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10
Timer Application Practice: A Decade of Workshop Experience from an Old Electrician
A few days ago, Xiao Zhang rushed to me: “Master Li, please help me check, the conveyor belt on production line three keeps stopping and starting, causing us to rework a large batch of products!” I followed him to take a look, and the problem was with the timer settings in the control cabinet. After adjusting a few parameters, the production line immediately returned to normal. Xiao Zhang looked at me in admiration: “How did you find the problem so quickly?”
When it comes to timers, many young workers find them complicated, but that’s not the case. The timer is the ‘metronome’ of industrial equipment, and once you master it, you have grasped the ‘heartbeat’ of automated devices. Today, I will share with you the experiences I have accumulated over more than a decade, without holding anything back.
1
Microcontroller Timers: The Soul of Industrial Control
Microcontroller timers may look sophisticated, but they operate on principles similar to those of our everyday alarm clocks. I remember one night when I was urgently repairing a filling line; it was because the timer interrupt handling was not written correctly that the conveyor belt kept stopping and starting.
You must be curious: why are timers so important?
“Xiao Wang, factory equipment requires precise time control, just like you need to master the heat when cooking. If the heat is too high, the pot burns; if it’s too low, the food won’t cook, which delays production, right?”
The core of the microcontroller timer is the interrupt and the counter; once you understand these two, you can solve 80% of the problems. For example, if we want an LED to blink once per second, the key part of the code is these few lines:
void Timer0_Init(){TMOD = 0x01; // Set timer modeTH0 = 0x3C; // Set initial timer valueTL0 = 0xB0; // 50ms timer valueET0 = 1; // Enable timer interruptTR0 = 1; // Start timer}
Beginners often stumble on calculating timer values. Don’t memorize formulas; remember this little trick: Under a 12MHz crystal oscillator, a 50ms timer value is 0x3CB0. This is much more practical than those complicated formulas!
PLC
PLC Timers: The ‘Time Manager’ in the Workshop
PLC timers are different from microcontroller timers; they are more like a ‘foolproof’ electronic clock. Last month, Director Wang’s injection molding machine had a problem because the PLC timer for the mold temperature machine was set incorrectly, resulting in insufficient cooling time and product deformation.
There are mainly three types of PLC timers: On-Delay (TON), Off-Delay (TOF), and Pulse (TP). The most common mistake I have seen is confusing TON and TOF.
“Remember, On-Delay is like boiling an egg; the timer starts counting as soon as it is activated, and only outputs when the time is up; Off-Delay is like a microwave; after pressing the stop button, it continues to work for a while.”
Taking Siemens S7-200 as an example, a simple delay control ladder diagram is just these few lines:
|–| |—————————-(TON T37)—–|| I0.0 | PT=300 ||–| |————————————-(Q0.0)-|| T37 |
Many technicians do not understand how PLC timers work internally, which is like walking with their eyes closed; when encountering a fault, they are left dumbfounded. In fact, the PLC timer is essentially a counting and accumulating process; the system has a basic scanning cycle (usually a few to dozens of milliseconds), and each scan adds a little to the current value of the timer.
2
Practical Experience in Timer Applications
Anyone can talk theory; let me share some practical experiences from the field.
First, always add delay protection when starting equipment. Last year, the pressure machine in workshop two failed because it did not have a startup delay, causing the hydraulic pressure to not be fully established before starting, resulting in damage to the hydraulic cylinder and delaying production for a week.
Second, cascading timers can achieve complex control logic. For example, if a packaging line needs to delay the conveyor belt for 2 seconds before starting, and then delay 5 seconds to start boxing, using two cascaded timers can easily achieve this without complex programming.
Third, remember to back up your timer parameters! I have seen too many cases where parameters that were painstakingly adjusted were lost due to sudden power outages or misoperations. Now I have developed the habit of taking a photo with my phone to record the adjusted parameters immediately.
3
Master Li’s Practical Advice
Finally, here are three pieces of advice for young people:
1. When debugging timers, start with a larger value to confirm the logic is correct before making precise adjustments.
2. If possible, use an oscilloscope or a multimeter with a timing function to measure the actual delay; do not completely trust theoretical values.
3. The industrial environment is complex; critical equipment must have a watchdog timer to prevent the program from running away.
Remember, learning timer applications is not difficult; the challenge is to combine theory with practical experience. Don’t just read books; go to the field to work with the equipment, and when you encounter problems, ask the experienced workers. Soon, you will be able to handle things on your own!
