Generally in manufacturing units
push buttons are commonly used in switching on or off the devices. Push buttons
have one inherent characteristic that they cannot retain their position i.e.
one has to constantly press the push button in order that the machine gets and
remains started. Moreover, if this condition is not met the device with
constantly flicker causing damage to the machine.
Toggle switches are another
option which can be used for this purpose. The main advantage with them is that
they can retain their position which the push buttons could not do. Toggle
switches need to be operated in order to change their position. Thus we can
turn on the switch and rest assured that the machine is working. But this
causes a problem in industries, as the same switch will have to be operated
again in order to switch off the machine. Logically with the help of ladder
logic it will not be switched off.
In order to remove the
disadvantage of pushbutton a solution internally in the ladder logic in PLC has
been given in the form of instruction by many manufacturers of PLC. This is
latch and unlatch or set and reset instruction.
No comments:
Post a Comment