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Author Topic: Proximity Sensors, do they need to drop to zero volts when triggered ?  (Read 2356 times)

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Hello all...

Just received the following NPN DC6-36V Proximity Sensors, and im waiting for the following router to be delivered (so i can not test the switchs with the unit).

Right now im playing with the switchs using a bench power supply and they are working with 5v IN but when they are triggered, they only drop to 0.633v, not 0 volts, will this be a problem ?

Testing now with 12v (from bench power supply) to 5v voltage regulator.
Powering switchs with (brown wire) 4.978v from L7805 regulator
Not triggered, output (black wire) = 4.973
Triggered output (black wire) = 0.633



Secondary question(s) :-)

1) Would it make sence to use an exturnal power source (a "wall wart") hooked to a 5v voltage regulater, since the switchs are working at 5v ?
Knowing nothing about the control box (BOB) which comes with this router (aside from its an import), im trying to plan ahead so i have as little problems down the road.

2) Alittle electronic nieveness here...
I plan on using 6 switch, two for each axis.
Again, not knowing what the BOB with this router can do, would it make sence to wire three switchs in series (one per axis for the limits) and the other three by themselves for home (through reading on this board, thats seams pretty commen) to use less I/O pins ?
But... while testing two switchs in series:
5v power to (switch one) brown, then (switch one) black to (switch two) brown, there is a 2.5 voltage drop (so im gonna assume these switchs have some kind of resistors in them).
2a) So with that said, if i wanted to wire those three in "series" (more so, wire them so they only take up/use a single I/O pin on the BOB) could i run three to a relay (with resistors) and then have the relay hooked to a single pin (passing 5v through relay, then when one of the switchs triggers it will kill the power to the relay coil) ?


Thanks for any guidence.


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~ What was once an Opinion, became a Fact, to be later proven Wrong ~
2a) So with that said, if i wanted to wire those three in "series" (more so, wire them so they only take up/use a single I/O pin on the BOB) could i run three to a relay (with resistors) and then have the relay hooked to a single pin (passing 5v through relay, then when one of the switchs triggers it will kill the power to the relay coil) ?

2a) Just tested with two switches again:
Tied all Browns together (powering from 5v L7805 regulator)
Tied all Blues to negative
Tied all Blacks together.

Tested the output of the (tied) Blacks, and when ether switch is triggered it will drop to 0.650, so it looks like i could just do that and use a single I/O, right :-) ?
« Last Edit: April 20, 2016, 06:49:34 PM by iMisspell »
~ What was once an Opinion, became a Fact, to be later proven Wrong ~
They won't drop to zero, but what you need to remember is you are measuring them with a high impedance voltmeter.... Normally they will feed into an optoisolator running at around 10 to 20 mA, what I would suggest is maybe parallel running some resistors as sometimes the parasitic current of the sensors can be quite high, this will aide in sinking the current and lowering the voltage when in the low state.

I'd suggest searching Google for
Proximity sensor parasitic current as omcron did a few good PDFs discussing the issue and what to do.... It is more of an issue where you parallel run prox sensors together that are normally open (your application sounds normally closed)

I have 8 sensors in parallel, 7 are normally open, one normally closed (as it breaks when the axis moves too far), and a number of 2k resistors in parallel as they are 1/2 watt, running at 24volt.
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”
Oh yeah, all the prox sensors I've seen are rated at 6-36v.... They can be problematic outside of these ranges....follow the  manufacturer datasheet, as it stops nuisance tripping / false triggering plus the current requirements too.

Good luck
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”

Online Davek0974

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I would opt for a 12v supply - these are NPN so they drop to low level when triggered, the different voltages from sensors to BOB will not matter as only the grounds are tied. They do not need to drop to zero as logic levels for high and low are well defined and are rarely 0v and supply v.

You can do this with 3 sensors for all six positions - limits and homes. Just make the switch move towards two fixed targets - I have this on my mill and it really simplifies wiring etc, also less to go wrong, just think backwards - moving switch, fixed target ;)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives
This is an interesting bit of information on what is a low and a high signal in digital (TTL = Transistor, Transistor Logic) etc.

http://www.interfacebus.com/voltage_threshold.html

Basically a low will be anything below 0.8V (at the input), and a high anything above 2.0V (again at the input),

With the threshold voltage being ~ 1.5V before changing state.

Bit more info on your sensors here:
https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwiM_4nJ2Z_MAhXGWxoKHXoPBJgQFggiMAE&url=http%3A%2F%2Fwiki.fablab-muenchen.de%2Fdownload%2Fattachments%2F16091720%2FLJ8A3.pdf%3Fversion%3D1%26modificationDate%3D1446209248000%26api%3Dv2&usg=AFQjCNHFKdB2GAEV_pzktVMbEtx90q8hpw&sig2=x1mbBa1ui3y1Saf6KgkSoA

This was also a good read of info too
http://www.ab.com/en/epub/catalogs/12772/6543185/12041221/12041227/Parallel-Connected-Sensors.html
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”
Thanks for the info guys.

Gonna go the 12v route, have a wall power pack, but gonna try and get a computer power supple from a friend, would be nice to have 12, 5 and 3.5v all in one place in case ever needed.

robertspark, thanks for the time and research. I check out the links, some is alittle over my head right now, but i will go back and read more.


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~ What was once an Opinion, became a Fact, to be later proven Wrong ~