How can we calculate the maximum hard wire cable length for : 1- Digital I/O's . 2--Analogue I/O 's . for our PLC 's M340 ,Premium and Quantum Ranges and is there any tool to calculate the length ?
The length of the 4-20 field wiring for the Analog module is really dependant on a few things. Normally its not only 4-20 but others too. Just if I take below example then
1) The analog card does not supply the current for the loop. This is done by an external supply or the transmitter itself. Depends on the sensor types like 2-wire or 4 wired externally powered types.
2) The resistance of the wire itself.
The longer the cable the higher the resistance.
As per the formula's , the resistance of a cable is directly proportional to its length and inverse proportional to the diameter.
R = l x ρ / A
R : electrical resistance
l : conductor length
ρ : specific resistance
A : conductor cross section
If you want to send the signal over long range, the transmitter will have to spend more energy to keep the current in the correct range, since the cable resistance is such a high value. You could increase the diameter - there by reducing the cable resistance - or contact the transmitter manufacturer to determine how much power the transmitter is able to transmit.
As you know the module reads 4-20 milliamps. The source needs to be able to push that amount of current across the field wiring and the load resisters at each end of the loop. At the receiving end means Analog input card just ensure that there is not much voltage drop due to resistance of cable. The supply must be capable of driving the loop. That said, Ohms law dictates the rest.