Alps Alpine also supplies air (atmospheric) pressure sensors that are waterproof. A single waterproof pressure sensor can be used to measure both air pressure and water pressure. Here we explain the difference between air and water pressure and introduce the sensor varieties that Alps Alpine has to offer along with their waterproof structures.

Water Depth and Water Pressure

In the same way that air pressure changes with the weight of the air, water pressure (underwater) changes with the weight of the water. As water is heavier than air, water pressure rises quicker than air pressure. Water pressure also includes the air pressure portion from the weight of the air above. The diagram below shows the relationships between altitude and air (atmospheric) pressure and between water depth and water pressure.

Air weighs about 1.29 grams per liter. Water weighs 1,000 grams per liter.
The ratio between them is therefore roughly 1.29:1000, water being approximately 775 times heavier than air.
The change in pressure with a 1-centimeter change in water depth is roughly the same as for a 7.75-meter change in altitude above sea level.

Relationship Between Water Depth and Pressure

Alps Alpine's HSPPAD148A Pressure Sensor has an output range of 30-3200kPa, corresponding to between around 9000 meters above sea level down to around 300 meters underwater.

Alps Alpine Air Pressure Sensor Lineup

Alps Alpine supplies the following types of air pressure sensor, varying according to such specifications as whether or not they are waterproof, the mounting method and the measurement range.

Type	Normal environment (not waterproof)	Waterproof
Part number	HSPPAR003D	HSPPAD132A	HSPPAD143C	HSPPAD147A	HSPPAD148A
Mounting	Surface mount	FPC	Surface mount
Output(I/F)	Analog	Digital(I2C)	Digital(I2C)
Pressure measurement range	500 to 1100hPa	300 to 1100hPa	300 to 2000hPa	30 to 750kPa	30 to 3200kPa

Waterproof Structure of Alps Alpine Air Pressure Sensors

Here we look at the waterproof structures of waterproof air pressure sensors listed above. Pots of both sensors are filled with a gel that has waterproof functionality and accurately conveys pressure. This potting gel makes waterproof pressure sensing possible. The waterproof structure is complete with a ring seal maintaining airtightness between casing/lid and enclosure.

HSPPAD132A / HSPPAD143C / HSPPAD147A / HSPPAD148A achieve IPx8^*-level water resistance.
*Protection rating defined by the International Electrotechnical Commission (IEC). An IPx8 rating means there is no ingress of water even when operated while immersed in water.
This rating applies if the customer's enclosure is designed to meet IPx8 criteria after integrating the Alps Alpine pressure sensor.