How to calibrate the Voltage Port

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For board series RPICT7V1 RICT4V3 RPICT3V1 and EmonWRT the voltage should be calibrated against the AC/AC adaptor used. We will explain how to calculate this value here.

Equipment needed

  • Any ac voltage measuring device (multimeter, scope).
  • Raspberrypi
  • The board to test must be operational.

Steps

Step 1

Setup in configuration an approximate value for VCAL. You might just use the default provided to start with. We will use VCAL = 545.0 in our example.

This can be anything but should be relatively close to the expected final value.

Step 2

Connect the ac/ac adaptor to the board to be tested and note the reading of the measured voltage given by the RPICT. Let's say in our case Vmes = 269.5

Step 3

Use the multimeter to read the real voltage value. In our case Vreal = 245.6

Step 4

Calculate the new VCAL as such 

newVCAL = VCAL*Vreal/Vmes

For us here this is newVCAL = 525*245.6/269.5 = 478.44

Step 5

Enter the newVCAL value in the adequate configuration or sketch to upload.

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