MDDA Relay consists of a power supply unit, a timer unit and an attracted armature auxiliary relay. Resistor and Zener diode combination of the power supply unit provides low voltage stabilised DC supply to the static timer circuit. Non-linear resistors are used in the power supply unit for surge suppression.
The timer unit consists of a timer circuit and a thumb wheel switch. The thumb wheel switch mounted on the name plate of the relay provides precise and high resolution time setting. The timer unit operates a reed relay which in turn energises an attracted armature auxiliary relay. This auxiliary relay is provided to achieve higher contact rating and flag indication, if required. MDDA can be provided either as a delay on pick up relay or as a delay on drop-off relay.
A normally open contact is used for initiating time delay on pick up relay and output element gets energised after the set time delay. In the case of delay on drop off relay, the output element is normally energised and with the normally closed initiating contact opening out, the output elements gets de-energised after the set time delay.