Analysis of Common Problems of Mitsubishi Timers and Counters

1. I want to use the normally open contacts of the timer in 20 places in the program. Is that ok? If the timer reaches the set time, will these 20 normally open contacts act together?

A: Yes, because the contact of the timer (normally open or normally closed) is a programming soft element. It can be used an unlimited number of times in the program. It is equivalent to having unlimited contacts for you to use. These 20 contacts do not act together. The PLC program runs by scanning line by line. When the line is scanned, the contacts of that line will act. Therefore, strictly speaking, these 20 contacts have limited actions and do not act together.

2. The book says that the timer only has power-on delay contacts. What should I do if I want to use power-off delay contacts?

Answer: The timer only has power-on delay contacts. If you want to use power-off delay contacts, you can only do so by programming a power-off delay program. The figure below is a power-off delay disconnection program for reference.

3. I saw T5 D100 in someone else's program, but I don't understand what the timing setting value of this T5 is?

Answer: The timer setting value of timer T5 D100 is the value of data register D100. This is an indirect setting method for timer timing. The advantage of indirect setting is that as long as the value of D100 is changed, the timer setting value is changed.

4. What does the current value of a timer refer to? What is the use of the current value?

A: When the timer is driven to start timing, its value changes from 0 to the set value. This constantly changing value is called the current value of the timer. The current value provides the user with a timer function, that is, in conjunction with the contact comparison instruction, the output can be controlled at any time point within the set value range.

5. How to improve the timing accuracy of the timer?

A: Timers are divided into three types according to the counting clock: 100ms, 10ms and 1ms. The difference between them is that the timing program is different. The 100ms timer changes according to the 0.1s program, while the 1ms timer changes according to the 0.001s program. If you want to improve the accuracy of the timer, choose a 1ms timer.

6. What are the three elements of a timer?

Answer: The three elements of a timer refer to the start, contact action and reset of the timer.

7. I have never understood why T192-T199 timers are used in subroutines? Can't other timers be used?

A: In a subroutine, you can use either a common timer or a subroutine-specific timer T192-T199. The difference between the two is that a common timer only counts when a subroutine is executed. If the subroutine is not executed, the timing will be interrupted. This affects the accuracy of the timing and causes timing errors. However, T192-T199 will not do this. If a special timer is started in a subroutine, the timer will continue to count even if the subroutine is not executed, thus ensuring the accuracy of the timing.

8. What is an accumulative timer? What is the difference between it and a general timer?

A: The accumulative timer is also called the power-off holding timer. The difference between this and the general timer is that during the timing process, if the driving condition is disconnected or the power is off, the accumulative timer can maintain the current timing value. When the driving condition is connected or the power is on, the timing will continue on the basis of the original timing until the timing reaches the set value.

9. Teacher, could you please give me a detailed introduction on how to reset the timer?

A: The timer reset is different according to its reset method. For general timers, its start and reset are determined by the driving conditions. When the driving condition changes from guide to reset, the timer is reset immediately. In addition, when the PLC is powered off, the timer is automatically reset. For the cumulative timer, it is not reset due to the disconnection of the driving condition or power failure, and must be reset using the RST instruction. Of course, ordinary timers can also be reset using the RST instruction.

10. Is the timing setting value of timer T5 K10 10S?

A: The timing setting value of the timer is the setting value multiplied by the clock pulse period of the timer's clock pulse. The clock pulse period of timers with different addresses is different. All timers are divided into three clock pulse periods: 100ms, 10ms and 1ms. The same setting value, but different timing setting values ​​due to different addresses, for example:

T5 k10 timing time is 1s

T243 K10 timing time is 0.1s

T275 K10 timing time is 0.01s

The relationship between timer addressing and clock pulse period can be found in the data or manual

11. In a ladder diagram program, how is the current value of the timer represented?

A: In the program, the current value of the timer appears as the operand of the function instruction. It is represented by the address of the timer. For example:

RST 248 Reset the current value of timer T248

MOV T10 D0 transfers the current value of timer T10 to D0

12. What changes occur to the timer after resetting it?

Answer: Timer reset mainly produces the following actions.

1. The current value of the timer becomes 0

2. The contacts of the timer return to their original state (i.e. normally open to normally open, normally closed to normally closed)

13. I would like to ask you, when the timer reaches the set value, if the driving condition is still met, will the timer continue to count?

A: When the timer reaches the set value, if the driving condition is still met, the current value of the timer will not change and the set value will remain unchanged. The timer will not continue to count. Wait for the timer to reset.

14. Why does the timer T0 K40000 fail to input an input error?

Answer: The timer setting value register is a 16-bit data register, and its maximum value is K32767. K40000 has exceeded this maximum value, so it cannot be entered into the ladder diagram.

15. Teacher, what is the timing setting value of T0 K-500?

Answer: The timing value of the timer cannot be set to a negative value. If it is set to a negative value, its timing time is set to 0 seconds.