question re. estop logic - (pncconf output)

1:1
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01 Aug 2011 04:57 #12072 by 1:1

Replied by 1:1 on topic Re:question re. estop logic - (pncconf output)

PCW wrote:

And always use active low outputs, so that the built in watchdog can work and the power up state is correct...

I'm eager to learn about this, but at the moment this seems contradictory to what I've said - so I'm wondering why the sentence starts with 'and' instead of 'but' :dry:

I would have thought having a high loop would have been better as if it got damaged the input side would likely earth and go into estop - but if it were low then if it were damaged it could easily connect to gnd and appear to working (i.e. low) no matter what button you pressed to open the circuit ...

How to pull-up and/or pull down resistors fit in here (if at all) ?

I need to read up on watchdog and so on - and also figure out if just starting up the control side of the system before the power side would solve the power up state issue (that combined with chargepump controlled enablers outside of the control).

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andypugh
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01 Aug 2011 12:37 #12082 by andypugh

Replied by andypugh on topic Re:question re. estop logic - (pncconf output)

1:1 wrote:

So, the plan was just to have a little loop coming out of the Mesa card then straight back in with a NC switch in the middle

I suspect that won't work, for reasons that I am fuzzy on related to open-drain pins and suchlike. Also, I don't think it would do what you want if it did work.
You want EMC2 to be aware that E-stop has been triggered, and you want EMC2 to be able to trigger an E-stop. These are two distinct functions.

If you connect your external e-stop switch between the input pin and the adjacent earth, then you should see the state toggle in Halmeter as you operate the switch. This is because input pins, if I remember correctly, have a weak internal pull-up.
This would only be useful for software-only e-stop, as a way to signal to EMC2 that the machine has stopped. You would probably link that to a NO relay linked to the rest of the e-stop chain, not directly to the chain. (After all, informing EMC2 of the hardware E-stop status is of secondary importance). An auxiliary contact on the main power breaker might be suitable.

Allowing EMC2 to activate the hardware e-stop is possibly more difficult if you want to latch the hardware state. I think that might require a purpose-made e-stop relay, and those are very expensive:
uk.rs-online.com/web/p/safety-monitoring-device/6988704/
To be honest, I have no idea what those do, largely due to a lack of interest related to the price.

If it is sufficient for EMC2 to be able to drop out the main contactor, then a simple NC relay in the contactor energisation circuit operated by an EMC2 output would work (you would probably need to buffer this to drive it from a mesa card output)

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btvpimill
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01 Aug 2011 14:26 - 01 Aug 2011 14:53 #12087 by btvpimill

Replied by btvpimill on topic Re:question re. estop logic - (pncconf output)

They are certainly proud of that thing-a-ma-jigy. Having said that, its not to hard to wire your own using 1 output and 1 input.

the output goes like this:

out

o-/-o

any number of switches

coil

gnd (or pwr depending on what an output is)

that will allow emc or a hardware switch to drop the relay

The relay needs to have 2 sets of contacts:

1 set to switch power to the drives
1 set to be the input to the card input.

Then if the machine or the user hits the estop, the relay drops out (as shown above) which in turns drops the signal to the input.. EMC will see that and know there is an estop condition
******************************************************WARNING***********************************************************************
THIS TAKES NO CONSIDERATION OF THE NEEDS OF THE HARDWARE. GREAT CARE MUST BE TAKEN TO ENSURE THE CARD I/O ARE NOT CONNECTED IN A FASION NOT INTENDED BY THE MANUFACTURE.

THIS IS TO ILLISTRATE THE LOGIC ONLY!!!!!!!!!!!!!!!!!

Last edit: 01 Aug 2011 14:53 by btvpimill. Reason: added caution

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PCW
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01 Aug 2011 14:32 - 01 Aug 2011 15:14 #12088 by PCW

Replied by PCW on topic Re:question re. estop logic - (pncconf output)

The FPGA card bare outputs are designed for an active low environment, if you arbitrarily change this because you do not know the implications you will cause lots of problems and will defeat the built in safe guards in the card and firmware.

If you want active high (low = estop) externally sure, but that is what input isolators are for, field wiring a machine of any size should not be done with the bare FPGA pins...

Last edit: 01 Aug 2011 15:14 by PCW. Reason: sp

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btvpimill
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01 Aug 2011 14:50 #12090 by btvpimill

Replied by btvpimill on topic Re:question re. estop logic - (pncconf output)

I should have noted, my above wiring completly disregards the needs of the actual hardware it is being connected to. It is intended to illistrate the logic.

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1:1
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01 Aug 2011 20:08 #12101 by 1:1

Replied by 1:1 on topic Re:question re. estop logic - (pncconf output)

PCW wrote:

The FPGA card bare outputs are designed for an active low environment, if you arbitrarily change this because you do not know the implications you will cause lots of problems and will defeat the built in safe guards in the card and firmware.

If you want active high (low = estop) externally sure, but that is what input isolators are for, field wiring a machine of any size should not be done with the bare FPGA pins...

ok, makes sense - I was getting carried away with my little tester circuit here and not listening/thinking - in reality I'd have the loop at 12v which is what was used in the estop chain of the automation systems I ran backstage (head crushing hydraulics around people). The FPGA would drive that, but in an isolated sense which with small fiddle could be active low.

I still need to read up and ponder on everyones input, then draw from my own sense what I'll do - at least try to think of every failure state then test it rigorously...

I'm back at university now for two weeks and its draining my funds like nothing else - ha ha, do you do student discounts on the I think it was the 7i37 ? :blush:

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doug6949
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01 Aug 2011 21:15 #12103 by doug6949

Replied by doug6949 on topic Re:question re. estop logic - (pncconf output)

andypugh wrote:

I think that might require a purpose-made e-stop relay, and those are very expensive:
uk.rs-online.com/web/p/safety-monitoring-device/6988704/
To be honest, I have no idea what those do, largely due to a lack of interest related to the price.

Banner sells a version of this device in the states for about $175. Automation Direct now carries one for $90.

It's a good investment if you plan on building a machine that will be used by employees. I use them in most machines I build, in part because of legal requirements.

The purpose the separate estop monitor is to have a dedicated device that removes power from the contactors and some PLC outputs during an estop event. One output notifies the PLC/CNC and the other goes to a dedicated safety contactor (another $48).

The monitor has three inputs, one from the PLC/CNC and two for dual loop estop switches.

Doug

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1:1
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01 Aug 2011 21:22 #12104 by 1:1

Replied by 1:1 on topic Re:question re. estop logic - (pncconf output)

got the links to those Banner and Auto direct versions ?

If they have the same rating or whatever makes them legally defined as appropriate (as in required to be signed off by some engineering type) then I'd like to read up on them

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doug6949
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01 Aug 2011 23:31 #12108 by doug6949

Replied by doug6949 on topic Re:question re. estop logic - (pncconf output)

The Banner part number is ES-FA-9AA. The Banner site, like their catalog, is difficult to use. Look for the PDF on this model as it is informative.

For Automation Direct, the best thing is to type "safety monitor" in the search box. It will bring up all models from basic to absurd.

The safety relay is McMaster Carr part # 7230K881. Or you can search safety relays and it will bring up the catalog page. They are called "DIN-rail mount screw terminal relays", near the bottom of page 894.

I have several PDF's that discuss EN/IEC estop categories. Let me know if you need anything and I can email them from the office tomorrow.

I also have a wiring diagram of the estop circuit for a machine we recently built - can send a DXF if you need a place to start.

We build controls for 110 ton textile presses. I spent over a year learning the rules for safety circuits. Glad to help if I can. Then I won't feel guilty about all the questions I'll soon be asking about EMC.

Doug

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1:1
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01 Aug 2011 23:47 #12109 by 1:1

Replied by 1:1 on topic Re:question re. estop logic - (pncconf output)

That'd sure be interesting - will PM you my email !

Cheers,
Nick

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