your "failing" devices to check the complete part marking and confirm with the fabric if there is a known issue, please?

Also, if you can send me a picture of the HW setup of your test to replicate it on my tests would be useful.

Regards,

Jose

[jimbutcher]

Jose

Here are some photos.

I now have three sensors.  Two were purchased from Digikey and the  case says MPX5050DP KGJ1618A.  The other was purchased from Newark Electronics and the case says MPS5050DP KGK1622A.

Below are photos of 1, all three sensors, voltmeter showing 5 vdc from 3 terminal regulator, volts on pin 3 when 5 vdc connected to pin 3, and volts on pin 1 with 5vdc on pin 3.  Note that volts on pin 1 varies up and down at least .1 volt

Photos:

[reyes]

Hello Jim,

Thank you for share the details with me, I'm doing a little more research with the product engineers meanwhile the samples arrive.

One other request, Can you test your pressure sensors using a different power supply?

Thanks,

Jose

[jimbutcher]

Jose.

I have tried this using a 12 volt power supply and a three terminal regulator to convert to 5 vdc.  I also tried using the same power supply and two resistors in a voltage divider.  I also tried the three terminal regulator and a 12 volt battery.  Same result.

Jim

[reyes · Accepted solution]

Hi Jim,

I received my samples of the MPX5050DP and the MP3V5050DP and I have just tested them and they work as expected:

MPX5050DP:

Vin = 5V on pin 3

GND on pin 2

Vout closed to 0V without any pressure applied.

And the output properly change when pressure is applied to port 1:

And with the MP3V5050DP I get very similar results but using VIN at 3.0V.

I have strong reasons to believe that the devices that you are receiving have a quality issue, I recommend you to contact your distributor directly and ask them to create a CQI Quality ticket with NXP.

Have a great day,
Jose

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[jimbutcher]

Jose,

Thank you for the update.  What is the number on the one's you tested?  Mine are KGJ1618A and KGK1622A.

Jim Butcher

[reyes]

Hi Jim,

Sure, numbers on the pressure sensors that I tested are:

MPX5050DP: K1207AD

MP3V5050DP: KAP522A

Have a great day,
Jose

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[jimbutcher]

Jose,

I just checked both sensors and each draws 1.36 ma.

Jim

[reyes]

Hi Jim,

Just adding something:

When I say that without any pressure applied the resultant voltage should be “close to 0V”, I mean that it can be around the zero pressure offset value, for the MPX5050DP, this means that it could be between 0.088V and 0.313V without any pressure applied.

This offset can be eliminated applying a pressure calibration with your mcu, this is explained in the application note AN1636.

Have a great day,
Jose

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