I have a problem. I have a sensor in a piece of equipment that needs to switch off that equipment if it detects a dangerous gas. The equipment must remain off until a manual reset is applied. What kind of switch/contactor does that? Is there a special name for it? It should be inherently failsafe.
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asked Jul 6, 2021 at 16:05
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1\$\begingroup\$ How about a relay that interrupts power to its own coil when de-energized? Once it's off, it can't come back on. \$\endgroup\$– Jonathan S.Commented Jul 6, 2021 at 16:09
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1\$\begingroup\$ When a relay's contact controls it's own coil (latching action) I've heard this called a "seal-in" circuit. \$\endgroup\$– rdtscCommented Jul 6, 2021 at 17:54
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1 Answer
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"Failsafe" has a variety of meanings in different industries. Presumably the sensor output in this case is configured so that the output "on" verifies that dangerous gas is not detected.
simulate this circuit – Schematic created using CircuitLab
Figure 1. Manual reset. Auto-off if OUT signal or sensor power is lost.
Depending on the risk category you may need to employ redundant circuits. Industrial machinery uses dual channel redundancy and I have explained some of the principles of operation in the posts linked below:
answered Jul 6, 2021 at 16:40
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\$\begingroup\$ Just a warning: If your dangerous gas is flammable or explosive, this approach will certainly increase the safety. But, the approach in itself won't be certifiable for operation in a hazardous area unless the design of the switch, the equipment and the sensor all meet other requirements. \$\endgroup\$ Commented Jul 6, 2021 at 21:39