Inductive Limit Switch problem

I've just upgraded from using microswitches as limit/homing switches to LJ12A3-4-Z/BX type inductive proximity sensors. I'm getting some spurious trips from the Z-axis sensor due to interference from the spindle, a Huan Yang 2.2kW water cooled unit fed from a VFD. The spindle and sensor wiring go through the same drag chain for part of the run and I'd like to avoid having to separate them if possible.

One of the symptoms is that the red LEDs on the relevant sensors glow visibly, but very dimly, when the spindle is running. A ferrite ring on the sensor cable makes no difference, neither does a 1uF capacitor between ground and either the +V supply or sensor output.

Has anyone else seen this faint glow before and, if so, how did you fix it?

All help gratefully received.

Kit

Are the wires from the VFD output to the motor shielded in any way?

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Originally Posted by Kitwn

Has anyone else seen this faint glow before and, if so, how did you fix it?

All help gratefully received.

Kit

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I've seen this before when the voltage is close to the minimum 6v. I've also seen it when wired wrong but can't imagine you've done that. Another thing that often happens is the switch can be marked up wrong ie: NPN when should be PNP or NC when NO.

What voltage and breakout board are you using.?

Are you using the cable attached to the sensors? When I was wiring up my machine I noticed that the cable wasn't errrm exactly up to the standards Auntie Beeb would have liked, so extended with screened twisted pair: not had any problems at all, even running the spindle up to 900Hz (12.5KHz carrier)

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Originally Posted by JAZZCNC

I've seen this before when the voltage is close to the minimum 6v. I've also seen it when wired wrong but can't imagine you've done that. Another thing that often happens is the switch can be marked up wrong ie: NPN when should be PNP or NC when NO.

What voltage and breakout board are you using.?

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The VFD cable is screened, earthed at the VFD and connected to the spindle body. Just writing that makes me wonder if there's an earth-loop because of that. Must try removing the spindle from it's bracket.

It all worked fine before I started the spindle! I'm using a basic cheapo Chinese parallel BO with diodes to isolate the 5V on it's inputs from the higher sensor voltages. I originally installed the sensors with 12V and have tried 24V but still get the same slight glow on the LEDs.

I have known issues with the BO inputs not being pulled down far enough by the sensors. I can fix that, it's the slight glow and my inability to fix it with filtering that worries me most at the moment. I was wondering if it was a known issue. If somebody is getting the same symptoms but still has the sensors working reliably I'll be happy.

Quote:

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Originally Posted by Kitwn

The VFD cable is screened, earthed at the VFD and connected to the spindle body. Just writing that makes me wonder if there's an earth-loop because of that. Must try removing the spindle from it's bracket.

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That would be my first move. It's a much debated thing but I never ground both ends and I never have issues with these cheap sensors. Thou like voice coil mentions I cut the shitty cable off close to the sensor and use screened back to the board and ground it.

I had very similar problems until I did this.

https://www.youtube.com/watch?v=DJfiOqaeFDg

Simon

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Originally Posted by Kitwn

It all worked fine before I started the spindle! I'm using a basic cheapo Chinese parallel BO with diodes to isolate the 5V on it's inputs from the higher sensor voltages. I originally installed the sensors with 12V and have tried 24V but still get the same slight glow on the LEDs.

.

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Mmmm, just had a thought..... any chance you could post a little pic of the exact arrangement please? The way I'm reading the above, you're using only the bottom 5V of the voltage swing, and hence will only get the noise immunity of a 5V system - having a series resistor or resistive divider would be better. However I may be reading it wrongly!

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Originally Posted by JAZZCNC

That would be my first move. It's a much debated thing but I never ground both ends and I never have issues with these cheap sensors. Thou like voice coil mentions I cut the shitty cable off close to the sensor and use screened back to the board and ground it.

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That will be test one. How many layers of cling-wrap do you think I'd need round the spindle to insulate it from it's bracket if that works?

Interestingly I get the same amount of glow from two sensors. The Y one which goes to a junction box and onto screened cable before joining the VFD cable in the drag chain, and the Z which has the original cable running in a common length of drag chain before being connected into the same (8way) screened cable as the Y.

Voicecoil,
I do take the point about cutting off the original cable short and going screened, I shall probably do that anyway. Possibly with some balanced audio cable if I have enough, it's thinner than the other stuff I have in stock and Auntie would surely approve.

Simon,
I'll have a look at the full video tomorrow, but I've tried winding a few tuns of the cable onto a ferrite ring at the sensor end and adding capacitors as described earlier at the joint into the multicore. Much to my disappointment it made no difference. Next will be to hook up my oscilloscope and look at the noise level with different solutions.

I'm between 12 hour shifts tonight (and very glad to be still working) so it will be Wednesday before much more gets done on this. Thanks for all the input everyone.

PS I have this cunning design for a low cost DIY optical fibre interface that would solve all these problems but I really would like to get the machine upgrades finished right now and actually make something with it!!!

Funny how the brain works. There I was, lying in bed reading a book when I suddenly realised what an idiot I was for suggesting screened audio cable for this application. Not enough wires!

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Originally Posted by Kitwn

That will be test one. How many layers of cling-wrap do you think I'd need round the spindle to insulate it from it's bracket if that works

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2 wraps should do it, don't want to waste it you'll need it for when the Loo roll runs out.!

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Originally Posted by Kitwn

Funny how the brain works. There I was, lying in bed reading a book when I suddenly realised what an idiot I was for suggesting screened audio cable for this application. Not enough wires!

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It depends on the polarity of your switches and how you're wiring them. NPN NO in parallel (possibly not the optimum choice) could work fine with twin screened, likewise PNP NC in series could work, as both have a commoned 0V - assuming your 24V ground is connected to chassis somewhere of course. Otherwise there's plenty of smallish 3 & 4 core screened cables available, I've a few bits of Mogami 2790 which have come in useful.

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Originally Posted by JAZZCNC

2 wraps should do it, don't want to waste it you'll need it for when the Loo roll runs out.!

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I'm really not letting my imagination go there! A DIY bidet is more likely.

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Originally Posted by Voicecoil

It depends on the polarity of your switches and how you're wiring them. NPN NO in parallel (possibly not the optimum choice) could work fine with twin screened, likewise PNP NC in series could work, as both have a commoned 0V - assuming your 24V ground is connected to chassis somewhere of course. Otherwise there's plenty of smallish 3 & 4 core screened cables available, I've a few bits of Mogami 2790 which have come in useful.

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I'm really not happy with the idea of powering up electronic devices on the 'just in time' principle that series connection of these sensors involves. In practice the four I have are all independent anyway, X1, X2 , Y, Z.
The ones I have are NPN NO which seem to be the most common on eBay. I'm not sure if I have much 4-core screened left but have plenty of 8-core. At present I'm running the supplied 3-core cables to a junction box on the back of the Z axis where the Y & Z cables connect into an 8-core screened cable back the the controller.

When I come to do mine in the future I'll wire them in series for each axis and use solid core CAT7 cable.
Where I have to split it down from 8 wires into pairs as I get closer to the machine I'll heatshrink them.
CAT7 has each pair shielded already. It's just a case of carefully getting the outer sheath off without damaging the foil on each pair.

Atm I'm just using the soft limits.

Quote:

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Originally Posted by Kitwn

I'm really not happy with the idea of powering up electronic devices on the 'just in time' principle that series connection of these sensors involves. In practice the four I have are all independent anyway, X1, X2 , Y, Z.
The ones I have are NPN NO which seem to be the most common on eBay. I'm not sure if I have much 4-core screened left but have plenty of 8-core. At present I'm running the supplied 3-core cables to a junction box on the back of the Z axis where the Y & Z cables connect into an 8-core screened cable back the the controller.

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As per the previous post, combining these switches in series isn't a probem as you combine the switches at each end of the same axis - don't mix axes. As long as you have each axis (including A and X if it's a dual-axis machine) going to a separate input, that also lets you home more than one axis at a time. You need to do that anyway if you have a dual-axis machine and want proper gantry squaring on homing.

Personally I run spindle, motor, and switch cables all in the same cable chain; they are all CY and I use 24V signalling which helps with noise rejection. Don't have noise problems.I do have a solid earth wire running through each cable chain connecting the two end parts to avoid any need for continuity via the bearings. Haven't noticed the LEDs glowing. I did wonder if you had bad switches; I bought a cheap box of 10 from eBay when I built my machine and one was the wrong type (only had two wires coming out which was a bit of a giveaway), one was bad when I fitted it, and one failed shorty afterwards. Been OK since, though.

If you are looking for 3 core shielded you might find an old USB cable which is shielded (some are, some are not).

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Originally Posted by dazp1976

When I come to do mine in the future I'll wire them in series for each axis and use solid core CAT7 cable.
Where I have to split it down from 8 wires into pairs as I get closer to the machine I'll heatshrink them.
CAT7 has each pair shielded already. It's just a case of carefully getting the outer sheath off without damaging the foil on each pair.

Atm I'm just using the soft limits.

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Nice idea for fixed sensors but I don't think solid core cable will last long in a moving drag chain.

Neale,
X1 and X2 are for squaring the gantry. The only axis with two switches is X2. I've left the old mechanical microswitch at the other end of that one just in case the soft limits fail to stop a crash for some reason. Shouldn't ever be needed in practice.

I used NO switches to make interfacing 12V switches to a 5V BOB simple. Everything worked fine until I started the spindle. My circuit failed to work when I tried using 24V so a more complex interface will be required anyway. NC would have been better for the reason that broken wires show up immediately instead of causing a crash when you try to home the machine, but I'm not buying a new set now. I'm going to get the oscilloscope out and have a look at the noise, then some experiments will be needed to devise a reliable solution. I'll publish details once I have something useful to say. I might even make a video for everyone to watch while in lockdown!

I didn't get time to look at the noise today but did manage to trace the input circuit for the cheap BOB. Picture below.
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The inputs each feed one gate of a 74HC14D hex (that's six in one package) inverting Schmitt trigger. Exactly the technology I would have chosen for such an application myself!
There's a 10K pull-up resistor on the input and a 100pF capacitor to add a (very) little filtering.
Most interestingly, there's also an 1K resistor between the PCB header input and the screw terminals. This means that, when pulled low by an external circuit, using the screw terminals will leave the input to the trigger at about 0.4V higher than using the header connection. Since the low threshold for the trigger can be as low as 0.9V (typical value is around 1.3V with a 5V supply) this makes a big difference to how the circuit will behave, especially if you're not using a mechanical microswitch which provides a solid connection to ground.
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Having just changed from microswitches to proximity switches with an isolating diode as well it's no wonder I'm having problems. The circuit below shows how I have the sensors wired into the BOB using a 1N4148 diode to isolate the 5V input from the 12V or 24V supply to the sensors.
The saturated output voltage of the sensor when triggered is about 0.3V. Add the usual 0.6V we see across a forward biased diode and that leaves 0.9V. BUT the current flow of about 0.4mA from the 5V supply through the 1K resistor lifts the input to the gate to 1.3V. This is right on the edge of the gate's lower threshold. All 4 sensors worked fine with a 12V supply before I fired up the spindle but very little noise is required to trigger a spurious trip. With a 24V supply the saturated output of the sensors rose less than 0.1V but this is enough not to trigger the inputs at all, even with no spindle noise.
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Next move will be to connect the inputs to the PCB headers and see if the extra 0.4V of headroom clears the problem. I don't always get spurious trips so this might be enough.
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I'm going to order a reel of 4-core screened cable from RS anyway, cut the tails off the sensors and wire them back to the connector panel without any other junctions.
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What the diagram does not show is that I have 1uF capacitors across the screw terminal inputs for additional filtering. This was necessary to avoid spurious trips with the microswitches. These will also need to be moved to the PCB headers.
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Attachment 27695

Attachment 27692

Quote:

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Originally Posted by Kitwn

Next move will be to connect the inputs to the PCB headers and see if the extra 0.4V of headroom clears the problem. I don't always get spurious trips so this might be enough.

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Interesting analysis. Re. the PCB headers, the only caution in a high noise environment is the protection of the '14 inputs to >5V spikes. The IC should have clamp diodes that should work to protect but worth bearing in mind.

I have to admit all my cheap boards have had opto isolated inputs which I think can only help for noise immunity for systems like this.

Quote:

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Originally Posted by Kitwn

I didn't get time to look at the noise today but did manage to trace the input circuit for the cheap BOB. Picture below.
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The inputs each feed one gate of a 74HC14D hex (that's six in one package) inverting Schmitt trigger. Exactly the technology I would have chosen for such an application myself!
There's a 10K pull-up resistor on the input and a 100pF capacitor to add a (very) little filtering.
Most interestingly, there's also an 1K resistor between the PCB header input and the screw terminals. This means that, when pulled low by an external circuit, using the screw terminals will leave the input to the trigger at about 0.4V higher than using the header connection. Since the low threshold for the trigger can be as low as 0.9V (typical value is around 1.3V with a 5V supply) this makes a big difference to how the circuit will behave, especially if you're not using a mechanical microswitch which provides a solid connection to ground.
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Having just changed from microswitches to proximity switches with an isolating diode as well it's no wonder I'm having problems. The circuit below shows how I have the sensors wired into the BOB using a 1N4148 diode to isolate the 5V input from the 12V or 24V supply to the sensors.
The saturated output voltage of the sensor when triggered is about 0.3V. Add the usual 0.6V we see across a forward biased diode and that leaves 0.9V. BUT the current flow of about 0.4mA from the 5V supply through the 1K resistor lifts the input to the gate to 1.3V. This is right on the edge of the gate's lower threshold. All 4 sensors worked fine with a 12V supply before I fired up the spindle but very little noise is required to trigger a spurious trip. With a 24V supply the saturated output of the sensors rose less than 0.1V but this is enough not to trigger the inputs at all, even with no spindle noise.
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Next move will be to connect the inputs to the PCB headers and see if the extra 0.4V of headroom clears the problem. I don't always get spurious trips so this might be enough.
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I'm going to order a reel of 4-core screened cable from RS anyway, cut the tails off the sensors and wire them back to the connector panel without any other junctions.
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What the diagram does not show is that I have 1uF capacitors across the screw terminal inputs for additional filtering. This was necessary to avoid spurious trips with the microswitches. These will also need to be moved to the PCB headers.
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Attachment 27695

Attachment 27692

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If it were me I'd be doing the following:

1) Add a decently low (<= 2K2) pullup on the output of the switch to 24V
2) remove the diode
3) Increase R2 to 10K
4) add a 2K7 resistor across the PCB header pins
5) up C1 to at least 10nF
6) remove R3

This should give a decent voltage swing on the switch output and a 0.1....+4.5v ish swing on the input to the 'HC14 with a bit of filtering and a 12dB attenuation of noise on the switch output to boot.

Quote:

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Originally Posted by Kitwn

Nice idea for fixed sensors but I don't think solid core cable will last long in a moving drag chain.

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I won't be going through the drag chain. The switches will be fixed to the machine casting so they won't be moving. The little angle plates they will read off will be axis attached. This way the cable won't need to be that flexible.

Quote:

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Originally Posted by Voicecoil

If it were me I'd be doing the following:

1) Add a decently low (<= 2K2) pullup on the output of the switch to 24V
2) remove the diode
3) Increase R2 to 10K
4) add a 2K7 resistor across the PCB header pins
5) up C1 to at least 10nF
6) remove R3

This should give a decent voltage swing on the switch output and a 0.1....+4.5v ish swing on the input to the 'HC14 with a bit of filtering and a 12dB attenuation of noise on the switch output to boot.

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After I put up the last post I thought for a while and realised that using a diode was the wrong way to do this and that a simple potential divider with the BOB input seeing the open collector of the sensor directly was a far better idea as you suggest. I have a spare sensor and a spare BOB (that's one of the advantages of using a cheapo board instead of a $900 one) so I'll try those component values and check the volts. Thanks for working out the values.

It's tempting to try replacing the surface mount components on the BOB but I think an external bit of Veroboard with all the new bits soldered on will be the best option.

Doddy,
Come to think of it, I've probably got a quad opto-coupler or two in stock though I'll need to print up a surface mount PCB to use one of those. I feel a rummage through my drawers coming on!

Does Mach3 disable limits when homing, or is this an option?

I am not able to look at my machine as it is currently on the floor in my office, which I am refurbing.
Attachment 27706

Looking back through threads (to 2016), I sort-of answered this question, but left doubt. I use a NO inductive switch for homing, but a NC microswitch for limits and I just thought that a break in the homing circuit could cause a crash if the limit is deactivated.

Quote:

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Originally Posted by cropwell

Does Mach3 disable limits when homing, or is this an option?

I am not able to look at my machine as it is currently on the floor in my office, which I am refurbing.
Attachment 27706

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Wow, using CAD to plan your workshop refurb!

OK, after serious consideration my priority has to be getting the #$%^*&^%$#@ing machine actually working so I can make some stuff with it. Playing about with circuit ideas is fine, but...

I'm not wasting a long weekend off work waiting for RS to send me some new cable and other components including 2mm pitch plugs for the PCB headers, so I've made a circuit board which connects into the existing screw terminals without the need to remove/replace surface mount components on the BOB itself. I expect it's going to work. If so, it'll do for now and I'll make a more reliable change to the wiring later. This machine is after all just a toy in my shed rather than the heart of a commercial operation.
Watch this space for details if it works!

Quote:

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Originally Posted by Voicecoil

Wow, using CAD to plan your workshop refurb!

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Notice that Mach3 is already loaded :biggrin:
Attachment 27707

Thankfully, I had all the cabinets and worktop (25mm moisture proof MDF, 800mm deep) delivered before lockdown. All the carcases are built and in position. Next job is the worktops, and they are heavy sheets.

Anyway, My question is about homing and limits and I cannot find any reference to the query in the Mach3 reference manuals.

Quote:

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Originally Posted by cropwell

Anyway, My question is about homing and limits and I cannot find any reference to the query in the Mach3 reference manuals.

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Mach3 certainly disables limits when homing if you use common home and limit switches. Seems likely that it does the same with separate switches - I'm sure I remember reading this in the manual somewhere but that was a long while ago.

Quote:

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Originally Posted by Kitwn

I have a spare sensor and a spare BOB (that's one of the advantages of using a cheapo board instead of a $900 one) so I'll try those component values and check the volts.

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Nope, that's no advantage because if you had a decent board you wouldn't have this problem in first place and this thread wouldn't exist.!! . . . Throw the bag of shite in the Bin and buy a decent board. While you are at it spend a bit more buy one with Ethernet...:joker:

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Originally Posted by JAZZCNC

Nope, that's no advantage because if you had a decent board you wouldn't have this problem in first place and this thread wouldn't exist.!! . . . Throw the bag of shite in the Bin and buy a decent board. While you are at it spend a bit more buy one with Ethernet...:joker:

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I've got a crappy £5 board on my benchtop machine and it works well for me but I only have the estop connected no physical limit switches as yet.
Haven't figured out my spindle wiring either, still doing that manually :smile:
1 question from me is that,. If I have a NO estop I'll need NO limit switches yes? Or does it not matter if estop is NO and limits are NC?

I plan on getting an ess in the future and use one board running axis/spindle and one board running estop/limits.

Quote:

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Originally Posted by dazp1976

I've got a crappy £5 board on my benchtop machine and it works well for me but I only have the estop connected no physical limit switches as yet.
Haven't figured out my spindle wiring either, still doing that manually :smile:
1 question from me is that,. If I have a NO estop I'll need NO limit switches yes? Or does it not matter if estop is NO and limits are NC?

I plan on getting an ess in the future and use one board running axis/spindle and one board running estop/limits.

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You think it works well because you have nothing to compare it against.! When you get the new controller with higher pulse freq etc you'll see the difference.

Regards the N/O question then provided you use separate inputs then you can use different switch types. Obviously if wiring in series and sharing the same input they must all be the same type.

Also if your thinking to buy Warp9 ESS then I'd look at others like UC300 because they are better than ESS and you are not stuck with mach3/4.

Quote:

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Originally Posted by Neale

Mach3 certainly disables limits when homing if you use common home and limit switches. Seems likely that it does the same with separate switches - I'm sure I remember reading this in the manual somewhere but that was a long while ago.

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If that's the way it is, it ain't going to be changed now. If I had my machine available, it would be an easy test - set homing going and trigger a limit switch.

Quote:

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Originally Posted by cropwell

Anyway, My question is about homing and limits and I cannot find any reference to the query in the Mach3 reference manuals.

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So what's your question.?

Well this has been an interesting day! I think the moral has to be: If you've got the test gear, use it!!

I did some quick mods in line with previous suggestions but to no avail. I was soooooo confident as well.

I finally got the oscilloscope out and looked at the noise on the limit switch inputs to the board. Clean as a whistle until I enabled the motors. Then there are short bursts of a surprisingly sinusoidal 6MHz waveform. Same on the 5V power rail. Same on the 5V ground rail!! I thought all the earthing was OK, Could be better, but OK. Clearly the wiring to the sensors needs to be completely replaced. At the moment it's modded from what was there for the microswitches. Obviously not good enough.

Problem is at that frequency a 20cm length of earth wire is too long. I measured 400mV (peak-peak) across the two ends of a wire les than that length from the chassis to the 5V ground connection on the board. The real killer comes from switching on the mains to the VFD. There's a transient on the Z sensor input that goes from 4.5V to below zero. It only lasts about a tenth of a microsecond but that's long enough. Obviously I'm not switching the VFD mains on and off while the machine is in use but it indicates there's a problem in need of fixing.

I did take a squillion screen grabs of the waveforms to show off with but the fact is that the controller needs to be rebuilt with more care taken over the earthing and the sensor cabling needs to be replaced with a separate, unbroken screened cable from each sensor (existing unscreened cables cut short as advised earlier). I suspect some of the wiring and existing filtering attempts are ringing and I doubt that even the most expensive new control board could be relied upon to work faultlessly in this electrical environment, so I'll stick to my well used $20 unit for now, as well as the old computer and parallel interface. Perhaps a complete new machine will materialise once I've retired. Whenever that turns out be now that the world has turned upside down.

I now have to wait for RS to deliver the goodies required for the improvements so will have to try being patient for a few days. Maybe I should try designing that low cost DIY optical fibre interface that would allow the motor drivers to sit next to the motors and no long wires through the machine except power rails. Well we must keep the old brain busy during these long spells stuck at home. Does anyone know if the professionals have moved to fibre connections for motor controllers and/or limit switches? It would solve a lot of problems.

Quote:

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Originally Posted by Kitwn

Maybe I should try designing that low cost DIY optical fibre interface that would allow the motor drivers to sit next to the motors and no long wires through the machine except power rails. Well we must keep the old brain busy during these long spells stuck at home..

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The first time I attached a scope to my spindle encoder on the lathe my jaw hit the floor with the noise from the 3-phase motor, so I appreciate where you're coming from. I'm surprised you're seeing that behaviour on short cables though comms theory was never my strong point - I'll believe your experience over my memory any day. I still think using cheap (or expensive!) BoBs with opto-isolated inputs offers a lot of advantages, if only for the pathetic frequency response that will filter any amount of HF noise as well as providing much better noise immunity level than HC-series logic.

In my case (the spindle encoder) - the design of the 7i76e Mesa card is intelligent and offers a differential input for shaft encoders with 130R input, which allows easy connectivity to a RS485 driver to allow transmission over a balanced twisted pair - helped massively. I appreciate this doesn't work in your case.

Of course, most machines are massive lumps of cast iron and steel cabinets which form a good hard ground and provide a lot of shielding into the bargain. In contrast, if you are constructing a relatively spaced out router(?) using extruded sections with long lengths (high stray inductance), you lose many of those benefits.

For my machines, I've used Lapp Olflex shielded drag cables, which have shielded bundles within a shielded outer braid. I noticed that the original wiring in my Shizuoka (Matchmaker CNC system, using Parker hannefin servos etc) used simple screened multicore cables for stuff like the encoders but simple unscreened wires for most of the rest (limit switches, solenoids etc). The spindle motor and brushed servos were wired through flexible, grounded steel conduits, which would have contained a lot of the HF noise. I reused that system when I swapped out the electronics and it's been very well behaved.

I have the Yaskawa VFD in the same cabinet as the rest of the electronics but I bought the pukka Yaskawa-Schaffner EMC filter to go with it. I've not had any issues with that either.

Quote:

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Originally Posted by JAZZCNC

So what's your question.?

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Does Mach3 disable limits when homing, or is this an option? (post #25)

Quote:

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Originally Posted by JAZZCNC

You think it works well because you have nothing to compare it against.! When you get the new controller with higher pulse freq etc you'll see the difference.

Regards the N/O question then provided you use separate inputs then you can use different switch types. Obviously if wiring in series and sharing the same input they must all be the same type.

Also if your thinking to buy Warp9 ESS then I'd look at others like UC300 because they are better than ESS and you are not stuck with mach3/4.

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Thanks. There's eperate connections for estop and each axis limits. 2 switches will be wired in series per axis.

In regard to the controller in the u.k. I can easily get an ESS or a UC400eth but the 400 has limited ports.
I've found a UC300eth-5lpt in Ireland and that's about it.

I'll still end up using the cheap boards on them though but that shouldn't matter too much, should it.

Quote:

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Originally Posted by dazp1976

Thanks. There's eperate connections for estop and each axis limits. 2 switches will be wired in series per axis.

I'll still end up using the cheap boards on them though but that shouldn't matter too much, should it.

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As mentioned before make sure the "cheap" board has Inputs that are opto-isolated.