Help pressure sensor for water MPX5100DP

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Help pressure sensor for water MPX5100DP

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Contributor I

Hello

I have a sensor MPX5100DP, I'm using it to water pressure but I've noticed that only works for air pressure, I wonder if there is any possibility of using it to water pressure and how to do it.

Thanks for your answers.

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10 Replies

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Contributor I

Hi, pls help, i need to measure a water vapuor pressure into esterilization autoclaves, pressure up to 200 KPA.

I just wonder if any MPX xx sensor can be suitable for this, regarding the hot air vapour water saturated (up to 134C)...

I ve read the app notes posted here, but they claim about corrosive gases, water vapour can be an issue?

thanks for your help

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NXP TechSupport
NXP TechSupport

Jonathan,

It is possible to use the MPX5100DP for your application, but please consider the following information.

We do not recommend all our sensor to become in direct contact with any kind of liquid substance or corrosive gases which would damage the gel and cause the sensor to become out of specification.

The strain gauge and the electronic circuitry for calibration and compensation are protected by a nitride layer but the aluminum bonding pads which provide electrical connections between the leadframe and the gauge are not protected, in order to make the bonding feasible. The complete die is also protected with a silicone gel. This gel is not fully hermetic, although we use much better gel for our newer types of pressure sensors, water or any other fluid can penetrate the gel and can reach the die. When the sensor die is in contact with water e.g., oxydoreduction reactions between Al/Al3+ and water start as soon as the sensor is biased. After some working hours, or maybe days, the aluminum pad of the supply pin is definitely destroyed, so that an open circuit on the Vcc pin occurs. This is an aluminum corrosion phenomena. But the corrosion phenomena is stopped when the sensor supply voltage is switched off. There are also some other failure causes like galvanic corrosion, but the Mean Time To Failure (MTTF) due to these other causes much longer than the MTTF caused by electrocorrosion of the Vcc pad. Therefore electrocorrosion is the major failure cause, and they are permanent.

However, as you may know, our products are used in washing machine applications, which would expose the gel to a humid environment. In these applications, the device is located at the top of a measurement tube - so water level is indirectly measured through the water pushing a trapped air column up to the sensor. As you can see in the following application notes, the sensor does not have a direct contact with water, but is separated by the air column.

AN1950: Water Level Monitoring

http://www.freescale.com/files/sensors/doc/app_note/AN1950.pdf

AN1516: Liquid Level Control Using a Pressure Sensor

http://www.freescale.com/files/sensors/doc/app_note/AN1516.pdf

We have also an application note about media compatibility:                                                       

AN3728: Media Compatibility for IPS PRT Pressure Sensors

http://www.freescale.com/files/sensors/doc/app_note/AN3728.pdf


Regards,

Tomas

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Contributor II

Dear Tomas,

This is great information you are telling us, Thank you!

I have read all the documents you have listed in the previous post. In the waterlevel application,

In figure 2 of  http://www.freescale.com/files/sensors/doc/app_note/AN3728.pdf I have noted that the pressure sensor is located at top of the pipe and it looks like it's installed upside-down where the main port is facing down.

We have the same situation as in the AN3728.pdf document. We need to measure water level by measuring its pressure and we are using MPXM2202GS sensors.

The sensor operates in room temperature and there is an air column between water and sensor and max pressure can reach 250Kpa.

I have some questions regarding this and hope to get some answers;

1) Does installing the sensor vertically upside-down (port opening facing water) increases lifetime of the sensor? what about installing it 90 degrees and connecting it via a flexible tube, would that increase the amount of condensation? and what about 180 degrees where port is facing up and again using flexible tubing?

2)which material is best suited for gluing or connecting the port nozzle of the sensor to a plastic or PVC pipe (not a flexible tube)?

3)What is the expected life time of the sensor for the above configuration/environment? I know we have voided the warranty by not using dry air but we need to be able to roughly estimate life time of the sensor...can we expect 2 years of reliable operation in this situation?

4)Does adding silicon grease increases the lifetime of the sensor giving the situation above? if Yes then which type/make of grease can we use?

5)Does Shutting down the sensor as much as possible increases its lifetime?

Many thanks and I hope my questions are not too long/much.

Best regards ,

Mike Drebby

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Senior Contributor I

Hello Mike,

Thanks for using our community. Find my answers below:

1)  The device in the application note you read was installed upside down just for the ease of use, it doesn’t really increase the lifetime of the sensor. You could install it at 90°, but I won’t recommend you to install it at 180°, since the condensation could become in water drops that might reach the device.

2) There is dedicated PVC pipe glue but the port of the MPXM2202GS is made of Polyphenylene Sulfide (PPS) and other glass compounds. So the PCV glue might not join the sensor to the pipe very well.

Why do you need to use a PCV pipe? Instead using glue, I would recommend you to use a single flexible tube going from the port of the sensor to the bottom of the water tank. Looking at the image you mentioned (AN3728,  figure 2), I would do a small modification:  the air column should go from the sensor to the bottom of the flexible tube, not at the same level of the water or higher as shown in the image. This air column inside the flexible tube would be naturally crated, just connect the sensor to the tube and hold the tube at the bottom of the tank with something heavy, like a metal washer hold it to the tube with a pin (please take a look at the attached image).

3) Unfortunately it is impossible for us to estimate a life time. However, the main contributor for a sensor failure in this kind of applications is the offset (it increases over time), so I would recommend you to use “Autozero”, a software technique that basically reads the offset of the pressure sensor and compensates the sensor’s measurements to increase accuracy, regardless of the offset level of each specific sensor.

Auto-Zero:

http://cache.freescale.com/files/sensors/doc/app_note/AN1636.pdf

4) Absolutely, if you protect the sensor with extra grease you would increase the lifetime of the sensor, however I would still recommend you to use Autozero (because of the offset). We would recommend Parker O-lube silicone grease or DMS-T46 or T51. Basic recommendation is to use silicone oil (or preferably grease) with high viscosity and high molecular weight. In this case the size of the molecules are big enough to limit the penetration of the grease inside our protective silicone gel which is over the die. In terms of contaminants, the silicon grease must be free of halogenures (Cl content < 50 ppm) to reduce the risk of bond pad corrosion. On the other hand, don't forget that whatever the material you will use, as soon as you put something on our gel you have a high probability to see some offset drift.

We can suggest Gelest, Inc. in the United States:

Gelest, Inc.

11 East Steel Road

Morrisville, PA19067

(215)547-1015

http://www.gelest.com/

Alternatively, you can contact Shin-Etsu Chemical Co., Ltd. in Japan.

Their URL is: http://www.sifel.jp

5) Most of our quality and reliability tests for pressure sensors are done with biased sensors. So the information we have regarding non biased devices is for storage only: temperature cycling, mechanical shock and vibration. However, we have an “Accelerated Life Testing” (biased), where we estimated a cumulative device hours of 1,242,172 at customer’s use condition.

So theoretically speaking, it is possible to extend the device life time if is not turned on, but there is no solid information to backup this.

For detailed information please take a look at section 1-9 of our data book DL200/D :

http://cache.freescale.com/files/sensors/doc/data_lib/DL200.pdf

Please note that the size of the book will require ~25MB.

I hope you find this information useful, please let me know if I can help any further.

Have fun!

Josh

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Contributor II

Josh,

This is more than a wonderful answer. I got much more answers than I was hoping for, a huge thank you for this effort.

2) Actually I mentioned PVC by mistake, I was planning to make the sensor port face and connected directly to the plastic package which will include a hole/pipe. I was hoping to minimize the number of junctions and parts by doing this. So I am planning to glue the sensor port directly to the plastic package. I am not sure which plastic is best but it must be of a good grade.

The device (which contains the sensor) will be installed below the water tank and no the other way, see attachment please. There will be some air between water and sensor (see the white gap below the sensor).

00.png

4) This is great info that I did not know and yet indeed very easy to implement. One question; actually two :smileyhappy:

     -Is the drift always in one direction and towards the high end of the sensor?

     -Does adding grease or oil you have mentioned above, will add some drift? or drift only increases due to aging?

Again Josh, many thanks for the great info you have supplied.

Regards,

Mike

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Senior Contributor I

Mike,

You’re very welcome.

2) I wouldn't recommend you to install the sensor as shown in your attachment, that installation implies an extra drill in the water tank to insert the pipe; also, almost the entire pipe would be full filled with water, instead of air (as we recommend), that would cause high humidity and moisture forming into the sensor. Another problem would be that, in order for you to calibrate the sensor you must empty the tank and unplug the sensor from the pipe.

I would highly recommend you to try the suggestion I sent. You would only need a flexible hose and a couple of metal washers. I've used PARKER PARFLEX SERIES U:

Parker - SERIES U:

http://tinyurl.com/parflex

You could also connect the sensor to the “device” with flat wire (four wires to be exact: GND, VCC, V+ and V-), so you can still have the “device” installed below the water tank.

4) Sorry, but I didn't understand the “drift direction” question. The extra grease brings some mechanical stress that might shift the offset value. Please notice that adding any kind of material to the pressure sensor will lead to offset drift, so you would need to calibrate the sensor once is filled with extra grease.

Please correct me if I misunderstood your question.

Hope it helps,

Josh

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Contributor II

Hi Josh,

2) I don't have access to the tank, only to the pipe. Also as far as I know, it does not matter how much air between the sensor and the water because eventually the air will be 100% saturated. So in other words; it does not matter how much air there is, as long as there is some.

4) What I meant by "drift direction" is that the drift will always increases with time, so if after one year the drift is x, then after two year will be always more than x, so it does not fluctuate.

Regarding the grease; should I create vacuum inside the sensor to fill it or is there easier way? or maybe easy way to create vacuum...

And how important is it to get the grease type you recommended? I don't have easy access to it. If I search a web-store , like Amazon for "silicon grease" I can see it has been categorized in the following:

-for o-ring

-for automotive/dielectric

-lubricant

-plumbing

-under water housing/diving equipment

Can I use one of these?

Best regards,

Mike.

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Senior Contributor I

Hello Mike,

DO NOT apply vacuum into port after filling it with silicon, that would damage the sensor since P2 would be greater than P1, expose the whole package to vacuum to remove any remaining bubbles. The best process would be to expose the package to vacuum while adding the silicon, however I would recommend you to run some tests without vacuum, you could use a syringe and remove the air from the silicon before adding it to the sensor that would be enough.


Any silicon with with high viscosity and high molecular weigh would do the trick :smileywink:. I did a quick search on Amazon too and I found "Novagard G661 General Purpose Lubricating, Protecting and Dielectric Silicone Compound" which features:


"non-toxic, odorless, non-corrosive, non-melting, chemical and water resistant, and a wide service temperature range of -40ºF to 400ºF"


I've never use it before but _for me_ it looked like a good option.


Have fun!

Josh



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Contributor II

Great!

Thanks Josh.

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Contributor II

Hi All,

I am having too many sensors failing, its MPXM2202GS, about 30% within 2 months after installation.

1) Using 5vdc as power supply

2)Using pulsing, so the sensor is only On for 10% of the operating time

3)I used/tried to insert silicone oil by putting the sensors in vacuum to remove the air and replace it with silicone oil

4)Sensors were installed up-side-down as showed in the previous figure

5)There is an air column between sensors and water, so basically we followed the advice in "AN3728, Media Compatibility for IPS PRT Pressure Sensors"

6)Temperature is between 10 and 30 Celsius and all devices installed inside, so no harsh environment

7)The applied pressure is within the range of the sensor (0 to 200Kpa)

8)I noted that the silicone oil got out of the sensor port when installing the sensor up side down.

When I tested the failed sensors the resistance between Out+ and Out- where infinity while its about 2K2 ohms on a good/new sensor.

So what have we done wrong here?

Was the idea of inserting silicone oil not a good one?

Is it possible that putting the sensor in vacuum has affected the gel layer of the sensor?

Is it possible that silicone oil affects the gel layer?

Was it better if we did not try to put silicone oil at all?

any idea how to improve life of the sensor or solve the problem of the failing sensors?


Best regards,

Mike.


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