Proximity Sensor Wiring Issue? Help needed. - Page 5


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Thread: Proximity Sensor Wiring Issue? Help needed.

  1. #49
    Gold Member john-100's Avatar
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    Default Re: Proximity Sensor Wiring Issue? Help needed.

    not knowing the part numbers of the LED indicator and opto-isolator on the ESS board
    when the sensor is connected directly to the ESS
    I made the assumpion the voltage at the junction of the LED indicator and 330 ohm resistor will not change from the 2.69V I calculated earlier

    the 100 ohm resistor limits the current through the SN04N when it grounds the ESS input

    when the SN04N output is off the current flowing into the ESS board will drop about 0.55V across the 100 ohm resistor
    so the ESS input will be at about 4.455V.


    Proximity Sensor Wiring Issue? Help needed.-5v-npn-senso-100ohm-pullup-r-plus


    a quick calculation shows that when the SN04N sensor powered from a +5v supply
    a 100 ohm pull up resistor will also work when connected to a C25 board's input

    ( a 1000 ohm resistor will also work but using a 100 ohm resistor has the advantage of reducing the
    input impedance helping to reduce the effects of electrical noise picked up by the sensors wiring )

    Proximity Sensor Wiring Issue? Help needed.-5v-npn-sensor-plus-c25r3-input-jpg

    PS
    NPN open collector outputs can only pass current to ground and not supply current from the sensors positive supply

    ( sensors with PNP outputs can supply current from the positive supply but are not able to switch to the output to ground )

    john

    Last edited by john-100; 11-11-2018 at 09:04 AM. Reason: add PS NPN open collector outputs verse PNP opec collector outputs outputs


  2. #50
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    1# which software or app that you use to calculate for the right ohm?

    2# I also ordered this pnp-NC
    http://vi.vipr.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&item=381489388907&t=1527063981000&tid=10&category=57520&seller=mdflyelectronics&excSoj=1&excTrk=1&lsite=0&ittenable=false&domain=ebay.com&descgauge=1&cspheader=1&oneClk=1&secureDesc=0

    Which application good for homing npn-no, limit pnp-nc?
    Or homing pnp-NC, limit npn-no?



  3. #51
    Gold Member john-100's Avatar
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    Default Re: Proximity Sensor Wiring Issue? Help needed.

    2)
    after reparing various video , balanced audio and multiway camera cables experiance tells me
    the odds are higher that a sensor wiring fault will be a wire going open circuit

    so I would use a sensor with a normally closed output -
    the problem with N/O outputs you don't know a wire has broken and the control is not going to see the switch close

    in your case with the sensor connected to an ESS or C25 input
    use a sensor with an open collector PNP output

    when a N/C PNP sensor is connected to a 5V supply you don't need a resistor connect the ESS input to work
    ( but a 100 ohm resistor between the PNP output and the ESS input will limit the fault current if the ESS input is shorted to ground )



    you may find when connecting a N/C PNP sensor to the C25 input
    a 100 ohm pull down resistor may be needed between the ground and C25 input to reduce the input impedance and make the C25 less sensitive to stay pickup

    ( if you have a 100 ohm resistor in series withe the sensor output to limit the current if the output is shorted to ground
    then the pull down resistor if fitted will need to be about 270 ohms to ensure the 74HC14 input is at more than 3.5V when the sensor output is at +5V)


    1)

    I did not use any app to find the correct value of pull up resistor in my original diagrams

    using a mixture of experiance and reverse engineering the ESS and C25 inputs

    going by the chinese data I found for the SN04N sensor
    the maximum current the sensor can sink to ground is 200mA

    with a 100 ohm pull up resistor the SN04N sensor is going to sink 50mA that flows from +5V when the sensor NPN output is switched on
    the 100 ohm resistor only dissipates 0.25W

    the 74HC14 IC on the C25 board is a CMOS IC has a high impedance - the low impedance pullup resistor (100 ohms)
    will help to reduce any stray voltages picked up by the sensor wiring

    as an alternative
    using a 1800 ohm pullup will form a potential divider with the 4700 ohm resistor shown in the C25 manual

    result is the 74HC14 input will be at 3.6V when your sensors NPN open collector transistor is off

    I used 0 to 30% of the 5V supply as a valid low level logic = 0 to 1.5V
    and 70% to 100% of the 5V supply a a valid high logic level = 3.5 to 5V




    looking at the SN04N sensor being connected to the ESS input
    the diagram in the manual indicates 7mA will flow into the input through the 330 ohm resistor , passing through the LED indicator and the opto-isolators input LED

    using ohms law, 7mA through the 330 ohm resistor gives you 2,31V across the resistor
    subtracting 2.31 from 5V gives you across the two leds 2..69V

    adding the 100 ohm pull up resistor to 330 ohms gives you 430 ohms

    I assumed the volt drop across thetwo LED's will remain at 2,31V
    so dividing 2.69V by 430 gives you 6.25mA through the LED's instead of 7mA
    I do not think a reduction in current of about 10% will stop the circuit from working

    John

    Last edited by john-100; 11-11-2018 at 01:05 PM. Reason: correct some typos and recalculate for 1800 ohm C25 pullup


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Proximity Sensor Wiring Issue? Help needed.

Proximity Sensor Wiring Issue? Help needed.