How to just calculate high-end PLC? - - - - - -

What kind of PLC can be regarded as high-end PLC?

reliability? Stability? Information security? What is the most need to consider the future of our high-end PLC controller?

let's together to discuss!

the first example industrial field information collection and communication management PLC

we know that the industrial site there are two kinds of measurement and control system. Category is called the production process control system, hereinafter referred to as DCS; Category is called the power equipment and power measurement and control system, called the SCADA.

such as an industrial site has a water pump. Monitor and control the parameters such as flow, pressure of the pump belongs to the category of the DCS. Most of the current measurement and control parameters using inverter to perform. The parameters of the DCS monitoring frequency converter to upload information and real-time release control command to the frequency converter; To drag the pumps high pressure working parameters of the motor itself, as well as a variety of power supply switch electrical appliances, the measurement and control is belong to the SCADA.

production process parameter change is relatively slow, and interference is weaker. Such as flow, temperature, pressure, material and so on, its cycles of changes for a second, or even longer. Electric power measurement and control of process parameter change fast, strong. Such as switch electrical opening and closing, peak voltage mutation, impact current mutation and short circuit current and so on. In the process, change cycles are usually shorter than 1 second, even shorter than 5 milliseconds.

SCADA and DCS, PLC in the field have ark, the purpose is to collect information, and carry out the tasks of communication management and information exchange.

I work belongs to the SCADA, we will be supporting the communication management machine at the scene. Start general PLC, we use the results found that the problem, and focused on the problem such as memory allocation, communication interrupt processing program, sometimes even automatically reset to restart, to bring huge disruptive impact on the site.

in addition, the PLC level of EMC is particularly important. Many low-end PLC, in the industrial field, especially in high electromagnetic environment in substations, and even damaged and spontaneous combustion.

so, under the condition of this kind of work, must adopt a mid-range PLC. This kind of PLC communication interface and communication rate should be enough, the power of the immunity ability will be enough.

second example

for each redundancy system

so-called for redundancy, refers to the two PLC CPU work at the same time, a master to use, a backup. Once the main CPU crashes, spare CPU must be seamless switching.

this kind of measurement and control PLC used in the rotor of the generator.

the frequency of the alternating current is 50 hz is known to all, it is conceivable that the generator rotor speed how fast. Perform measurement and control of PLC, if once appear CPU crashes, it must be in a few clock cycles by spare CPU is replaced.

this kind of double CPU PLC controller belongs to high-grade PLC, also called a PLC hardware redundancy.

PLC software redundancy, it can work under the environment of low speed. Such as ABB for the station transformer room in the subway engineering ( Distribution of power supply transformer room, environmental control, traction substation) Form a complete set of PLC redundancy is commonly software redundancy. Even if it's slower, but must also be the mid-range of PLC.

, we see in these two examples using what grade of PLC, entirely by the working characteristics of control object and its working environment. Has nothing to do with the design engineer hobbies.

therefore, review and determine a certain type of PLC, not only to look from its sample parameters, but also look at its type testing parameters, especially the EMC performance, system stability and reliability.

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