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Ten years of PLC veteran field experience

Last Updated on 2018-07-09 Hits:2248

Ten years of PLC veteran field experience


A younger brother who has been engaged in the automation career for nearly a decade has found that the ability and level of work of engineers on-site commissioning is the most critical factor for the success or failure of a project. However, many engineers lacked the necessary psychological preparation and technical preparation before they rushed to the scene to perform their duties. Therefore, they could not exert their abilities after arriving at the scene. So here are some of my own experiences, I hope to have some inspiration for all technical engineers.
First, preparation before departure
Those who are engaged in the technical support of PLC, if they want to go to the site to start the system debugging, whether it is for the OEM customer or the system integration of a process control, we must do some preparatory work in advance. Just like a "friend" before going out, you have to change your own clothing, especially shoes, bring water, food, and some self-defense supplies in the wild. If it is overnight, you must have a tent, a flashlight, etc. as a profession. PLC technical support engineers, there are also a lot of things to be prepared.
First of all, you have to arrange your own itinerary plan and food, clothing and accommodation. If you need accommodation, then how to set up a ticket, hotel (hotel, guest house), here is not much to say. If the time is long (such as more than one month), in order to save money, you should consider renting a house in the local area, especially when starting a group rather than a person. These problems are the same as ordinary travel, although these issues have the same impact on your mission as your professional level. Imagine that you are on the scene, because food poisoning causes a week of dysentery to affect the work, you know that you should prepare those things. Usually, the administrative department of an experienced automation company will consider these situations for the engineers, but as an engineer, you must confirm it to see if everything has been arranged.
After you have settled in the food, clothing, and housing, you must prepare your own tools. As a field commissioning engineer for PLC, it does not require a lot of debugging tools. However, a screwdriver and a multimeter are still necessary. In addition, if you want to coordinate the system with the on-site instrumentation sensor, there is also a signal generator to simulate the signal of the field instrument to determine that the signal on the site is intact when a problem occurs. Also, a rugged laptop is a must-have tool for programming and debugging. Although these tools you can ask the user to prepare, but as a professional PLC engineer, if you do not have these tools, you will be suspected of your professional level. Some other instruments, if you need, you can ask the company or customer to prepare them in advance, such as oscilloscopes, regulated power supplies, and so on. After all, these less versatile instruments are usually not portable or spare.
There are some small things that are often overlooked, and you must be useful after you have prepared them. For example, electrical tape, heat shrink tubing, lighter (naturally, if you smoke, no one else will have it), cable tie, and if the field wiring is completed, prepare some cables with the same signal cable. , and some screws that fix the base. You may suspect that you need to do this. Believe me, bring these, although some are worth only a few cents, but when you get to the scene, you may save you a day or even a few days, especially if you go to a remote place. The time of the mountains. Although the manufacturers have screws at the time of delivery, anything can happen at the scene. If the screws are not enough (and this is inevitable every time), it will cause many problems.
In addition to the above, it is the spare parts to be taken for this commissioning. Although the on-site cargo list may have considered the issue of spare parts, in order to cope with the situation, you may want to carry some spare parts yourself. The first is the PLC substrate (some become a rack), power supply, CPU module, because these are the basis of a PLC can work, if there is only one system in the field, then there is only one of these modules, if there is no backup, once In the event of a breakdown, all your work must stop. So it is best to bring a set.
Other I/O modules and communication modules, if there is only one on site, you should consider taking one more. For those who already have more than two modules on site, you don't have to think about bringing them.
Second, the design of the work


If the system is large, the limitations of the remote unit, the number of local racks, and the number of modules per rack are not due to system functionality and technical limitations, but due to the use of normative restrictions. When configuring the system hardware, consider the combination of these modules.
For the configuration of the power module, a senior engineer should be able to make a reasonable match. For example, power modules usually have 5A and 10A respectively. If there are fewer modules, you can use power modules with low power. If there are many modules, you should use high-power power modules. In general, if the field instrument requires the PLC to supply 24V DC power instead of the external power supply (such as RTU), it is usually reasonable to use a high-power power supply in the rack where the CPU is located.
In addition, when I/O modules are installed, modules of the same model are usually placed together according to different systems. However, if the output module and the input module form a loop, it is reasonable to place the modules involved in the parameters of one loop on a rack (or a rack controlled by a CPU). Some designers don't consider this when designing, you can adjust it.
In the selection, because various PLCs have large, medium and small, these are mainly caused by the different performance of the CPU module. In fact, not necessarily a large function is appropriate. In addition to the price considerations, the main reason is that if the number of control points is small and the small CPU module is fully capable, the small CPU will be more reliable than the large CPU module. Because small CPUs involve less resources, and large CPUs have more resources. In the execution of the program, in order to process resources that are not needed by those programs, time is also allocated to deal with them, which not only causes waste of resources, but may In the program processing, the small CPU can work more simply and stably.
In the process of designing the bottom, it is important to note that for any changes in the design, you can only make suggestions, not arbitrarily. Because your job is to follow the design, not the design, so you can give advice on anything that you find unreasonable, but you must wait until the design change confirmation is in your hands before you can follow the changes. After the design work, although this change may be your opinion. Also, even if the original design is what you did, you should notify the customer after the change and obtain the written consent of the customer.
Third, the installation steps
After arriving at the site, before installing the system, you need to consider whether the installation environment meets the requirements of the PLC environment. You can refer to the manuals of various products. However, no matter what kind of PLC, it can not be installed in the following places: places with corrosive gases, places where sunlight directly shines, places where the temperature changes up and down in a short time, where oil, water, and chemicals are easily invaded. Where there is a lot of dust, the vibration is large and the mounting parts are displaced.
If it is necessary to use it in the above environment, it is necessary to make a suitable control box for the PLC, using the specifications and necessary protective measures. If you need to use it in the wild at very low temperatures, you can use a control box with heating function. How to make these protective boxes or control boxes, manufacturers and qualified system integrators will provide customers with the appropriate supply and design.
When using the control box, pay attention to the following items in the position where the OpenPLC is installed in the control box: whether the air circulation in the control box is smooth (the appropriate distance must be maintained between the devices), and whether the transformer, motor controller, inverter, etc. are kept with the PLC. Appropriate distance, whether the power line and the signal control line are separated and configured, whether the position of the component is suitable for future maintenance, whether space is reserved for future expansion of the system.
In addition to the above considerations, there are other considerations to be aware of.
The first important thing is the isolation of static electricity. Static electricity is an invisible killer, but it may be overlooked because many people are not at risk. In the northern, dry places of China, static electricity on the human body is a factor that causes static electricity to damage electronic components. Although you are hit by static electricity, it is only a slight numbness, but it is fatal to the PLC and any other electronic devices.
There are three ways to avoid static shock: when repairing or replacing components, touch the grounded metal to remove static electricity from the body; do not touch the connector or IC pin on the circuit board; electronic components are not When using, use the package with isolated static electricity to place the components inside. Imagine that the components in the PLC are a delicate baby, and those static electricity will cause the baby to die, and it will be easier for you to treat the problem with the right attitude.
When the base is installed (RACK), after determining the various control components and slot positions in the control box, the hole position should be calibrated according to the dimensions shown in the drawing. After drilling, tighten the fixing screws until the base is secure. Before installing the power supply module, you must also pay attention to whether the grounding end of the power cable is connected to the metal chassis. If not, it must be connected. If the grounding is not good, it will lead to a series of problems, such as static electricity, surge, external interference, and so on. Because the PLC is not grounded, the PLC can work. Therefore, many engineers with less experience mistakenly believe that grounding is not so important. It's like climbing a cable without a protective cable. Although you don't have any effect when you move forward normally, once you lose it, without the rope, your life is over. The grounding of the PLC is equivalent to protecting the cable from the PLC.
When installing an I/O module, pay attention to the following items: Before inserting the I/O module into the slot on the rack, make sure that the module is a pre-designed module; the I/O module is inserted into the rack. When inserting the groove, be sure to insert it all the way to ensure that the contact points are tightly coupled; the module fixing screws must be locked; after the terminal block is inserted, the upper and lower screws must be tightened. Due to the influence of transformers and motors on site, there will be some vibration. If these screws are loose, the module will be released from the rack.

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