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Air Compressor Testing 2001 - Technology |
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| I'm pleased to say that pneumatic pump testing has now gone high tech with the provision of a pressure sensor lovingly handcrafted by John Barnes. | |
| It came in an elegant 4x4 housing that matches the light and rotation sensors. The tube sticking out, fits the Lego pneumatic tubing perfectly. | This is the chip that's inside. Now you know what that tube thing leads to. |
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| For those who must know everything, here are the Technical Specs | |
| Here to make it complete, is the circuit diagram | |
| You can find out more about pressure sensors at the Homebrew Sensors Page by Michael Gasperi | |
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| Check out | |
| I lost no time in testing out the new pressure sensor. John had also provided a tire pressure gauge which had been modified with a nozzle to fit the Lego pneumatic tubing. So it seemed natural to do a calibration of the pressure sensor against the tire pressure gauge. In use, the pressure sensor is connected as if it were a light sensor. | |
| I used two different setups: | |
| a. RCX - after initialising the
port for a light sensor, the light values were read off as I worked a
hand pump to get various pressure readings on the tire gauge. b. Lego Engineer 2.0 - I used the Demo mode to read off the light values of the pressure sensor connected to the blue port 5, working the hand pump as before. |
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Here is the chart showing the light value readings at various pressures as shown on the tire pressure gauge: |
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| The Calibration Issue | |
| However, I hesitate to call this a calibration chart because as John pointed out, I should trust the silicon sensor more than the mechanical tire pressure gauge, which are so cheaply made. | |
| So, henceforth you will find that the pressure sensor readings will be expressed not in psi but in light values (or pressure sensor values) to emphasise the accuracy of the pressure sensor compared to the tire gauge. I guess this will take some getting used to. Till I can get hold of a more accurate reference to calibrate the pressure sensor. | |
| Air Compressor Testing with the Pressure Sensor | |
| Air compressor testing has been updated with the availability of the new pressure sensor. Here are the details of the testing procedure. | |
| Hardware | |
| I use a Lego Dacta Control Lab
Serial Interface B. The pressure sensor is connected to the blue
sensor port #5 configured as a light sensor. The motor of the air
compressor is connected to output port A. Two setups are shown. On the left, the tire pressure gauge is included for comparison with the pressure sensor values. On the right, the pressure sensor is directly connected to the compressor. It will be shown that the inclusion of the tire pressure gauge affects the readings of the pressure sensor. In effect, it imposes a load on the system under test. |
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| Software | |
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I use Lego Engineer ver 2.0. The program or vi starts up the compressor motor and thereafter a waveform chart logs the pressure sensor value. At the end of the run, a waveform graph is displayed together with the maximum pressure sensor reading. This is how the program looks like: |
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