Bidirectional Mapping with Two Channels
Obtaining single-axis control by mapping two independent channels to the forward and reverse directions of one motion. The 2-channel variants of the ST100, SF100 and SF200 are designed for exactly this arrangement: CH1 drives one direction, CH2 the opposite direction, and the two are prevented from pulling in at the same time.
On an on/off relay output the direction information is held not in the contact itself but in which contactor the contact drives. CH1 pulls in the forward contactor, CH2 the reverse contactor; the motor's direction of rotation is reversed by changing the winding connection.
This arrangement has three critical rules:
- No simultaneous pull-in: if the forward and reverse contactors pull in together, a phase-to-phase short circuit occurs. Electrical interlocking (mutual NC contacts) and a mechanical interlock must be used together.
- Dead time on direction change: a short delay is left so that one direction contactor does not pull in before the other has fully released; otherwise the contacts are worn by arcing.
- Direction verification: during commissioning, confirm with no load that CH1 really gives the expected direction; reversed wiring is the most frequent commissioning error.
With the same logic the 2-channel set suits all bidirectional applications such as sliding gates, barriers and single-axis platforms; what matters is not what the motion is but that it is bidirectional.
Context in which this term is used: Wireless Crane Remote Control Selection Guide