Question on emergency stop circuit

talldude42

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Join Date
May 2015
Location
MI
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Hello everyone. This is my first time designing a system from scratch. The system is for a rubber injection molding press. I have the PLC all put together, wired most of the programming done, and I am working on figuring out the emergency stop circuit now. My understanding is that when you hit the emergency stop button all functions of the machine will cease and cuts all power to everything except the controller and HMIs. I have 2 voltages, 24vDC which powers all inputs, and 110VAC which powers my outputs coming from the PLC.

My main question is, how are you able to have any sort of indicator telling the operator that the emergency stop has been pressed (such as stack light, alarm siren etc.) with out having some sort of output voltage going somewhere? Is it acceptable or common practice for this to be allowed? Our current machines were built with not much thought into these things and dont have any sort of indications that it has been pressed.

I currently have a pop up window on the hmi but thats it so far.
Thanks for your input and comments!
 
To indicate when a E-Stop is activated you set an alarm on the HMI to let the operator know what's going on.
In addition I like to bring an input from each device back to the PLC as well as the safety circuit. Then place an indicator on the HMI to tell the operator what device was activated
I like to do my emergency stops and interlock's first but that's just me.
But before you do the E-Stop and Interlocks you must do an assessment of the safety needs o the machine so you can plan the emergency / safety circuit's don't short cut them somebodies life is on the line it may be yours.
 
Never did the stack light for EPO, but on the HMI if you wire each EPO pushbutton you can have an alarm saying which was hit and at what time.
 
I would install a dual channel system.

Channel one: all emergency stop devices (Pushbuttons, guard switches and so on) in series to an ESR.

Channel two: each device as a PLC input for alarms.

Very common practice to use dual channels for e-stop circuits
 
My understanding is that when you hit the emergency stop button all functions of the machine will cease and cuts all power to everything except the controller and HMIs. I have 2 voltages, 24vDC which powers all inputs, and 110VAC which powers my outputs coming from the PLC.


It's not necessary to kill the input power, so you should still be able to detect which E-Stop PB was activated.
 
It's not necessary to kill the input power, so you should still be able to detect which E-Stop PB was activated.

That part I had figured out. The E-stop is set NC and will send a signal to the PLC input to a NC bit. Once button is pressed, cuts signal to PLC, closing bit in logic sending prompt on HMI to what button is pressed. But I will consider leaving the inputs on.
 
To indicate when a E-Stop is activated you set an alarm on the HMI to let the operator know what's going on.
In addition I like to bring an input from each device back to the PLC as well as the safety circuit. Then place an indicator on the HMI to tell the operator what device was activated
I like to do my emergency stops and interlock's first but that's just me.
But before you do the E-Stop and Interlocks you must do an assessment of the safety needs o the machine so you can plan the emergency / safety circuit's don't short cut them somebodies life is on the line it may be yours.

Yep I agree about the assessment and that is all set.
 
Aux power - stays on, for lamps, inputs, HMI's, PLC's, etc
Control power - shuts off. For anything with motion or destructive outputs.

Sometimes it is also referred to as Sensor and Actuator power on remote I/O.
 
If I specify the Emergency devices I always select lighted 2 channel E-Stop buttons
Gates and other device always 2 channel while lighted is not always practical for those
With E-stop buttons I have 7 wires to each device
1 Safety channel 1 in
2 Safety channel 1 out
3 Safety channel 2 in
4 Safety channel 2 out
5 +24VDC
6 -24VDC / Common
7 Feedback to PLC input
Safety Channels are always N.C. open on activate
Feedback to PLC is always N.C. open on activate
+24 to button light is N.O. close on activate
Ah way the operator can quickly determine the problem. I once had an operator the spent over 4 hours to find and accidently activated E-Stop that nobody owned up to.
Also remember E-Stops must bring the machine to a safe condition as quickly as possible regardless if it damages the machine in the process.
There should be only 1 reset for an activated E-Stop in some cases I have specified reset only with a supervisor password or key.
Never allow the operators to use the E-Stop as a normal stop.
I was taught many years ago it’s life or limb, machines can be repaired people don’t heal so well.
This is why a proper assessment is vital in all new applications management need to be involved in the assessment. Don’t ever put safety on a second priority level it should always be first from the time get the job until the job is signed off by management.
 
I hate to be the one to break this to you, but the above circuit will not work.
The safety channels are not powered from a 24vdc supply they are pulsed monitored to insure the integrity of the circuit you can't even check with a volt meter.
For the feedback to the plc requires a solid 24 v supply
Only one feedback per button is necessary the contacts all move together
 

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