Mitsubishi MELSEC-F FX-TRN-BEG-E, User Manual

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FX-TRN-BEG-E B: Let’s Study the Basics 2
B-15
2.1.3 Points of Training and Control Specifications
1) Inputs, outputs and other devices
The PLC is equipped with input points and output points which are connected to control
equipment and a variety of devices the aid in sequencing operations.
- What are devices?
Control equipment such as switches and lamps are connected to the PLC and symbols
such as X, Y, M, T and C are asssigned as their names. Each symbol represents a
different function and has a serial number to identify it.
Symbols and numbers handled inside the PLC are device symbols and device numbers,
most times these are generally called devices.
Input: From X000
Inputs are terminals to receive signals from external equipment (such as switches and
sensors) and their device symbol is represented by “X”.
Numbers are assigned starting from ’000’.
Output: From Y000
Outputs are terminals to drive external equipment (such as lamps and motors) and their
device symbol is represented by “Y”.
Numbers are assigned starting from ’000’.
Auxiliary relay: From M0
Auxiliary relays (which are also called internal relays) are provided inside the PLC and their
device symbol is represented by “M”.
Auxiliary relays are convenient when using dual OUT instructions and two or more contacts
at a time. (Refer to the explanation in Section 3).
Timer: From T0
Timers are provided inside the PLC and their device symbol is represented by “T”. Timers
are used provide a set period of delay time before their nominated contacts are either
opened or closed depending upon the program instructions.
Timers will be studied in the exercises in the category ‘C: Step-up’.
Counter: From C0
Counters are provided inside the PLC and their device symbol is represented by “C”.
Counters are used to increment or decrement in steps of one to a preset value and
subsequently open or close their nominated contacts depending on the program
instructions.
Counters will be studied in the exercises in the category ‘C: Step-up’.
- Device number and number of devices
Inputs (X) and outputs (Y) are expressed in octal - X000 to X007, X010 to X017 (and so
on), Y000 to Y007, Y010 to Y017 (and so on).
Auxiliary relays (M), timers (T) and couners (C) are expressed in decimal - M0 to M10,
M11, M12 (and so on).
The number of devices available varies depending on the PLC. For the number of
available devices in the virtual PLC, refer to the appendix.