Hello Guest it is January 18, 2020, 05:30:31 PM

Author Topic: Normally Open VS Normally Closed  (Read 11120 times)

0 Members and 1 Guest are viewing this topic.

Re: Normally Open VS Normally Closed
« Reply #30 on: August 13, 2016, 05:44:58 PM »
You are dead on.  M8 just don't go no matter what.  Steve Jobs would roll in the grave.  Not that I am an Apple fan, but the man understood and defined out of box experience.

Re: Normally Open VS Normally Closed
« Reply #31 on: August 13, 2016, 06:17:26 PM »
So basically, as often happens, my last 4 or 5 post are crap.  I was testing the M8 function and jumped to a bunch of conclusions.  Thought I would roll on and outsmart the creators.  But turns out if you want M7,8, and 9, you will configure them in Mach Ports and Pins and live with their functionality.  If And But Else, you will write your gcode to use a custom M??? command that's not standard if you don't like it.
Tis What Tis

Offline Hood

*
  •  25,856 25,856
  • Carnoustie, Scotland
    • View Profile
Re: Normally Open VS Normally Closed
« Reply #32 on: August 13, 2016, 06:37:15 PM »
There are often other ways to do things, such as, as you say, custom macros for coolant etc.
 For example if you really wanted to have the message in the ticker when coolant was switched on/off then that could still be accomplished. Have the macropump watch the state of the Flood LED and send the appropriate message. The only thing is it would constantly be there unless you could code in such a way that it was just a one shot. I am crap at VB but I am sure others could manage.

Hood
« Last Edit: August 13, 2016, 06:40:12 PM by Hood »
Re: Normally Open VS Normally Closed
« Reply #33 on: August 13, 2016, 06:48:03 PM »
I get that.  My Message "Coolant works"  was just a quick troubleshooting "catch".  It worked.  I caught a weird Mach situation, posted to forum, got a response about M7,8 and 9 being "real odd ball".  Worked perfectly.

Theres almost always a work around.  I get that.  One brand has this interface.  Try it.  If what you are trying to do doesn't work, just try it another way.  Every major league brand out there has their issues.  Everyone one of them.

Thats the way it works in any multivendor system.  Documentation is what sets them apart.  And I hate documentation.  Most undervalued "cost of doing business" in my world.  It takes forever and is never done.

Offline Hood

*
  •  25,856 25,856
  • Carnoustie, Scotland
    • View Profile
Re: Normally Open VS Normally Closed
« Reply #34 on: August 13, 2016, 07:40:15 PM »
Agree there for sure regarding documentation. It is one of the best things but also one of the hardest things to do right.
Mach changed that fast it was impossible to keep up and documentation writing is an art in any case.
It has to be complex enough to cover everything but also has to be written in a way that is understandable to everyone (within reason). It also needs to be possible to quickly find the section that contains the info you need without having to trawl through hundreds of topics which only partially relate to what you want.
So in essence it is a thankless task and often an impossible task.

I have just been wading through the documentation for the DL06 PLC, it is excellent in many respects but finding what I wanted was hard, especially when I didn't really know what I was looking for :D

Hood
Re: Normally Open VS Normally Closed
« Reply #35 on: August 13, 2016, 07:55:40 PM »
Agreed,
I used an Automation Direct drive on this conversion (can't beat the price).  Their documentation on Sinking and Sourcing outputs is dead wrong.  And they only did the one I didn't want to use (sinking output).


Off topic,  Never use sourcing inputs on a drive.  Meaning you connect their drive input signal to ground to make it go.  If a wire gets shorted to ground, off goes that drive.  Maybe that is right back on original topic.

Offline Hood

*
  •  25,856 25,856
  • Carnoustie, Scotland
    • View Profile
Re: Normally Open VS Normally Closed
« Reply #36 on: August 13, 2016, 08:12:28 PM »
If my memory serves me right the DL06 can be set either way (in banks of 4) . For me I like Sourcing outs and Sinking Ins, just seems natural that way :D

Seems to be a lot of the Asian servo drives like to have sourcing Inputs, why I have no idea but it is often a PITA and as you say can be dangerous.

Hood
Re: Normally Open VS Normally Closed
« Reply #37 on: August 13, 2016, 08:45:59 PM »
The asians got this one wrong.  As I stated earlier in this post, safety requires forward thinking.  If a wire gets cut- we should predict the state.  No sane person won't understand that a wire that got cut will very likely go to ground or be cut clean......  It could short to another hot wire but the odds are stacked way against that.

So, when the asian drive folks opt for grounding the input to make it run, they clearly haven't progressed through the lawsuits.

Most PLC's can do the bank of X number of inputs or outputs.  For example, Inputs 0-3 may share the same "common" (not to be confused with DC Com).  If you connect the DC Common to this terminal, this provides a path to ground or specifically DC Common.  So if 24 VDC shows up on any one of 0-3, it will allow current to flow to the "common" terminal because you connected DC Common or ground to that terminal. Howerver, if you hook up 24vdc to the common terminal.  In that case, when you apply 24 vdc to one of those inputs (0-3), no current will flow because 24vdc is on both sides of the circuit.  The Input will not be activated.  In the same setup (24 on the common),  If you ground or connect dcComm to one of the inputs, current will flow "backwards" (thats highly debatable) and the input will register.

It is very useful to have banks of inputs that are selectable for sinking or sourcing.  Case in point is the Automation direct drive I have.  It will only provide a sinking output (meaning it provides a DC Common when ON).  The only way to use this directly is connect 24vdc to my "common" for some output and let the drive provide a ground or DC Common.  This will activate the input.  This is why CSLabs has all those dedicated connections for each input.  If, Like PLC manufactures generally do, they banked 4 at a time, I would waste 4 inputs if only one of my inputs required a sourcing input (meaning current needs to flow out of the input- to the drive------highly debatable again).


Re: Normally Open VS Normally Closed
« Reply #38 on: August 13, 2016, 09:11:12 PM »
To simplify the safety issue.

Imagine standing in front of your machine.  Floor is wet, you happen to be barefooted today with bud lite in your left hand.  You reach out and turn a simple switch to make something go.

Switch is an old/current barrel type swicth that is really a fwd/rev switch that is wired 3 phase 480 volt.  Your spilled bud lite has grounded your bare feet.  That high voltage is 1 inch behind the aluminum face plate you made.  But, your spilled beer has bonded you (like it or not) and there is actually a clean path from the barrell switch contacts to ground through you fingers and bare feet.  NOT GOOD.

So, many years ago, it was figured out that it is much safer to remove high potential voltages from operators.  Two things happened and two thought paths occurred.

Lets only have the neutral or ground (most neutrals are grounded) on the switch panels.  Sounds great.  If you are standing in water and touch a switch that can only provide ground, no current can flow.  Perfect.
Except that, now when wires get damaged, the likely hood is they go to ground and activate the signal. Not so perfect.

The other thought (And I agree with this one) is to minimize the voltage potential at the operator switch.  At first, 120VAC was good enough.  Now we want lower voltages and DC would be good.  So, 24vdc is the standard.  It is really hard to die (or even notice) while touching a switch that is powered by 24vdc with an appropriate circuit breaker (don't forget that one).
Re: Normally Open VS Normally Closed
« Reply #39 on: August 13, 2016, 09:19:54 PM »
Wow..l Sound like an old dude.  Kinda sux.