Nonlinear dew point temperature curve in the hollysys LM series PLC in the implementation

Abstract: in this paper, related to humidity dew point temperature of the data processing as an example, introduces the dew point temperature curve method in hollysys LM series PLC. At present, the use by PLC controller, text screen and sensor transmitter system instead of the single chip microcomputer system composed by the way, has been widely used in the field of analysis and detection. Keywords: hollysys LM series PLC; Dew point temperature; Nonlinear curve 1 overview with all walks of life more and more high to the requirement of humidity measurement, humidity measurement has gradually become a new technology. Based on the related to humidity dew point temperature data processing as an example, introduces the dew point temperature curve method in hollysys LM series PLC. The country was formally established in 1986, the humidity and moisture professional committee, and the academic communication for many times, some of humidity also gradually establish metrological verification procedures. In accordance with the relevant regulations, humidity is defined as the water vapor content of gas, the commonly used unit is PPM. Traditionally, dew point - 20 ℃ is bounded, the measured gas into high humidity and low humidity, gas. Refers to the air dew point temperature in the water vapor content and pressure are not change conditions, cooling to the saturation temperature. Figuratively speaking, is the temperature at which the water vapor in the air into dew dew point temperature. The dew point temperature is a temperature, but why use it to represent the humidity? This is because, when the water vapor in the air has been saturated, the temperature and dew point temperature is the same. When the water vapor in the air is not saturated, the temperature must be above the dew point temperature. So the dew point temperature and the temperature difference can represent the water vapor saturation degree in the air. As shown in table 1 PPM and dew point temperature of discrete statistical relationship. 2 humidity detection algorithm design of PPM value by special transmitter to hollysys LM series PLC LM3310B input module has high precision. According to table 1, the relation between PLC to calculate the dew point temperature, and in the text on the display, at the same time, with the average of the multi-channel temperature dew point as a key parameter, participate in the big system of discrete control and process control. The table 1 shows that PPM and the relationship between the dew point temperature of 55 discrete points. If the instruction (PLC characteristic curve CHARCURVE) , the coordinate points can't more than 11. So using the method of curve fitting of discrete points, discrete points plotted on a graph, the curve fitting formula. Practice shows that due to the nonlinear characteristic curves, a curve is insufficient to meet the precision, so it is divided into five interval, using five formulas to express. Input the five formulas to PLC, by PLC according to the formula to calculate the dew point temperature. First of all, according to the PPM from small to large, coordinate point order a range of five cross each other: 0. In 184, 4. 6] ,( 4. 6 reached] ,( 80841] ,( 841234 6] ,( 2346603 2] 。 And then according to the planned interval fitting out five nonlinear curve, and the nonlinear curve corresponding formulas are given, as shown in table 2. Table 2 PPM and dew point temperature of the nonlinear fitting curve 3 humidity detection system based on PLC design dew point analysis system controlled by PLC as the core of cabinets, actuators, sound and light alarm, and primary and secondary peripheral components, system device is shown in figure 1. Equipped with PLC and alarm relay in the control cabinet. PLC use hollysys LM series PLC. This system chooses the CPU module is the smallest one LM3104 LM series, ontology integration on digital quantity input at 8 o 'clock and 6 o 'clock relay output. System USES LM3310B extends the 4 channel and high precision analog input. Display unit in the system by hollysys HD2400L text display, through a serial port to ModbusRTU RS232 serial interface communication agreement with PLC, through the text display can to monitor system operation conditions, and the parameters are set. HD2400L man-machine interface is a small, mainly with all kinds of PLC and intelligent controller with communication port to cooperate to use, in the form of text or lamps monitoring and modifying the PLC internal registers or relay value and status, to ensure that operators can freely control the machine equipment. System planning out cover, menu window, manipulation of the interface, parameter setting, curve display, about us, system help and the parameters of the background correction etc. Eight Windows. Complete the touch screen menu window the switching function of the picture. Parameter Settings window to complete the process parameters Settings for detecting instrument. Alarm list window can display real-time alarm information. Figure 1 dew point analysis of the system hardware structure diagram 4 application characteristics based on the analysis of hollysys LM series PLC gas pretreatment system has the following characteristics: ( 1) The stability and reliability, accuracy and reliability is the key to the system. Hollysys LM series PLC configuration of high-performance industrial processors, has a super fast processing speed and large capacity of memory. Gas analysis applications is generally bad working conditions on site, according to the field situation, can use the hot and humid, salt fog, prevent mould of three modules, guarantee system in the damp and hot, damp, high temperature as well as a variety of chemical erosion under the bad environment, still has a high ( 2) Powerful features and extensibility by hollysys LM series PLC with small size, high integration degree, fast computing speed, logic control characteristics such as large capacity, so the whole program in addition to the state of alarm, analogue processing function, and complex pipe automatic switch, parameter setting, prevent errors manually, and other functions. In the aspect of hardware, but also can be extended to seven modules, easy system expansion. In the aspect of software, through the mature programming method, can according to according to customer's requirements to the greatest extent to modify the control strategy and display interface.
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