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https://www.vishay.com/docs/83741/83741.pdf example 2

I have existing H22A2 optocouplers that I am trying to run 12vdc through to get a plc input to turn on and off. I am using a 1k resistor on the 5vdc LED. I am using a 2.7k resistor on the OPTOTRANSISTOR side with the 12vdc. I can get the input to turn on and off, but the voltage drop is so minimal that it is way to sensitive to be consistent. Any ideas?

plc model from automation direct BX-DM1E-18ED13 specs https://cdn.automationdirect.com/static/specs/bxdm1e_18ed13.pdf

H22A2 datasheet https://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/H22A1,2,3.pdf

I will have 4 of the optos going to 4 separate inputs.

'>9.0vdc ON <2.0vdc OFF for inputs

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Welcome to EE.SE. (1) There is a schematic editor built in to the editor toolbar. Post a schematic of your actual circuit. (2) What do you mean by "emitter"? This usually refers to the transistor pin with the arrow on it. If you are referring to the LED you will cause a lot of confusion. (3) You should also embed the Example 2 image in your post so we all don't have to follow links. (4) Finally, add the make and model of your PLC and a link to the datasheet. \$\endgroup\$ – Transistor Nov 20 '17 at 20:50
  • \$\begingroup\$ Sorry, first post. \$\endgroup\$ – Kurt Nov 20 '17 at 21:19
  • \$\begingroup\$ Hi, @Kurt. A month later and you are still having trouble with this. You do not need to use a pull-up. Did you wire as shown in Figure 5 of my answer? \$\endgroup\$ – Transistor Dec 20 '17 at 16:54
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Your question is quite unclear but I suspect that you think that the PLC requires a pull-up or pull-down resistor as shown in the Example 2 of your link. This is not the case.

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1.

The PLC input can be connected directly to ground in the case of a current-sourcing type or directly to positive supply in the case of a current-sinking type. Typically about 10 mA will flow and ensure adequate illumination of the internal opto-coupler which isolates the inputs from the internal logic.

For your circuit you wire the opto-isolator's transistor as shown depending on input type.

The current-sinking type of input is often called a PNP input as it would work with PNP-type three-wire industrial sensors. Since you are using a "two-wire" opto-transistor the NPN transistor works in both configurations.


Update after links posted.

enter image description here

Figure 2. The PLC accepts sinking, sourcing or AC configuration.

That means that there are back-to-back diodes or a rectifier on the inputs.

schematic

simulate this circuit

Figure 3. Options for interfacing your opto-switch.

Choose (a) or (b) to suit other switches in the system.


Update 2:

schematic

simulate this circuit

Figure 4. Redrawn OP's schematic.

Corrected version of your schematic is above. Note that this is the same as I drew in Figure 3b.

enter image description here

Figure 5. Correct schematic with current path highlighted.

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  • \$\begingroup\$ BRX plc from automationdirect. Model BX-DM1E-18ED13. I have a 5vdc power supply going through a 1k resistor to the LED. The optotransistor side I have 12vdc in order to be able to turn ON the input. (10-24vdc required). \$\endgroup\$ – Kurt Nov 20 '17 at 21:29
  • \$\begingroup\$ You're asking too much of those you hope will help you. Please post a link to the datasheet for the device in question - not the catalog page. \$\endgroup\$ – Transistor Nov 20 '17 at 21:37
  • \$\begingroup\$ media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/… \$\endgroup\$ – Kurt Nov 20 '17 at 22:07
  • \$\begingroup\$ I think I am not driving the LED bright enough. I did get it to work with a multimeter. Able to pull 12v down to almost zero before blowing the LED. \$\endgroup\$ – Kurt Nov 20 '17 at 22:09
  • \$\begingroup\$ Sorry, I can't help further until you address the points I numbered in my comment under your question. I was looking for the datasheet for the PLC. Put all the required information in your question - not scattered through the comments. \$\endgroup\$ – Transistor Nov 20 '17 at 22:11

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