DCS系統DSMB179 57360001-MS模塊的操作DSMB 179
Relay Circuits The input/output points of the FA-M3 are normally connected directly to external devices. Relays, however, should be placed between the input/output points of the controller and the external devices in the following cases: - The controller is far away from the external devices and is susceptible to noise interferences in the field. - The controller is to be connected to devices that will generate high-voltage noise. - There is a need to clarify the relationship between other control lines with regards to the responsibility of handling respective signals. - A manually operated circuit needs to be included as a backup against failure of the I/O equipment.
Interlocking An interlock circuit is required when you handle particular outputs, such as those for the forward and reverse rotation of a motor that must not turn on at the same time. In such a case, installing an external interlock circuit allows one of the “b” contacts of the two relay coils to cut off the other when energized. Figure A3.13 shows an example of an interlock circuit.
Protection against Output Short-circuit
If any of the loads connected to the output terminals of the FA-M3 are short-circuited, an excess short-circuit current flows and there is the possibility that the external wiring will burn or there will be a generation of abnormal heat. It is therefore common practice to install fuses in the output circuits to ensure safety in the case of short-circuited loads and minimize damage to the FA-M3. Use of external fuses is recommended, especially for output modules that do not have built-in fuses or short-circuit protectors. Figure A3.12 is an example of an FA-M3 that is equipped with output short-circuit protection fuses. Note that these fuses are not intended to protect internal output elements against possible damage. In addition, these fuses may fail to blow in failure modes other than short-circuited loads.The power supply block of the FA-M3 incorporates a built-in power sequence circuit which prevents the system from malfunctioning when a momentary power failure or voltage reduction occurs. This system has two modes of detecting power failures; one is the standard mode and the other is the immediate detection mode. There are restrictions on the use of the immediate detection mode, as summarized in the table given below, according to the type of power supply module or CPU module used. The default (factory setting) mode is the standard mode.