I asked Dr. Nitin Patil (founder and CEO of Mindsensors) if it would be possible to release a NXT-G block for the Mindsensors pressure sensor which calculate a pressure value in mBar instead of PSI. In many countries in Europe we use Bar and mBar to calculate pressure. In the US and Great Britain, from what I understand, PSI is usually used to calculate pressure.
note: PSI means pounds per square inch.
1 Bar = 100 kPa (kilopascals) = 1,000,000 dynes per square centimeter (baryes)
1 Bar (1000 mBar) = 14.5038 PSI
1 PSI = 0.068947mBar
(for more info look at http://www.convertworld.com/en/pressure)
The new NXT-G pressure block is more accurate.
The original Mindsensor pressure NXT-G block calculate the value in PSI. The range of the pressure level goes from 0 to 35. I knew from the characteristics of the sensor that it could be more accurate then that: The raw value of the sensor goes from 130 to 1023. That is about 25 times more accurate!
Dr. Nitin Patil did reply immediate. He would try to fore fill my request. Within 24 for hours he did send me an other email with a new NXT-G pressure block. Great service! This is the result:
note: the language in the configuration box, showing down here, depends on the language configured in your NXT Mindstorms software.
I have imported the new block in my NXT Mindstorms software environment. It override the existing Mindsensors pressure block. (afterwards I was able to import the original block to restore the original situation).
Test the NXT-G pressure block.
I have tested the NXT-G block. The new block works well within the LEGO Mindstorms software environment. I made a simple program that displayed the raw and the mBar values in a NXT (part no: 53788) screen. I worked perfect! I did a sequense of measurements, registered the raw and mBar values, recalculated the mBar value to PSI and compared it to the chart at www.mindsensors.com. It looked just fine!
I noticed one small thing: The maximum pressure level I was able to reach was 2467 mBar. The maximum pressure level that can be set in the new NXT-G block is higher:2800!?
Notice that the piston doesn't make a full stroke (move for- and backwards to it's limits). Therefor it took 683 times before the maximum pressure level of the sensor was reached: 2467 mBar. The minimum raw value of the sensor is 130 (at 2467mBar) and the maximum raw value is 1023 (at 0 mBar).
NXT-G test program.
This simple NXT-G program was used to display and record the raw value, the pressure level in mBar and the times the pump is pressed. The program can be download here...
The data is saved in a comma separated file named pressure_test1.txt on the NXT. It can be imported into e.g. Excel to make a graphic drawing: