he PDA20-PD 4-20 mA analog signal generator is what creates the 4-20 mA signal that controls what is shown on the meter display.
The signal generator come prewired to the ProtEX meter and only needs to be plugged into a wall outlet in order to function.
When powered, simply turn the knob to the left or right to increase or decrease the amperage.
This simulates the 4-20 mA analog output that a level transmitter or flow meter would output to the ProtEX meter in a real world application.