Timeline for Confusion with NPN input wiring to a converter
Current License: CC BY-SA 3.0
7 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Sep 3, 2017 at 15:32 | comment | added | Bruce Abbott | ni.com/white-paper/3546/en , electronicdesign.com/power/… | |
| Sep 3, 2017 at 15:22 | comment | added | user1245 | What is the advantage of isolating the device's ground from the converter's? Thanks | |
| Aug 31, 2017 at 20:43 | comment | added | user1245 | Thanks I tried NPN. Please see my edit at the end of my question I added the whole diagram with my interface, I made an interface and tested as shown. The only thing I dont know when the transistor is ON, Y1 is directly grounded and how much current can flow. What I dont know is the output impedance the value of R4. I made a test and when I measure Y1 this way scope shows 0-10V pulses at the point Y1 so I adjusted R4 in simulation to have the same result. I didnt get any malfunction besides the ripple in analogue output of the converter. WHat do you think about my interface in my edit? | |
| Aug 31, 2017 at 19:59 | comment | added | Bruce Abbott | You still need an interface with PNP because the voltage levels (PNP/NAMUR: High > 5V Low < 2,5V) are not compatible. Also you still need an opto-coupler if the device does not have isolated output (if in doubt, include it!). The circuit for PNP is the same as NPN, except that you connect Q1 Collector to Y2 and Emitter to Y3. The only reason for having a PNP input is to support sensors which have PNP output, switching to + (Y2) rather than - (Y0). Since the optocoupler output is floating it doesn't matter which input you choose. | |
| Aug 31, 2017 at 19:35 | comment | added | Bruce Abbott | In your circuit the total resistance is 330+560 = 890 Ohms. If this drops 5V then the current is 5V/890 Ohms = 5.6mA. To get lower voltage you need less resistance. 330 Ohms would drop 330 Ohms * 5.6mA = 1.85V, which is safely below 5V. 330 Ohms matches the switch resistance in your diagram, but up to ~500 Ohms total resistance should be OK. | |
| Aug 31, 2017 at 8:14 | comment | added | user1245 | Thanks but couple of questions: 1) You wrote "except that your external resistance must be too high"; but in your example your external resistor is 330 Ohm less than mine. Do you mean to make the voltage at Y1 less than 5V the external resistor(R2 in your diagram) should be many kOhms? I dont get why.. 2) Do I also need an extra interface if I instead use PNP input for a device with 0-5V pulse output?(I would be so glad if you can add the PNP wiring to your answer) | |
| Aug 31, 2017 at 2:34 | history | answered | Bruce Abbott | CC BY-SA 3.0 |