3500/15 each circuit is very important, the requirements must be quickly and accurately determine the point of failure when the first option is better; in general, the third option is better, due to the classification of the fault alarm display, you can directly determine the nature of the fault, to know the impact on the equipment or industrial process, you can take immediate measures to deal with it, and then in combination with other phenomena, factors, another set of or At the same time, in combination with other phenomena, factors, another group or several groups of alarm conditions, the specific fault point will be divided from such.

The 3500/15 has LEDs to help check whether a fault has been caused by an external device. Whether in the simulation debugging or practical applications, if a system circuit can not act in accordance with the requirements, you should first check whether the PLC input switch electrical contact point is reliable (generally by viewing the input LED indicator or direct measurement of the input), if the input signal fails to transfer to the PLC, you should go to check the input corresponding to the external circuit;