long distance encoder signal


Thread Starter

J-F Portala

Hi lister,

Can I use encoder signal on a 30m distance, or is it necessary to protect it and how?

I want to use the same encoder signal for 3 PLC (accepts 0-24V pulses) and a PC board which only accepts (0-5V)

Can I share the encoder signal in 4 and use a resistor divider to transform 24V to 5V.

It seems to be too simple to work correctly.

Do I have to separate signals or amplify it.

Do you know some device which could help me.

Thank your
J-F Portala
[email protected]

hisham el- beltagy

it is not a good idea you must use a splitter for this and a converter to transform the 24V to 5v
i recommand PEPPERL & FUCHS devices they are very reliable.

Hakan Ozevin

We shared the encoder signal to 3 PLC inputs from a 40m distance and it did worked.
Theoretically you can do all you have mentioned, but it all depends on the output impedance of the encoder and the input impedance of your board.
You have to either check it on site or better, test it on a circuit which simulates your equipment.
Firstly if you want to use any encoder over particularly long distances or in particularly noisy(electrical noise) environments then there are a number of things to consider :-
1/ The maximum frequency that the encoder will generate ( this is (the expected RPM/60) times the pulses per rev. The answer is the pulses per second or frequency. The higher it gets & the longer the cable the more critical the chosen method of output drive of the encoder becomes.
2/ At the time of purchase most encoder manufacturers give you a choice of outputs i.e. TTL, Totem pole, Open collector/ line driver. They also give you a choice of "complimentary" outputs i.e. A + (compliment of A) & B + ( Compliment of B).
3/ The best combination is to choose an encoder with :-
- Complimentary "totem pole" or "line driver" outputs
- try to use the highest voltage output possible. This will improve the signal to noise ratio so that interfering signal levels must be higher before they begin to have any detrimental affect.
- use low capacitance shielded cable. The higher the capacitance per unit length of the cable the more it degrades the signal from the encoder
particularly at higher pulse frequencies.
- have a receiving device which has "line receiver" type inputs that accept the
"complimentary outputs" from your encoder.
- Configure the receiver device to "Quadrature count" this will make it more noise immune i.e. electrical "fizzing" on one edge will not cause the counter to increment.

I know the above will not benefit you if you're already stuck with your encoder & receiver. However, the principles still apply i.e.
-"TTL" output is the worst
-"Open collector" output is next best but you will have to have "pull up" resistors fitted at the receiver end. The values of these resistors should be as low as the open collector device can drive.
-"Totem pole/Line driver" is the best.
- Always choose low capacitance shielded cables, this will yield benefits for any configuration.
- at the receiver, configure for "quadrature" count.
Good luck! Ken :)