Hi Panchal,
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,
Jose
