Centroid Community CNC Support Forum

In the Acorn setup Wizard, when selecting inputs, you are given the option of specifying whether the device you are using for the input is "NC" (green dot) or "NO" (red dot).

Unfortunately, the contact type, normally-open vs. normally-closed, is not what you are actually selecting.

Take, for example, CycleStart2 or FeedHold2. Standard industrial practice is to use normally-open pushbuttons for "go" functions such as Cycle Start or jogging; and to use normally-closed pushbuttons for "stop" functions such as Feed Hold, Cycle Cancel, and Emergency Stop.

If I have a normally-open button I want to use as CycleStart2, and a normally-closed button I want to use as FeedHold2, I might reasonably (but naively) select "NO" (red) for my CycleStart2 input, and "NC" (green) for my FeedHold2 input.

Neither one will work properly. The Wizard will set input inversion for the Start button, and not for the Feed Hold button. In fact, the standard Acorn PLC logic expects both CycleStart2 and FeedHold2 to be normally-open pushbuttons, which close when activated. Therefore only my normally-closed Feed Hold button, and not my normally-open Start button, require inversion.

In reality, it seems that what the Wizard means by "NC" is "does not need inversion to work with the standard PLC logic"; and what the Wizard means by "NO" is "needs inversion to work with the standard PLC logic". Hence the incorrect inversion settings in my Cycle Start / Feed Hold example. Presumably the same error would occur with any input for which the standard PLC logic is written for normally-open switches. That would include almost every "start" or "continue" input.

The Wizard should be made aware of the expected state of each canned input, so that it can set/reset inversion based on whether the user specifies a the non-standard switch contact; rather than always setting inversion when the user specifies normally-open contacts.

Also, the "Acorn CNC12 Acorn Wizard Input and Output “canned” PLC functions and M codes" document should be extended to describe, for each input that can be selected, whether the default expectation is for normally-open contacts or normally-closed contacts. Alternately, users might find it easier to understand description that say what a closed input means, and what an open input means.

For example, the description for "CycleStart2" could say "normally-open pushbutton", or could say "input closed (green) when the button is pressed, and open (red) when the button is not pressed".

thanks for the feedback

-I will improve the Wizard input and output descriptions in the documentation to include your suggestions and beef up what we think NC and NO is and means.

in the Acorn world everyone seems to have their own definition of NC and NO.

"Alternately, users might find it easier to understand description that say what a closed input means, and what an open input means."

im sure it can be improved, page 7 covers VLED's NC/NO
https://www.centroidcnc.com/centroid_di ... screen.pdf

and i go over it Ad nauseam in the probe setup guide.
https://www.centroidcnc.com/centroid_di ... _setup.pdf

marty made video a long time ago as well.


- I want to clarify..... to the casual reader of the post the implication is that cyclestart2 and feedhold2 do not work. that is not true, they work just fine and have been for years, unless something has changed (what version are you working with?), maybe they do not work the way you expect? I'm always up for suggestions on how to make things better. so lets review.



fyi..related and in general the intention was that Wizard input names with the letters "Ok" in them are expecting a typical a NC type input. meaning:

NC = input closed = Green input LED = everything is OK

but, you can use these inputs definitions with a NO (switch or sensor) by indicating as such on the Wizard input screen which "inverts" that input.
Virtual input LED is still Green an indication everything is OK, just with line above it as a indication that input is inverted.

is there a better way?

to the casual reader of the post the implication is that cyclestart2 and feedhold2 do not work

They do work just fine, as long as the user installs normally-open pushbuttons and does not overthink it.

If the user tries too hard (as some on this forum demonstrably do), either by using a normally-closed button for feed hold, or by dutifully selecting "NO" in the wizard for their normally-open button contacts, then it won't work.

The wizard should choose the initial default (non-inverted) state based on given data about each input:
e.g. EStopOk = NC, HomeAll = NC, Axis_LimitOk = NC
and CycleStart2 = NO, FeedHold2 = NO, CycleCancel2 = NO

It probably makes as much sense as any to use green for NC and red for NO, indicating the color of the dot on the Alt-i screen when the input is idle (not pressed/tripped/activated). Some may be confused by this being opposite the color convention for pushbutton contact blocks, but so be it.

It would be helpful if the documentation can highlight those cases where the wizard's definition of "normal" is different from the device manufacturer's definition.

Fundamentally, "normal" is what you would measure if you took a new switch out of its box, set it on your desk, and checked continuity: normally-open contacts would be open, and normally-closed contacts would be closed.

For the Wizard's purposes, though, "normal" is as the device is installed on the machine and the machine is ready to run. So, for example, a switch wired in as ATC_AirPressureOk is wired using normally-open contacts; but would be described as normally-closed in the Wizard.