Pressure sensor for measuring water pressure

mahesh_ausroad · ‎01-31-2022

Hi

I have a requirement to have a pressure sensor to measure the water pressure up to 10m deep underwater. the sensor will be submerged and will be directly exposed to water.

I have seen previous replies to posts where it was stated that the sensors won't last if they were directly exposed to water and the reason for failure was told to be the corrosion of the electrical terminals.

for my application, I need the sensor to be underwater for only less than 3 minutes. would this condition make any of your sensors suitable for underwater pressure measurement?

I am using the pressure measurement to estimate the height of the water column.

I don't care about the accuracy of the absolute pressure. I am only going to look at the difference in pressure at the surface of the water column and at the bottom of the column.

please help me with your valuable input. if this is possible then I will be consuming a million of your devices every year.

Mahesh

mahesh_ausroad · ‎02-02-2022

Dear Jozef

thank you, for your reply.

I went through the proposed sensor datasheet. I have few more queries

1. the supply voltage is specified as 3.10v to 5.25v. our device is going to be powered by a button battery where the operating system voltage can be as low as 2.8V. The low voltage detection threshold is specified to be between 2.64V and 2.84v. does this mean that this sensor won't be suitable for our application? do you know of anyone using this sensor on a system powered by a button battery? if this is not suitable can you pls propose a different sensor for our application?

2. I couldn't figure out the relative accuracy of the sensor. this is the accuracy of the difference between two pressure measurements. this error includes the repeatability, linearity and hysteresis errors. do you know what the value is going to be?

3. it was not clear from the datasheet what material is being used for media separation gel?

In anticipation of your reply

Mahesh

JozefKozon · ‎02-03-2022

Dear Mahesh,

1. the supply voltage is specified as 3.10v to 5.25v. our device is going to be powered by a button battery where the operating system voltage can be as low as 2.8V. The low voltage detection threshold is specified to be between 2.64V and 2.84v. does this mean that this sensor won't be suitable for our application? do you know of anyone using this sensor on a system powered by a button battery? if this is not suitable can you pls propose a different sensor for our application?

[A] Unfortunately we do not have a pressure sensor with an I2C interface for the 2.8V supply voltage. Another solution would be to use MPX4250A, which has a ratiometric supply voltage. Meaning the recommended supply voltage is 5.1V, but it can be also supplied with 2.8V and the output will also decrease accordingly. The output is analog.

2. I couldn't figure out the relative accuracy of the sensor. this is the accuracy of the difference between two pressure measurements. this error includes the repeatability, linearity and hysteresis errors. do you know what the value is going to be?

[A] The accuracy is stated in Table 100 and is guaranteed by test. The accuracy for the temperature 0° C ≤ TA ≤ 85 °C is guaranteed to be no higher, than 2.3kPa and for the temperature lower, than 0° C, and higher, than 85 °C is guaranteed to be no higher, than 3.5kPa.

s

3. it was not clear from the datasheet what material is being used for media separation gel?

[A] A flourosilicone gel is used in FXPS7250D4. If the media resistant gel would be used, it would be explicitly mentioned in the datasheet. The media resistant is a better option for media other, than clean dry air. Unfortunately ordinary flourosilicone gel is used in FXPS7250D4.

With Best Regards,

Jozef

JozefKozon · ‎02-01-2022

Hi Mahesh,

unfortunately non of our pressure sensors are waterproof and direct exposure to water or even water vapors would indeed cause a corrosion of the electrical terminals leading to component failure. On top of that our IPS PRT Pressure Sensors are using a Flourosilicone or Media Resistant Gel, which is also sensitive to water. Please find an AN3728 attached. On page 3. is a Table with test results exposing the gel to different Media.

The only method we endorse fully is the utilization of a pressure sensor with clean, dry air.

I apologize for inconvenience.

With Best Regards,

Jozef

mahesh_ausroad · ‎02-01-2022

Thank you for your kind reply Josef

I went through the test report attached. the report states that there is probability for sensor to perform ok with short term exposure. the short term is defined as 24 hours. for my application the sensor will be exposed to water only for 3 minutes. this means there is a good chance the sensor would survive the exposure.

with this in consideration can you pls recommend a sensor model that i should try.

the sensor will be used to measure the water column height up to 10 meters (200kpa absolute).

other important requirements to consider are

The sensor need to be board mounted type
Sensor port will have direct exposure to water.
I2C interface for communication with a micro controller
I don’t care about the absolute accuracy
Accuracy for relative pressure change should be within 1kpa
Must be temperature compensated.
Operating voltage – 3V
Cost – low enough to be suitable for a disposable device, (sub dollar when purchased in very large volume.)
Total life expectancy since power up – 2 days
Expected duration under water – 3 minutes
Battery operated device and hence should draw very low power.
Foot print as small as possible

please help me with your recommendation.

JozefKozon · ‎02-02-2022

Hi Mahesh,

thank you for a detailed description of your requirements. Based on this, the closest ty your requirements is FXPS7250D4 Digital absolute pressure sensor, 20 to 250 kPa. Unfortunately we do not have a pressure sensor with accuracy below 1kPa for the 200kPa measuring span. Accuracy of this sensor is +/-2.3kPa.

With Best Regards,

Jozef

JozefKozon · ‎02-02-2022

Hi Mahesh,

for pricing and availability please contact an authorized distributor by your choice from your area. Please see this link for a list or our authorized distributors.

With Best Regards,

Jozef