E-Stop Circuits

[L D[AR2P#0.0]]

As shown in the link in post#15, a time delay is required for the reset function.

 

[Jieve]

Thanks for the responses.

OkiePC,
Yes exactly, this is the hardwired E-Stop circuit drawn with a ladder logic editor.
Control Power is a momentary pushbutton exactly as you described.

LD, What do you mean a time delay is required for resetting/turning back on the control power?

We have another system as I mentioned in the original post that uses safety relays and is built according to standard, so they will be exposed to this as well, but later on. I'll check out the chatter issue. Thanks for the tips!

 

[L D[AR2P#0.0]]

The link in post#15 doesn't work for me anymore - I'll post an example later.

 

[L D[AR2P#0.0]]

See page 7/8 of the following document:

http://literature.rockwellautomation.com/idc/groups/literature/documents/td/700-td556_-en-p.pdf

 

[Jieve]

LD,

So we built the E-Stop circuit the way I had it drawn in the last PDF I posted to this forum and you were absolutely right about the time delay. When we try to engage the circuit by turning on the control power, the coils K1 & K2 engage, but before the NO K1 & K2 contacts engage, the NC K1 & K2 contacts disengage at the circuit bounces rapidly back and forth. I have built in a hardware timer into the updated circuit, shown as ladder logic in the PDF attached. Of course now if the timer contacts weld shut, well we have issues.

Can someone take a look at this and give me some direction? I was hoping to have this built with one of our systems as an intro to E-Stop circuits before going into E-Stop Safety Relays with our students, but of course real life is always a bit trickier than theory. How would people have built this circuit before the days of Safety relays? If anyone could modify my circuit with something that works properly (if mine doesn't) I would be very grateful.

Thanks!

 

[Steve Etter]

Jieve - IMHO your course is out-dated and needs to be updated. I say this because it sounds like you are teaching a technique that should really not be used anymore, not in anything new or current. The reason safety relays and other safety devices exist in the first place is because of the types of issues you are fighting now. Not only were the devices themselves unreliable but effective systems are very difficult to design, too. The vast majority of hardwired E-stop circuits I have seen are simple seal-in circuits where a "Control Power ON" pushbutton energizes the circuit and the E-stop devices are used to de-energize it. I personally never use this method any more and replace it whenever a serious modification is required where one exists.

My recommendation is to teach the seal-in circuit as history only and then jump quickly into modern safety systems. The old method is good to understand but should be academic only.

Steve

 

[Jieve]

Thats exactly my intention. I'm not teaching the technique as One to use for designing estops. Im using it for them to get an approximate understanding of how estops work. Looking at an estop relay you dont see directly whats going On inside, as someone previously mentioned safety relays still baffle technicians as well the first Time they see them. Using this method its easy to understand the concept behind them first, before getting into the safety relays.

Thanks for the response. I do appreciate it, but in the interest of time i would prefer to avoid discussions about my didactic approach, and focus On the solution to the estop problem.

 

[kolyur]

The vast majority of hardwired E-stop circuits I have seen are simple seal-in circuits where a "Control Power ON" pushbutton energizes the circuit and the E-stop devices are used to de-energize it.
Steve

The sad fact is that we deal with a number of OEMs who still use this exact method on new equipment. The "master control relay" is typically a P&B or similar ice cube DPDT, you've seen the setup before I'm sure. Change is very slow for some.