The timer (T) in plc is equivalent to the energized time relay in the relay control system. It provides an infinite pair of normally open normally closed delay contacts. The timer has a set value register (one word length), a current value register (one word length) and a map register (a binary bit) for storing its output contacts. These three quantities use the same address. Numbering. However, the use is different and the meaning is different.
The timers in the FX2N series can be classified into general-purpose timers and integrated timers. They are timed by accumulating clock pulses of a certain period. The clock pulses have three periods of 1ms, 10ms, and 100ms, and the contacts operate when the count reaches the set value. The set value can be set with the constant K or the contents of the data register D.
1. General purpose timer
The general-purpose timer is characterized by the fact that it does not have a power-down hold function, that is, the timer is reset when the input circuit is disconnected or powered off. The general-purpose timer has two types of 100ms and 10ms general-purpose timers.
(1) 100ms general-purpose timer (T0~T199) A total of 200 points, of which T192~T199 are sub-programs and interrupt service program-specific timers. This type of timer is a cumulative count of 100ms clock, the set value is 1 ~ 32767, so its timing range is 0.1 ~ 3276.7s.
(2) A total of 46 points for the 10ms general-purpose timer (T200 to T245). This type of timer is a cumulative count of 10ms clock, the set value is 1 ~ 32767, so the timing range is 0.01 ~ 327.67s.
The following is an example of how a general-purpose timer works. As shown in Figure 1, when the input X0 is turned on, the timer T200 counts up the 10ms clock pulse from 0. When the count value is equal to the set value K123, the timer is normally turned on and Y0 is turned on. It is 123 × 0.01 s = 1.23 s. When X0 is turned off, the timer is reset, the count value becomes 0, its normally open contact is open, and Y0 is also turned OFF. If the external power supply is de-energized, the timer will also be reset.
Figure 1 General-purpose timer works
2. Totalizer
The integrated timer has the function of counting accumulation. If the power is turned off or the timer coil is OFF during the timing, the integrated timer will keep the current count value (current value), and continue to accumulate after power-on or timer coil ON, that is, its current value has a hold function, only the integrated calculation When the timer is reset, the current value becomes 0.
(1) The 1ms integration timer (T246 to T249) is a total of 4 points, which is the cumulative counting of 1ms clock pulses. The timing time range is 0.001 to 32.767s.
(2) The 100ms integration timer (T250 to T255) has a total of 6 points, and the time range for accumulating the count of 100 ms clock pulses is 0.1 to 3276.7 s.
The following is an example of how the integrated timer works. As shown in FIG. 2, when X0 is turned on, the T253 current value counter starts to accumulate the number of clock pulses of 100 ms. When X0 is turned off after t0, and T253 has not counted to the set value K345, the current value of the count is retained. When X0 is turned on again, T253 continues to accumulate from the current value of the hold. After the time t1, when the current value reaches K345, the contact of the timer acts. The accumulated time is t0 + t1 = 0.1 × 345 = 34.5 s. When the reset input X1 is turned on, the timer is reset, the current value becomes 0, and the contact also follows the reset.
Figure 2 The working principle of the integrated timer
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