# How to calibrate the Voltage Port

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 configuration.