Tag Archives: plc timer

Power failure delay type time relay physical wiring diagram

It is mainly used on equipment that needs to be stopped for a certain period of time after power failure. In many cases, it is necessary to use a power-off delay type relay for control. For example, it is necessary to control a motor, and it is required to restart the work after pressing the stop button for a certain period of time, then a power-off delay relay is needed to achieve the above functions.

The time relay is a controller whose delay function is realized by an electronic circuit. According to the control occasion, you can choose to use: power-on delay type A; power-off delay type F; star-delta delay type Y; power-on delay type C with instantaneous output; interval delay type G; reciprocating delay type R ; Disconnect the delay signal type K and other specifications to meet the required control occasions.

Time control programming example implemented by Mitsubishi PLC with timer and counter

Time control programming example

The timer of the Mitsubishi plc FX series is a power-on delay timer. Its working principle is that after the timer coil is energized, the delay starts, the time is up, the contact action; when the timer coil is powered off, the timer The contact is instantly reset.

However, in practical applications, we often encounter control requirements such as power-off delay, time-limited control, and long delay, which can be achieved through programming.

1, power-on delay control

The delay on control program is shown in Figure 3-27. The control function it realizes is that after X1 is turned on 5, Y0 has output.

The working principle is analyzed as follows:

When X1 is in the 0N state, the coil of the auxiliary relay M0 is turned on, and its normally open contact is closed and self-locking, so that the coil of the timer T0 can be kept in the power state.

After the coil of T0 is turned on for 5 s, the current value of T0 is equal to the set value, the normally open contact of T0 is closed, and the coil of output relay Y0 is turned on.

When X2 is in the ON state, the coil of the auxiliary relay M0 is turned off, the timer T0 is reset, and the normally open contact of T0 is turned off, so that the coil of the output relay Y0 is turned off.

2, power failure delay control

The delay off control program is shown in Figure 3-28. The control function it implements is that the output stops working after the input signal is disconnected for 10s.

The working principle is analyzed as follows:

When X0 is in the ON state, the coil of the auxiliary relay M0 is turned on, its normally open contact is closed, and the coil of the output relay Y3 is turned on. However, the coil of timer T0 will not be energized (because its front () is off).

When X0 changes from ON to OFF, () is in the on state, and timer T0 starts counting. After l0s, the normally closed contact of T0 is opened, the coil of M0 is de-energized, and the output relay Y0 is disconnected.

3, limited time control

In actual engineering, it is often encountered to limit the working time of the load to a specified time. This can be achieved by the program shown in the figure, which implements the control function of controlling the maximum working time of the load as l0s.

The program can achieve the minimum working time to control the load. The control function implemented by this program is that the minimum working time of the output signal Y2 is 10s.

4, long delay control program

In the PLC, the timer’s timing is limited, the maximum is 3276.7s, less than lh. To achieve longer timing, you can use two or more timer cascades, or use a timer with a counter, or use a counter with a clock pulse.

(1) Timer cascade use

When the timer is used in cascade, its total timing is the sum of the time set by each timer.

Figure Use two timers to complete the 1.5h timing. When the timing is up, Y0 is powered.

(2) Combination of timer and counter

The timing of 1h is completed with a timer and a counter.

When X0 is turned on, M0 is powered and self-locked, and timer T0 generates a pulse sequence with a period of 100s by itself resetting as a count pulse of counter C0. When the counter has 36 pulses, its normally open contact closes, causing output Y0 to turn on. From X0 to Y0, the delay time is 100s x 36 = 3600s, which is 1h.

(3) Combination of two counters

Figure 3-33 shows the timing of 1h with two counters.

M8013 (1s clock pulse) is used as the count pulse of counter C0. When X0 is turned on, counter C0 starts counting.

After 60 pulses (60 s) have been counted, its normally open contact C0 sends a count pulse to counter C1 and resets counter c0.

The counter C1 counts the c0 pulse. When 60 pulses are counted, the normally open contact of C1 is closed, and the output Y0 is turned on. From X0 to Y0, the timing is 60s x 60 = 3600s, which is 1h.

5, boot cumulative time control program

The PLC running cumulative time control circuit can be used in combination with M8000, M8013 and counter to compile the display circuit of seconds, minutes, hours, days and years. Here, you need to use the power-off type counter (C100~C199), so that the accumulated time of each power-on can be timed, as shown in the figure.

What is the function of a PLC timers

PLC timers

PLC timers is a function that we often use when programming with PLC. In programming applications, we can often use timer to realize delay start function and alarm protection function. Moreover, the use of the timer is similar to the time relay in the relay control circuit, so it is easy to use, but is such a simple application, can you use it well?

Let’s take a look at a program. This is a program sent to me by a student. He did a marquee program while practicing programming. He chose a 10ms timer to do it, but found that the marquee program does not execute. Ask me what is the reason? The program is as follows:

This is a very simple program, but it is such a simple program. When the ROL_B instruction is not executed at the time of execution, then where does the problem occur? Can you see what is the reason? What should I do? .

In fact, this situation is mainly due to the use of the timer, the understanding of the timer refresh mode is unclear, the S7-200 series PLC has three resolution timers, each resolution of the timer, its refresh The way is different. So what is the refresh of the timer? Personal understanding is the update of the current value of the timer.

The 1ms timer refreshes the timer every 1ms. The 10ms timer is the refresh of the timer at the beginning of each scan cycle. The refresh of the two resolution timers has nothing to do with the program scan of the PLC. In the case of a 100ms timer, it is refreshed each time a timer instruction is executed.

Cause Analysis:

The 10ms timer is used in this program. Then, the 10ms timer and this program are taken as an example to explain why the following ROL_B instruction is not executed. As shown, we divide the program into three parts, a, b, and c.


a is the start of the scan of the PLC program. The program uses a 10ms timer, then the PLC refreshes the current value of the timer at a, assuming that the current value of the refreshed timer is exactly equal to 10. When the program is executed to b, if M0.0 is ON. We know that the operation of the on-delay timer is when the current value of the timer is equal to the set, the contact of the timer is activated, and the current value of the timer is reset to 0 when the driving condition of the timer is turned off. Therefore, the T33 normally closed contact here is to be operated (because the current value of the timer has been updated at a, and the updated value is equal to 10 equal to the preset value of the timer), then The driving condition of the timer is turned off and the timer is reset to 0. When the program executes to c, because the current value of the timer is equal to 0, the T33 contact above the instruction is not closed, so the following ROL_B instruction is not executed.

Solution:

(1) Replace the 10ms timer with a 100ms resolution timer, because the 100ms resolution timer is to be refreshed when the program executes to the timer command.

(2) Refer to an intermediate variable, and the program is changed as shown below to ensure that the timer is reset after the ROL_B instruction is executed first.