· input devices:
Intelligence of an automated system is greatly depending on the ability of a plc to read in the signal from various types of automatic sensing and manual input field devices .push buttons , keypad and toggle switches which form the basic man-machine interface, are types of manual input device . On the other hand, for detection of work piece, monitoring of moving mechanism, checking on pressure and or liquid level and temperature and many others, the plc will have to tap the signal from the specific automatic sensing devices like proximity switch, limit switch, photoelectric sensors, level sensor, temperature sensor, and smoke sensor and so on. Types of input signal to the plc would be of ON/OFF logic or analogue these input signals are interfaced to plc through various types of plc input module.
Figure 1-6
· output devices :
An automatic system is incomplete and the plc system is virtually paralyzed means of interface to the field output devices. Some of the most commonly controlled devices are motors, solenoids, relays indicator, buzzer and etc. through activation of motors and solenoids the plc can control from a simple pick and place system to a much complex servo positioning system. These type of output devices are mechanism of an automated system and so its direct effect on the system performance.
However, other output devices such as the lamp, buzzers and alarms are merely meant for notifying purpose. Like input signal interfacing signal from output devices are interfaced to the plc through the wide range of plc output module.
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