Prox Switch Help [Resolved]

[Gary Campbell]

I'm right with muzzer on this one. And .... after some bench testing with some good AND some cheap prox sensors, if using more than two, I would much rather connect 3 NO sensors in parallel than 3 NC in series.

As for the NO vs. NC debate, there is no doubt of the self audit benefits of the NC versions, but for most DIY routers, which don't have the power to destroy themselves, I don't see what the big deal is. IMO, I would rather use cheapo Chinese NO sensors individually wired than 3 expensive sensors series wired as HomeAll, which is a kludge at it's very best

[cncbuiltbyme]

Thanks Gary, ShawnM and Muzzer... now looking into and testing NO in parallel and three separate inputs, really appreciate the feedback.

[Gary Campbell]

Thanks Gary, ShawnM and Muzzer... now looking into and testing NO in parallel and three separate inputs, really appreciate the feedback.

That is far and away the best way to both understand the process and get your machine working the way you desire. Test a couple different ways with a couple different products to see what works best for you. As you can see, based on our experiences, guys like Shawn and I are often on opposite sides of an issue, both have working results, neither is right or wrong, just different. Test to see what works best for you.

[CNCisRobot]

Hi All,

This is how I solved the prox sensor issue. I designed a small board that you wire 3 sensors in and then 0V. 12V power and a switched relay output switching ground. With the relay energised the NO contact on the relay is closed, this then meets the acorn ideal requirement of an active normal good position. Then if a sensor breaks or wire cut or unplugged or sensor senses the stop the relay is switched off and the acorn then sees the sensor trigger. Because it is an active switched relay output it also means you can connect the board to another board for 6 prox sensors or more as many as you need.

I am new to this CNC and I have so far built the control box got my spindle and 4 servo motors just not got a machine to control yet. I have designed a machine but need to build it!

[ShawnM]

Now you are adding in another variable with multiple failure points for something that should be so simple.

There are many videos from professional companies on wiring in series and even Omron has documentation, diagrams and formulas for calculating minimum voltage when wiring in series. They even mention erroneous pulses of about 1ms when one is powered up while in series. Test the circuit BEFORE you install it on the machine. Here's a link to Omron's website with some useful formulas when wiring in series.

https://www.omron-ap.com/service_suppor ... /index.asp

As Gary mentioned, there will always be a difference of options on how to wire home/limit switches and what type to use and why. Neither are right or wrong. Find what works best for your machine. There's best practice and then best practical. The best part is you get to choose.

[CNCisRobot]

I think the Omron parallel would work, but it does not have all the advantages of the way I am implementing it. Mine is very expandable have as many sensors as you like just use more boards and connect them in series because of the NO active relay output. Plus it will show sensor disconnect or wire broken and is active contact which is what Acorn likes. I am using 2 boards 1 is for home with 3 sensors and 1 is for limit with 3 sensors, I think this works fine for me. I am new to all this and thought I would just share for others to see if they find this useful.

[BrixhamEngineer]

Thanks ever so much for the wiring diagram. I couldn't get it to work originally as for some reason, I thought the input line (black) was the only one to put in series. Because of the amount of time trying to sort it I decided to give up and use up more of the inputs, so each proximity switch was wired separately.

However, since I'm still in the bench testing stage, I thought it worth trying to wire as per diagram. Pleased to say it worked first time, so many thanks. Another box ticked on the way to finishing the conversion from MASSO (on the Sherline Mill and Lathe) to Acorn.

Many thanks,

Mike

[ShawnM]

Here's my Acorn diagram for wiring 3 prox sensors in series to Input 1 set as "HomeAll". Please use 24 volts for your power. See the notes at the top of the page in red. I have wired Omron to cheap Chinese Roko sensors found on Amazon this way with zero issues. This may or may not work for all NPN switches on the market but I have not found one that didn't as of yet.

[Spartan117]

You could also trigger an extra little relay with every prox sensor and wire the relays in series (NC-contacts used).
So you 'd get a NC-circuit for your acorn and cables and still be able to use every prox sensor you want to, even mixed.
The small relays are very fast, too, about 8-10ms, and as the delay is always the same, there is no precision loss at all.

Like this you also could wire much more sensors in series without problems.
Many older machine controls worked that way, too. I even use that on my router for many years now, without any problems.
And the Emcoturn is using NPN NO sensors, so I did that there, too.

[ShawnM]

Sure, you could also wire in relays but now you are adding in another mechanical failure point and a source for electrical noise if a diode or snubber is not used. Why? You only need one switch per axis, that's 3, (of course this will start yet another debate ) how many more do you want to add in? I don't feel the need to over complicate something that is very simple and easy to do. Three NC prox sensors either wired to individual inputs (the preferred way) or series three together to one input and you're done. On to the next step.