Long term water level monitoring using MPxx5004

[ben_buckland]

Hi there,

I am looking to use the MPxx5004 to measure water level over a long period of time, 5 – 10 days. I have built a test rig to check the use of the pressure sensor. A silicon tube is submerged to the bottom of the reservoir with the other end of the tube connected to the sensor. The sensor is always above the water level ensuring a column of air between the reservoir and the sensor.

What I’m seeing though is a drift in the range of 0.25 – 0.35v in a 24 hour period. The drift is not only negative but appears to be cyclical as if the sensor is being effected by temperature (or some other environmental attribute). 

Any help would be appreciated.

[reyes]

Hi,

You are performing the correct method to measure water level using pressure sensor by using the silicon tube and the column of air avoiding the sensor to be in direct contact with the water.

Sources of offset errors and drift are due to device to device offset variation (trim errors), mechanical stresses (mounting stresses), shifts due to temperature and aging. Performing auto-zero will greatly reduce these error.

Auto-zero is a compensation technique based on sampling the offset of the sensor at reference pressure in order to correct the sensor output drift or variation, this technique will correct the error on zero pressure and across the complete pressure range.

Details about the autozero technique can be found in the Application note AN1636: https://www.nxp.com/docs/en/application-note/AN1636.pdf

Regards,

Jose

NXP Semiconductors

[ben_buckland]

Hi Jose, thanks so much for you response. Pleased that I have the correct method of measurement in place.

The drift that I am seeing could be in as little as 12 hours, yesterday I observed a movement of 918mV to 1,090mv in just 8 hours where the tank had no change in water level.

Thanks in advance.

Ben.