1. Some of these proximity switches already have a pull-up resistor inside.
Here is a good explanation of how to calculate it's value.
See page 11 http://cnc4pc.com/Tech_Docs/C50R1_user_manual.pdf in the ones I have it is 10K

..Clive

2. Hi Graeme, HankMcSpank,

OK, that makes a bit more sense now, thank you. I'll check Hank's suggestion first - power it up without the resistor between black and brown and check the voltage on the black. If it is nothing then I have a simple switch and can follow up on your suggestions Graeme. I may need to clarify something with you but lets see what I have first.

If it is 24V then I have a pull-resistor inside the sensor and need to do something else as I know this board won't like 24V into the logic circuits!

I see Clive has posted as well so I'll have a read of his link next . . .

Thank you

3. If there is a voltage on the black, then a simple voltage divider should do....but it'd be useful for you to measure the input resistance of the follow on BOB board input pin (as that will end up being in parallel with your proposed voltage divider)....I'd imagine it'll be very high input resistance on your BOB input.
Last edited by HankMcSpank; 24-05-2015 at 07:48 PM.

4. Originally Posted by HankMcSpank
If there is a voltage on the black, then a simple voltage divider should do....but it'd be useful for you to measure the input resistance of the follow on BOB board input pin (as that will end up being in parallel with your proposed voltage divider)....I'd imagine it'll be very high input resistance on your BOB input.
Checked the black wire without resistor and it was 12V (running from 12V supply for now) which means there is a resistor in the sensor and I can't wire it as a simple switch. Used method Clive posted and worked out the value as around 5k ohm

So I can work out the other resistor required to complete the divider except I need to factor in the Bob resistor

Tried to check Bob resistance across pins with multimeter (board was off) and got no reading at all. What is the method to determine this resistance
Last edited by routercnc; 25-05-2015 at 03:02 PM.

5. Originally Posted by routercnc
Checked the black wire without resistor and it was 12V (running from 12V supply for now) which means there is a resistor in the sensor and I can't wire it as a simple switch. Used method Clive posted and worked out the value as around 5k ohm

So I can work out the other resistor required to complete the divider except I need to factor in the Bob resistor

Tried to check Bob resistance across pins with multimeter (board was off) and got no reading at all. What is the method to determine this resistance
As mentioned, the BOB input resistance will likely be high ...there's nothing special involved with the measuring method - just check for resistance between the BOB input pin & BOB ground ...powered off is fine. (if you get too high a reading for your meter to detect, then to all intents & purposes the BOB input resistance can be disregarded for the purposes of your 'to be deployed' voltage divider)

What supply voltage do you eventually intend running your sensor with?
Last edited by HankMcSpank; 25-05-2015 at 03:18 PM.

6. I had the meter on max setting and still got no reading

Final system will be 24V when PSU arrives - testing on 12V for now

7. OK

If the internal R is 5K then the most current that can flow at 12 V will be 2.4mA. Just to prove this put the meter in series with the black wire to gnd and check (put the meter on to the mA range). I am sure that I used one of these sensors connected to the 5V input of my bob. But don't let the magic smoke out. ..Clive

8. I was just about to suggest trying to establish what value the internal R is (on the sensor)....try connecting a 4.7k resistor between your sensor's black wire & your supply voltage ground ...power up the sensor & measure what voltage you have across the 4.7K resistor (it doesn't have to be a 4.7k resistor ...whatever resistor you have to hand!)
Last edited by HankMcSpank; 25-05-2015 at 04:38 PM.

9. Small update. Thanks for all your help on the proximity switches. I think I have a plan on that now but will revisit that later because . . .

24V PSU, 2off 24V relays, and the 20A contactor all arrived in the post today! Big thanks to Dean for some behind the scenes help .

Managed to get a quick hour in the garage tonight and made some progress:

24V PSU wired in
Contactor to control the linear power supply mostly wired in (need the 24V DC feed to complete)
Shifted all the earth blocks to a common location to make proper star-earth point
Made new earth cables to suit
Added terminal end block clamps to stop them wobbling around
Swapped out one of the 12V relays for the new 24V, but not wired in. Got one more to do.
Added 2 pairs of green adapter brackets (near the VFD) - these will guide the power and signal cable (not added yet). Not really required but they were about £1.30 for 2 on ebay and I just liked the look of them !

Overview:

AC DIN rail coming along:

DC DIN rail getting close (ignore 12V labels it will be 24V):

Questions on the contactor:
T1, T2 are the mains input ?
L1, L2 are the switched output ?
Should I keep the earth permanently connected (i.e. not through T3/L3 of contactor) ?
A1 / A2 24V DC polarity important? I'm guessing not.
There is a 0 / 1 switch in the middle - some sort of tester / over-ride? Can I leave it at 0 ?
Last edited by routercnc; 29-05-2015 at 10:01 PM.

10. Originally Posted by routercnc
Questions on the contactor:
T1, T2 are the mains input ?
L1, L2 are the switched output ?
Yes Either or doesn't matter really it's just a switch.

Originally Posted by routercnc
Should I keep the earth permanently connected (i.e. not through T3/L3 of contactor) ?
Yes leave Earth unbroken.

Originally Posted by routercnc
A1 / A2 24V DC polarity important? I'm guessing not.
Yes it matters. A1 is Positive A2 Negative.

Originally Posted by routercnc
There is a 0 / 1 switch in the middle - some sort of tester / over-ride? Can I leave it at 0 ?
It's not a switch it's a Lever. The Contactor can have a Module added onto front and this switches it. Look inside the Box it came in and you'll see what i mean.?

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