Latching Relay Kill Switch

[GeorgerinNH]

Hi All,

Relatively new to this, so hopefully I am providing enough information.

I have a piece of equipment that has a manual kill switch that I would like to modify. Basically, I am adding two sensors to the piece of equipment. The sensors will hook up to a 7408 AND gate. When both sensors are satisfied at the same time (normal condition), nothing will happen, but when one (or both) of the sensors is not satisfied (abnormal condition), a the AND gate will send a signal to a dual coil latching relay which will open the circuit, thus shutting the system down. Right now, I plan to put the dual coil latching relay in series with the kill switch so that the system can be shut down by either the manual kill switch or the latching relay being triggered. The relay will have a manual reset button to close the latching relay and restart the system.

Does this sound reasonable? Am I missing anything important here.

Thanks for your help,
Charlie

 

[ronsimpson]

Sounds good.
What kind of sensors? There may be a way of not using the 7408. AND is simple.
What voltage of relay coil?

Latching relays may have a dominate coil. It both coils are dive what happens? If the operator rides the RESET what do you want to happen?

 

[GeorgerinNH]

Both sensors will be capacitive proximity sensors, 5VDC.
**broken link removed**

With that in mind, I think I would be looking at a 5VDC latching relay. It shouldn't matter if the operator just quickly presses the reset or holds it (that's what you mean by "ride", correct?), it should just activate the relay to close the circuit.

"Latching relays may have a dominate coil. It both coils are dive what happens?" I don't have enough knowledge to make sense of this. Explain further?

 

[alec_t]

Presumably you don't want the reset to take place if the fault condition is still present when the reset button is pressed?

 

[GeorgerinNH]

That is correct.

 

[ronsimpson]

Presumably you don't want the reset to take place if the fault condition is still present when the reset button is pressed?

May you do want the reset to be dominant. If the machine has hit the limit switches, you might need to reverse direction but the machine is in shutdown. You need to hit reverse and reset at the same time to back away for the limit switches.

OK, I don't know what machine you are using.

 

[alec_t]

There are 16 versions of the linked sensor. Which one do you have?

 

[crutschow]

I believe you want the kill switch in parallel with the sensor output, not in series.
(Just make sure that the kill switch signal doesn't damage the sensor AND gate output. A resistor or diode in series with the AND gate output may be sufficient for that purpose.)

 

[Reloadron]

Right now, I plan to put the dual coil latching relay in series with the kill switch so that the system can be shut down by either the manual kill switch or the latching relay being triggered.

I don't think you want a dual coil latching relay in this application. Currently you have a system with a "Kill Switch". A Kill Switch is generally a normally closed push button switch, on some when pushed they mechanically latch open while on others they simply create a momentary open. Kill switches also generally have a large red mushroom button making them easy for a machine operator to hit. Some machine start / stop circuits run on low voltage DC while others may run on line voltage (AC Mains). The below circuit is a very basic example of a typical latching relay circuit as used on machinery.

In the example the Kill Switch, Prox 1 and Prox 2 are all normally closed contacts allowing voltage to the Start Push Button. When SW2 is momentarily pressed RY1 pulls in. The normally open relay contacts across SW2 close and this action "Latches" RY1 in an On state. Any break in the line, be it the kill switch, prox 1 or prox 2 opening then RY1 will drop out. Pressing the start button won't do anything until the fault that caused prox 1 or prox 2 to open is resolved.

Per Alec, the switches you are looking at come in several designs as to output to drive a relay. Knowing your design is important. For example you see NPN and PNP used in the description. For example you may want an NPN Open Collector switch so each switch output can be configured to drive a NAND or AND gate.

There are 16 versions of the linked sensor. Which one do you have?

That is pretty important.

Ron

 

[alec_t]

Something like this should do what you want, if the sensors are of the NPN-N.O. type (i.e. with open-collector outputs.

 

[KeepItSimpleStupid]

You MIGHT consider a safety relay. https://ab.rockwellautomation.com/Relays-and-Timers/Safety-Relays