Simple E-stop string

[MartyMan]

Does anyone know of a circuit or device that would let me have a simple series e-stop string (using one N.C. contact per e-stop only) and still get individual status of each switch?

 

[nornrich]

MartyMan,

You could pull a connection off of either side each of your e-stops and run that through an LED back to your supply to indicate switch status.

Regards,

Rich...

Richard Nornhold, PE

http://www.ovenind.com

 

[itsmoked]

There is something for that.. Perhaps resistors that shunt each switch. So when the switch opens the line resistance shows which switch is open.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[nornrich]

I have also seen estop switches that have a set of NC contacts for the estop and NO contacts for feedback into your control system.

Regards,

Rich......

Richard Nornhold, PE

http://www.ovenind.com

 

[roydm]

I think you will be hard pushed to get indication with just a N/C contact unless you can bring all the contacts back to a central point. I have used a resistor chain on a overland conveyor, but you need a N/O contact for that.
Roy

 

[itsmoked]

Why not? Whichever one opens presents the resistance to be measured. It would take a bit of fussing and a calibration but it should do the trick.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[roydm]

Keith,
Yes I guess that might work, assuming you had an E-stop relay.
When you push an e-stop the relays N/O contact disconnects the coil from the circuit and its N/C contact then connects an Ohmmeter to measure the loop resistance. You would just have to be careful that the resistors were high enough in value so as not to hold the e-stop coil in.
Of course you would need a pushbutton or something to reset the E-stop relay
I think it would be easier to do with a low Voltage DC rather than AC.
I wonder if there is something in the code that would preclude you from doing it?
Regards
Roy

 

[toybuilder]

If you use binary resistor values, say 1K 2K 3.9K 8.1K, etc, you can then have a resistor ladder with a 1K resistor in series with your estop chain (with a resistor across each estop switch), and then use a DAC to measure the voltage, and a comparator to directly feed the e-stop state to your system.

Use a ratiometric voltage reference for your DAC and the trip point for the comparator. Maybe add a small decoupling capacitor to smooth out the inputs a little.