Hollysys PLC – PLC programming advice

(1) When the PLC and the host computer (or touch screen) form a monitoring system, there are many times when there are "manual", "automatic" and other control modes on the screen (generally when there is only one multiple). You can use the "MOV" command in the program. For example, when "Manual" is selected, the constant 1 MOV will be placed in one register VB10, and when "Auto" is selected, 2 MOV will be placed in the same register VB10. As long as you judge how much data is in the register, you know what kind of control the system is. The advantage of such an idea is that it is easy to understand and does not require troublesome procedures such as interlocks.

(2) When the program has analog control, if the read analog quantity is basically error-free, the time filter can be adopted to delay the time for a period of time. If the error of the read data is large, other filtering methods are required, such as averaging. Relevant information can be consulted.

(3) In the process of program debugging (especially when the equipment is transformed, when your program is added to the program of the original equipment), when the conditions are met in the program statement, and the output coil is not connected, you can check whether your program is between such statements, such as JUMPgo to and other statements. There is also a possibility that after interrupting the program, the conditions are met and the output is not connected, and generally the program in this section is not scanned.

(4) In the sequence control program, that is, after the completion of one action, enter the next action, and other similar sequence control, using +10+10 control mode, I think it is very convenient. The idea is: preset a register, the value is 0 at the time of initialization, when the system starts, +10 to it, the register is 10, and the register is equal to 10 when the first action can be made; After the first action is completed, then +10 to the register, at this time the register is equal to 20, you can do the second action, and after the second action is completed, +10, at this time the register is equal to 30, so that as long as you judge how much data in the register is, you know to complete the action. When you need to jump, you can no longer +10, you can add +20+30...., depending on the actual need.

Why add 10 instead of 1, because after adding 10, if you insert a paragraph, you just need to choose a random position in these 10 free places.

(5) When designing the program, when there is a process failure (non-control system control), it is best to keep the fault phenomenon and have a light and sound alarm. Until the operator resets to let him know that the system is faulty. Otherwise, there will be downtime, and others will think that your program is a problem. These are generally the things to keep in mind when designing a new system.

(6) For frequently called subroutines, they can be made into submodules and called frequently.

(7) because the production machinery in the work cycle of each step movement in the execution of a certain amount of time, and these times have a certain limit, so these times can be taken as a reference, at the same time that the step action to be detected begins, start a timer, the time setting value of the timer is 20%-30% longer than the time that the action is to last under normal circumstances, and the output signal of the timer can be used for alarm or automatic shutdown device. When the time of a certain step action of the production machinery exceeds the specified time, reaches the corresponding timer preset time, and has not yet been transferred to the next step action, the timer sends a fault signal, the signal stops the normal work cycle program, starts the alarm or stops the program, which is what we often call overbeat protection.

(8) Some safety detection switches (such as emergency stop buttons, safety light curtains, limit switches, etc.) use normally closed (NC) inputs.

(9) For the sake of safety and energy saving, try to design the output to act only when it is needed, and stop the output once it is in place, instead of designing it to output all the time, and disconnect the output when it needs to be stopped.

(10) The action principle of the actuator should be that it is better not to move than to move!

(11) Single equipment control: a single device must have soft hand operation/automatic switching and soft manual operation can start/stop function, from automatic switching to soft manual operation, the equipment can not be stopped; When switching from soft manual operation to automatic, the device start/stop depends on the automatic program.

(12) A single equipment (pump, fan and other large equipment) must be rotated after 24 hours of operation, and there must be a cumulative running time, except for the start/stop sequence set by the upper computer, the operator sets it by himself.

Hollysys PLC – PLC programming advice

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