Need simple circuit to convert NPN output to 2 PNP output

yctiew

Member
Join Date
Sep 2003
Posts
2
I'm new in this forum. Currently, i have one sensor with power supply DC24V (NPN output). But the PLC i using only allow PNP input. At the same time this sensor need to give signal to 2 channel in the PLC. Anyone that can show me the simple circuit to convert 1 NPN output into 2 PNP output?
 
Use a pull-up resistor

If you connect a pull-up resistor between the +24 volt supply and the sensor output, you can connect the sensor to a sinking (PNP) input. However, there are a few things to be aware of.

When the sensor output is "on" (connected to 24 volt common), the PLC input will be "off" (zero input). If necessary, this can usually be inverted in the PLC logic.

When the sensor output is "off" (sensor output open), the PLC input will not see a full 24 volts. Having 2 inputs in parallel will give a lower voltage than 1 input. Usually a 24 volt PLC Input will operate down to 10 or 12 volts so check the PLC specs.

The value of the pull-up resistor is critical. If the resistance is too high, the PLC input voltage will not be high enough to turn the input on. If the resistance is too low, you will overload the sensor output. As I don't know the specs of the sensor or PLC you are using, I will give you an example of sizing the resistor to the minimum resistance value for a typical sensor.

Typical sensor max. output current = 200 mA
Minimum resistor value = 24 volts/.2 amps = 120 ohms
Resistor Wattage = 24 volts x .2 amps = 4.8 watts

From experience, I would say that this value should allow you to drive 2 Inputs on most PLCs. Connect the sensor and resistor to the PLC and turn off the sensor output. Measure the PLC Input voltage and confirm it is more than the minimum voltage needed to turn on the input.

Good Luck
 
Hello!
Put a auxillary relay in the system it's easy and cheap.
Why do you need the same input to two places, you have a PLC just transfer the input to a memory-bit and use it as much as you want!
 
Thank you for the reply. Unfortunately, my application is involed high speed signal. Relay may not fast enough to response. I need one sensor to send signal to two different PLC. High speed sinal.
 
Cross-connecting a sourcing output to a sourcing input or a sinking output to a sinking input is another question that comes up frequently. Take a look here .

This should work fine for two PLC inputs. With two parallel inputs, the net resistance is halved, so the current is doubled. Choose the wattage of your resistors accordingly.
 

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