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.
Asked
Active
Viewed 74 times
0
-
1How about a relay that interrupts power to its own coil when de-energized? Once it's off, it can't come back on. – Jonathan S. Jul 06 '21 at 16:09
-
1When a relay's contact controls it's own coil (latching action) I've heard this called a ["seal-in" circuit](https://instrumentationtools.com/what-is-seal-in-circuit/). – rdtsc Jul 06 '21 at 17:54
1 Answers
0
"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:
Transistor
- 168,990
- 12
- 186
- 385
-
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. – John Birckhead Jul 06 '21 at 21:39