Hardware 3.5 Digital inputs The inputs pick up the digital signals of a variety of sour- ces. They connect to the device by screw-type locking ter- minals ( а illustrations in chapter 3.2). Make sure that they work within the switching thresholds indicated below, which particularly applies to proximity switches and semi- conductor sensors. The input circuitry adapts the incoming signals to the system voltage. Ш Defined signals and switching thresholds Logical 0 ≤ 5 V Logical 1 ≥ 15 V (Hysteresis 1...4 V) Ш Signal delay Peak voltages (noise impulses) are filtered to avoid them being considered as valid signals which might trip unintended switching actions.
This delays signal detec- tion by rated 5 ms: U [V] 24 Raising delay: t ve = 3.0...7.0 ms 15 Falling delay: t va = 4.0...7.0 ms 5 t[ms ] S ignal t ve tva 1 0 Fig. 7: Input signal delay Input signals are read between program cycles and writ- ten into the process image . To calculate the average availability of signals to the user program, you must there- fore add the program cycle time to the specified delays. 28