What is Sequence On – Simultaneous Off Operation on Pump Control?
Tuesday: August 27, 2019 : Alternating Relays
I want my two loads to come on one after the other, but then both loads to stay on together until the last control switch is opened.
The diagram illustrates a type of operation known as “Sequence On - Simultaneously Off (S.O.S.O.)”- the two loads are energized sequentially, but remain on together until the OFF switch is opened. This operation works best when using a DPDT Cross-Wired Alternating Relay.
In the initial OFF state, all three switches are open, the Alternating Relay is in the LOAD 1 position, and both loads are off. No action happens with the Alternating Relay or either load when the OFF switch closes.
When the LEAD Switch closes, LOAD 1 turns on. When the LAG Switch closes, LOAD 2 turns on. Both loads remain on as long as all three switches are closed. When the LAG Switch opens, LOAD 2 remains on because the OFF Switch is still closed and auxiliary contact M2 is still closed. When the LEAD Switch opens, LOAD 1 remains on because the OFF Switch is still closed and auxiliary contact M1 is still closed.
When the OFF Switch opens, both LOAD 1 and LOAD 2 are turned off simultaneously because all voltage is removed to both loads. Auxiliary contacts M1 & M2 both open. The Alternating Relay toggles to the LOAD 2 position. The entire cycle is then repeated, but with LOAD 2 energized ﬁrst followed by LOAD 1.
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