Principle of a Sequencer

More complex sequence control can be implemented most easily using a so-called sequencer. This enables the control circuit to be designed for more than two elements (e.g. cylinders) in systematic fashion, which is therefore less susceptible to error. Sequencer control has become standard in industry.

The graphic below shows a section of a sequencer control, that has three sequences.


The following design rules apply to a sequencer:

Every operating step (sequence) has to involve latching.
A following step is only able to proceed when it certain that the previous step has been successfully completed (ensured in the above, for example, by having K1 in sequences 1 and 3, highlighted in green).
Every limit for a working element needs to be detected by a signalling element (buttons S1, S2 and S3 in the above)
Once a step is completed, the circuit that was previously active is reopened. This prevents signals being superimposed (ensured in the above, for example, by having K3 in sequences 3 and 5, highlighted in blue).
The first step of a sequence is usually handled bymeans of a separate circuit (circuit 7 and switch S4 above).

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