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SOLVED - Answer at bottom

Hello All -

I am trying to wire up a homing switch using a NPN NO Proximity sensor on my mill.

One of the switches I am using / testing is: https://www.ebay.com/itm/141835552905 I have searched a good bit and reviewed schematic#: S14955 (https://www.centroidcnc.com/dealersuppo ... 955.r5.pdf) but I still have some questions.

My question / concern is: can the acorn input ports take a positive non COM voltage?

As seen in schematic S14955 - the black output wire from the switch goes straight into the acorn input. I am assuming that that black wire will be either high/low (NO / NC) with whatever voltage is required to run the switch. When I wire up my switches for testing using a 24v power supply I get 24v at the black output wire, which would be wired directly into one of the inputs available on my acorn.

The reason for my question / concern is that in every other input wiring situation, the input is receiving a ground / COM signal (Example: https://www.centroidcnc.com/dealersuppo ... 954.r5.pdf).

I just want to double double check before I fry something on my board.

Sorry if this is really obvious or has been answered somewhere else ....


Answer

High level - there is 24V at the input terminal and it reads when ground (or lower voltage is found). So if you send 24v or the same voltage into the input pin nothing will happen since that voltage is already there.

Go with S14955, it works

Uwe

I've used those Omron knock-off sensors. They are open collector normally open (although they are also available as normally closed). The 24V you are measuring is due to the pullup resistor within the Acorn. This pulls the input up to 24V when there is no path to ground via the switch. As the 24V is supplied by the Acorn itself, it's not going to be a problem.

These sensors detect eddy current losses in the metallic target, so in fact the detection (trigger) distance is shorter if you use a higher conductivity target such as aluminium or copper rather than iron or steel. Arguably, that might improve the repeatability slightly.

For future reference normally closed switches are preferred but these will work.

And as pointed out by Muzzer, those are NOT Omron switches. They might be Omran but certainly not Omron.

Thanks all for the replies -

Muzzer wrote: ↑Thu Dec 28, 2023 1:01 pm I've used those Omron knock-off sensors. They are open collector normally open (although they are also available as normally closed). The 24V you are measuring is due to the pullup resistor within the Acorn. This pulls the input up to 24V when there is no path to ground via the switch. As the 24V is supplied by the Acorn itself, it's not going to be a problem.

These sensors detect eddy current losses in the metallic target, so in fact the detection (trigger) distance is shorter if you use a higher conductivity target such as aluminium or copper rather than iron or steel. Arguably, that might improve the repeatability slightly.

The testing I conducted is without the acorn just switch and power supply and triggering object - but I think I understand.... the high level is that it doesn't matter because there is 24V at the input terminal so long as you are using the same power supply (or voltage) as the 24V in pin youre good. I also ran out to test the board and there is 24v at the input pins - so thanks for helping me!!!

ShawnM wrote: ↑Thu Dec 28, 2023 1:36 pm For future reference normally closed switches are preferred but these will work.

And as pointed out by Muzzer, those are NOT Omron switches. They might be Omran but certainly not Omron.

.... F-Omron ... Fake Omrons.. yeah these are totally knock offs but I bought them to test.. I also got some nicer Baumer sensors to see if there is a difference in accuracy.

I do regret not paying more attention to the add and buying normally open.... but what can you do

killacam wrote: ↑Thu Dec 28, 2023 2:04 pm The testing I conducted is without the acorn just switch and power supply and triggering object - but I think I understand.... the high level is that it doesn't matter because there is 24V at the input terminal so long as you are using the same power supply (or voltage) as the 24V in pin youre good. I also ran out to test the board and there is 24v at the input pins - so thanks for helping me!!!

Interesting - these are supposed to be open collector, so the output should require a resistor to pull the output up to the supply voltage when no target is detected. The various "Omwrong" sensors I got behaved correctly and work fine but perhaps they come from a different copy shop. No matter - if they work, use them.

As for using normally open, you can parallel several up onto one input (eg set it up as "HomeAll") - that way you save multiple inputs. It's true that it is considered better practice to go for normally closed (to protect against broken wires etc), although there is no "approved" method of connecting 3-wire NC sensors in series if you want to common them up. Some people do this and it seems to work but when you consider how these things function internally, it's not possible to define exactly how they will behave.

Muzzer wrote: ↑Fri Dec 29, 2023 10:34 am .....although there is no "approved" method of connecting 3-wire NC sensors in series if you want to common them up. Some people do this and it seems to work but when you consider how these things function internally, it's not possible to define exactly how they will behave.

What you say is true Muzzer, there is no approved way to do this. I'm happy to report I've been wiring my systems this way for the past four years now to save inputs and have not had any issues to date. Always using various NPN NC proximity sensors wired in series to a single input set to "HomeAll". I only wire them using 24 volts, nothing less. Others may see different results.