If the resistance value is too low a high current will flow through the pull up resistor heating the device and using up an unnecessary amount of power when the switch is closed. Lets give it 12 v to make the maths easier. Oops Pnp Npn Help Please Plcs Net Interactive Q A Choosing Between Line Driver Open Collector And Push Pull Working Of Pull Up And Pull Down Resistors With Examples It must be connected between supply and signal and signal to plc inputimage attached plc input 24ma at 15vdc supply 24vdc. Pull up resistor plc input . Assuming that you are using a current sinking input the best way to do this would be to use a converter unit or industrial opto isolator but using a pull up resistor is not uncommon. The first factor is power dissipation. The values in the calculation below came from the plc spec in another question i answered. Th...
