Air Pressure Sensor for NXT
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Limited Stock   NAP    Air Pressure Sensor    $39.00       

The Air Pressure Sensor lets your robot know how much pressure is in it's pneumatic system.

The Lego Pneumatic system uses air pressure in cylinders to create movement.  The amount of force generated by an air piston is proportional to the air pressure, and the size of the cylinder.  The Techno-stuff air pressure sensor lets your RCX measure the air pressure, and therefore know how much force is being applied to the piston.  This sensor measures air pressure in the range of 0 to 170 KiloPascals.  (0-25 Pounds per square inch)

Air cylinders are reversable.  You can apply force to the piston to create air pressure.  You can then measure the air pressure, and know how much force is applied to the cylinder.  This technique can be used to build a scale to measure weight.

         Air Pressure Sensor.

Pressure sensor with Lego air pump       Simple Test.

The easiest way to program the air pressure sensor is to download and import the sensor block from the techno-stuff website. The block lets you select output in either kPa or PSI and lets you set the compare point. The example below displays the air pressure and the Raw sensors value, and beeps when the pressure is over the compare value.

Air pressure sensor program in Lego RIS 1.0

If you are using a different programming language, you should program it as an active sensor in Raw mode. Air pressure in KiloPascals is calculated by the formula (1008 - x) / 3.38 where x is the raw value from the NXT. To get the air pressure in PSI use the formula (1008 - x) / 23. For example a raw value of 433 equates to 170 kPa or 25 PSI .

One PSI = 6895  Pascals  (Newton/meter2)
One  KiloPascal = 0.145 Pound per Square Inch