Electric heating boilers are widely used, especially in schools, hotels, dormitories and shopping malls in the north. Electric heating boilers are widely used for heating and heating. Programming control of electric heating boiler by programmable controller can greatly enhance the control degree of each link in the working process of electric heating boiler and form strong protection for related components. In this paper, the basic connotation of electric heating boiler is briefly introduced, and the application of programmable controller is analyzed in combination with the actual situation, in order to improve the programmable control of electric heating boiler.
Electrically heated boilers have many advantages, which ensure their application in many fields. Traditional electric heating boilers are mainly controlled by contactors, relays and other components, which not only have a single function, but also some components are easily damaged, and have certain defects in control and reliability. Therefore, using programmable controller to program and control the electric heating boiler can greatly improve the performance of the electric heating circuit. Electric heating tube is the core component of electric heating boiler. Generally, according to the different capacity of the boiler, the number of groups selected by the electric heating tube is also different. The common range is between 10 groups and 20 groups.
Electric heating tube can work independently, that is to say, during the operation of electric heating boiler, electric heating tube can be increased or decreased according to different needs. For example, 20 sets of electric heating pipes were used, but with the decrease of heating demand, they can be reduced to more than ten sets of electric heating pipes.
Because there are some electric heating tubes which are not put into use, in the actual use of electric heating boilers, the electric heating tubes should be controlled by the controller to ensure that the running time of each electric heating tube is basically equal, so as to avoid the problem of a long running time of an electric heating tube. The requirement of cycle control urges the construction of control system to consider three aspects. First, the control system can monitor the water temperature of the outlet pipe in real time and control it according to the actual demand. When the water temperature approaches or reaches the upper limit, part of the electric heating pipe should be removed or the operation of the electric heating boiler should be stopped; when the water temperature approaches or reaches the lower limit, part of the electric heating pipe should be added to make the boiler run normally. Secondly, the control system can monitor and control the water temperature of the backwater pipe in real time. The basic control requirements are basically consistent with the water temperature control of the outlet pipe.
Thirdly, the control system can monitor the water pressure of the outlet and return pipes in real time and control the water pressure. When the outlet water pressure approaches or reaches the upper limit, stop the boiler operation. When the outlet water pressure approaches or exceeds the lower limit, the control circuit should be disconnected; when the return water pressure exceeds the upper limit, the supplementary pump should be stopped immediately. When the backwater pressure is lower than the lower limit value, the supplementary pump should be started to make up the water. In addition, the control system also needs to have the function of monitoring and alarming for under-voltage, over-pressure and phase-gap faults, so that relevant personnel can deal with these problems in time and ensure the safe operation of electric heating boilers.
Usually, according to the operation conditions and basic control requirements of electric heating boilers, Siemens S7-200 series of main engine modules can be mainly used. The commonly used main engine modules are CPU226 and S7-216. On the basis of the host module, a complete control system of electric heating boiler can be constructed by configuring two analog input module EM231, thermostatic element one digital input and output module EM223 and the human-machine interface TD200 according to the actual situation. In the whole control circuit system, CPU226 host module generally has 8K byte program memory and 2.
5K byte data storage. CPU226 is one of the largest input and output contacts of PLC in the host module of Siemens series. CPU226 has 256 timers and 256 counters.
The operation time is only 0.8? S. The interrupt processing function is very high speed. The analog input module EM231 can directly connect with the sensor, and can accept voltage source to form three different types of analog input. The digital input and output module EM223 can be used as an extension module of the host module CPU226, and can provide additional input and output points for the control circuit.
TD200 human-machine interface is designed by Siemens for S7-200 series main engine module. It is very simple and convenient to operate.
It can set system parameters through this interface, and display data such as outlet temperature of electric heating boiler.
In the host module of S7-200 series, the related program can be programmed by ladder diagram language. The program should have more perfect functional modules, which can complete counting, timing, calculation, PID operation and comparative analysis and other functions. The programming ability is very strong, and user debugging is also very convenient. In practice, ladder diagram programming starts from the beginning, then initializes the system, sets the operating parameters of the system, and then collects the analog data to determine whether the water temperature exceeds the maximum value, stops the boiler and gives an alarm if it exceeds the maximum value, and if it does not exceed the maximum value, judges whether the water temperature exceeds the median value. If it exceeds the median value, some heating tubes need to be removed or added.
If it does not exceed the median value, it is necessary to judge whether the boiler is short of water. If the boiler is short of water, it is necessary to stop the operation of the boiler and give an alarm. If the boiler is not short of water, it is necessary to judge whether the system needs to stop urgently. If an emergency stop is required, the boiler is stopped and an alarm is issued. If no emergency stop is required, the program is terminated. According to the above process, the programmable control system of electric heating boilers is very superior in the actual application process, which can be embodied in three aspects. First, the regulation and control of water temperature is more rapid.
Compared with the traditional relay control, the programmable control system is faster and faster in collecting, analyzing and controlling water temperature through sensors, and can complete the regulation and control of water temperature in a very short time. Secondly, the protection of the electric heating tube is more in place. Traditional control methods lead to deviations in the use of electric heating tubes. Some electric heating tubes are used for a long time and some electric heating tubes are used for a short time, which does not form a reasonable recycling control. But through the programmable logic controller, the cycle control of the electric heating pipe is realized. The electric heating pipe can be recycled according to the actual demand, which greatly improves the service life and efficiency of the electric heating pipe. Thirdly, the reliability is higher and the faults related to electric heating boilers are greatly reduced. According to the actual use, after the use of programmable controller to control the electric heating boiler, the operation of the electric heating boiler is more stable, and all kinds of fault problems are reduced by nearly 70%. Using programmable controller to control the electric heater can greatly improve the automation control degree of the electric heating boiler, effectively enhance the control reliability and sensitivity of the electric heating boiler, and play a positive role in the control of the electric heating boiler and the protection of components.