Wiring 24v NPN Proximity Switch to 5v BOB - Why does'nt it work

[cropwell]

For those who mentioned the possible 10K resistor in the switch - the BOB appears to have a current-limiting resistor in series with the input to the buffer inverter which also includes clamp diodes to restrict input voltage at the input pin. So the 10K resistor, if it does exist, is just going to act as another pull-up when the switch is open and can be ignored when the switch is closed. If it doesn't exist, it doesn't matter as the BOB has an onboard pull-up anyway.

Don't know the zener voltage (zen, zener, zenest), but here's the essentials of the internal circuit.

Now I am going to get ANOTHER Brandy !!!!

[Neale]

Thanks for that, Rob - first time I've seen a representation of the switch internal circuit. I find those little extracts of both input and output circuits very useful in getting an understanding of how things go together, and especially when it comes to working out why something doesn't work! Too much detail for some, perhaps...

Now I'll have to draw out the combined circuit of four of those (NC versions) strung in series, so that I can use a single input for combined limit switches, just to reassure myself that it should work - even though I've wired it up on the bench and it does seem to.

Maybe some of us take a more theoretical approach where others just want to know where to stick the black wire

Just in case the OP is still with us and hasn't given up the will to live - this just confirms that your original wiring should be fine if you take out the resistor.

[Clive S]

Now I'll have to draw out the combined circuit of four of those (NC versions) strung in series, so that I can use a single input for combined limit switches, just to reassure myself that it should work - even though I've wired it up on the bench and it does seem to.

Not sure but I recon they will be ok for limits but if used as home combined.
I think there will be an increasing delay put in to the circuit the more you connect.

[Neale]

Couple of points there. Personally (and without looking up switch data sheets to see if they quote switching times) I suspect that compared with typical machine speeds, any delay will be insignificant (*). That's based on gut feel rather than hard data, though. Second point is that I would be more concerned about repeatability than actual switching time. I don't really care if the response time is, say, 100uS as long as it is always 100uS, so that the machine always stops in the same place. Doing a bit of my usual back-of-the-envelope sums, I reckon that at full tilt my ballscrews will be turning at 1000rpm. Say, 17rps. 800u steps per rev, so 13600 steps/sec. That's about 75uS per step. In practice, final homing is done at, say, 10% of that, so as long as the switch responds repeatedly to the nearest 3-400uS, you should be able to stop at the same ustep. Dean's demo of homing repeatability using proximity switches a while back supports this.

(*) what probably matters more is that you always home at the same speed as I suspect that exact switching points will depend on speed of approach to target but that is something that's under our control. It only matters for homing anyway; don't really care exactly where the machine stops if it hits a limit as long as it stops before something gets broken!

[cropwell]

I think there will be an increasing delay put in to the circuit the more you connect.

Apart from the inductive sensing circuit, I see no capacitative or inductive components that will introduce any time elements into the switching circuit. Sorry for the delay in replying

[Clive S]

Apart from the inductive sensing circuit, I see no capacitative or inductive components that will introduce any time elements into the switching circuit. Sorry for the delay in replying

I was looking through this- http://www.ab.com/en/epub/catalogs/1...23/Wiring.html

It states "response time is equal to the response time of the first sensor plus the sum of the turn on times of the others. "

But all this has been killed to death many times. Can't beat having each sensor on its own pin.

[cropwell]

I was looking through this- http://www.ab.com/en/epub/catalogs/1...23/Wiring.html

It states "response time is equal to the response time of the first sensor plus the sum of the turn on times of the others. "

But all this has been killed to death many times. Can't beat having each sensor on its own pin.

This only seems to apply for two wire sensors in series. Three wire sensors in parallel won't be affected. Phew: our 'homes' are secure, we can all sleep safely in our machine beds this afternoon.



Rob

[Boyan Silyavski]

Ok. Now that io have you here :-) , i have another quick question . If BOB has transformer that powers limit switches and at the same time spindle speed output, and you connect a couple of limit switches in series and find that spindle speed output does not work right. Then could you add additional transformer positive and negative to the BOB outputs, same 12V vdc, but from another supply , so you kind of "help " it?????????

[MikeyC38]

Thanks for that, Rob - first time I've seen a representation of the switch internal circuit. I find those little extracts of both input and output circuits very useful in getting an understanding of how things go together, and especially when it comes to working out why something doesn't work! Too much detail for some, perhaps...

Now I'll have to draw out the combined circuit of four of those (NC versions) strung in series, so that I can use a single input for combined limit switches, just to reassure myself that it should work - even though I've wired it up on the bench and it does seem to.

Maybe some of us take a more theoretical approach where others just want to know where to stick the black wire

Just in case the OP is still with us and hasn't given up the will to live - this just confirms that your original wiring should be fine if you take out the resistor.

Hi Neale - I'm still here! Just about. But I must be having a brain fade because when I connect the black wire to pin 10, the blue wire to the pin 10 GND, then run a wire back to the -ve 24v supply it buzzes and does'nt work. I checked the GNDS on the ZP5A-INT board (it has a 5v supply from my Leadshine PS408/5 ), all the gnds are connected by doing a continuity check with the BOB unpowered from the -5v pin. I guess I just need to sleep on this and start again tomorrow. I must be missing something in what you guys have said and suffering from a case of "Goldfish brain"

[m_c]

I hope you mean +ve and not -ve.
.
Best to go back to basics, wire up just the power and gnd to the sensor, and use a multimeter to check that the output is switching. Provided that works, connect it to the BOB.