Conncerning sensors MPX5010, MPX5050, MPX5100: Disintegtration pressure

[alexandersteing]

Conncerning sensors MPX5010, MPX5050, MPX5100: If I connect for a test the two sensor inputs together, the electric output of the sensor should be zero. What is the maximum pressure that can be applied to this common input against surrounding pressure before the sensor disintegrates? In the data sheet I have only found the maximum dipperential pressure.

Can I connect the inputs to water? If not, what would be an alternative sensor?

[diegoadrian]

Hi Alexander,

In general, our pressure sensors were designed and are warranted for use in clean dry air only. Our media compatibility disclaimer suggests that our customers are responsible for determining media compatibility in other environments. Customers are urged to conduct their own in-house evaluations and characterizations to determine if our devices are suitable for use in their non-clean dry air environment.

We offer a couple of application notes that give some ideas for using the devices in liquid environments:

+ AN1516 is posted at this URL and discusses liquid level control: http://www.freescale.com/files/sensors/doc/app_note/AN1516.pdf

+ AN1950 is posted at this URL and discusses water level monitoring: http://www.freescale.com/files/sensors/doc/app_note/AN1950.pdf

The gel coating on the die should not come in contact with moisture as when wet, the gel can swell and cause unreliable readings. The gel must remain intact as it protects the active surface of the die and wire bonds from oxidation.

Some customers use the P2 side and pull a vacuum rather than apply a positive pressure to P1 when interfacing with non-clear dry air. The P2 does not include the gel and so some of the media concerns are diminished, however not eliminated. Another technique used by some customers is placing a silicone grease fill over the P1 surface to protect the die and gel coat. A physical barrier can also be placed between the sensor and the media as to isolate the sensor.

The grease fill is done under vacuum to avoid air bubbles. Usually, an offset calibration is necessary because the grease creates some mechanical stress that may shift the offset value.

We can suggest Gelest as a supplier for the silicone grease:

Gelest, Inc.

11 East Steel Road

Morrisville, PA 19067

(215)5 47-1015

http://www.gelest.com

Again, use of the device in any non-clean dry air environment will result in the warranty being voided.

The same is true when modifying a device by adding silicone grease.

Media Compatibility Disclaimer:

"Freescale has tested media tolerant sensor devices in selected solutions or environments and test results are based on particular conditions and procedures selected by Freescale. Customers are advised that the results may vary for actual service conditions. Customers are cautioned that they are responsible to determine the media compatibility of sensor devices in their applications and the foreseeable use and misuses of their applications."

Regards,

Diego.

[diegoadrian]

Hello Alexander,

The maximum amount of pressure that the sensors could afford depends on the sensor that you are using. The MPX5010 has a maximum pressure rate from 40 Kpa, the MPX5050 has a maximum pressure rate from 200 Kpa and the MPX5100 has a maximum pressure rate from 400 Kpa. But P1 needs to be higher or equal that P2, because the P2 input doesn't have protection gel.

Moreover, for all NXP standard pressure sensor products, any environment other than dry air, will have some impact on the reliability and lifetime of the product. NXP’s silicon pressure sensors are NOT compatible with oil, gas, petrol and water or water vapors, or chemicals. 

For the use of pressure sensors in any other environments than dry air will require additional precautions and protection of the sensing element inside the pressure sensor:

In this case, I would like to recommend possible solutions to use our sensors in applications with other media than dry air:
 
1. In this case, you may protect the sensor against entering humidity or condense water by using proper silicon oil.
NXP uses two different types of gels, in order to isolate the die from the environment. The Fluorosilicone Gel (Type FE-53) and The Media Resistant Gel (Sifel). The Media Resistant Gel is used for our pressure sensors that are used in high temperature environments, mainly in automotive applications.

2. Usually in a water measurement application, a head tube is used. This is simply a piece of tubing between the sensor and the container in which the water level or pressure needs to be measured. Air is trapped in the tube and this isolates the sensor from the liquid water.

I would like refer to the following application note that would be worth to be considered in addition to the provided information.
AN3728 - Media Compatibility for IPS PRT Pressure Sensors
http://www.nxp.com/files/sensors/doc/app_note/AN3728.pdf  

I hope this information can be helpful.

Have a great day.

[alexandersteing]

Thank you very much for this clarification. I understood, that the sensor can be damaged if the above mentioned Limit is exeeded.

It might be another value before the sensor disintegrates and starts to leak.

Can you please specify this value?

Thank you in advance

Alexander