Module operation is from a 24 Vdc ground referenced power supply. The ST-MPA24 has an internal pass transistor-regulator filter circuit which permits this incoming voltage to be adjusted to the desired phantom voltage, up to 92% of the supply input voltage. A multi-turn trimming potentiometer is provided to reduce the phantom voltage if desired. In the default fully clockwise position, the ST-MPA24 provides "P24" 24 Vdc phantom voltage conformant to IEC 61938.