Low temperature thermostat design

Low temperature thermostat design

According to the temperature change of the working environment, a physical deformation occurs inside the switch, which produces certain special effects, and generates a series of automatic control components, such as a temperature control switch, also called a temperature protector or a temperature controller. Referred to as the thermostat. Or through the temperature protector to pass the temperature to the temperature controller, the temperature controller issues a switch command to control the operation of the device to achieve the desired temperature and energy saving effect.

About the thermostat design as follows:

Introduction The hot melt machine needs stable high temperature to achieve normal operation. According to the difference between the set temperature and the measured temperature, the relay heating is controlled, so that the temperature is always controlled at the set temperature. The system uses the MICROCHIP company's PICl8F252 chip. For the processor, in the program, the main solution is to obtain the temperature value, the temperature is set by the keyboard, A/D conversion, timing interrupt, and the like. 1 System function 1.1 The right button of the thermostat panel is: (S1) Top left: Set increase button (S2) Upper right: Set down button (S3) Left middle: Plastic bucket selection button (S4) Right center: Spray head selection Key (S5) Bottom left: Set/confirm button (K0) Bottom right: Open key 1.2 Thermostat panel Left digital tube from top to bottom: Red: Plastic barrel current temperature (-99400) Green: Plastic barrel Constant temperature (0300) red: current temperature of the nozzle (-99400) green: nozzle setting temperature (0300) 1.3 LED panel on the right side of the digital tube of the thermostat panel is the working indication of the SSR (ie heating tube) of the corresponding circuit. The LED lights up when the SSR is turned on (ie, the heating tube is energized). 1.4 Two LED lights on the lower right side of the thermostat panel: the power indicator on the left and the fault indicator on the right. 1.5 The temperature controller has the following alarm functions: temperature abnormal alarm E00, heating process abnormal alarm E01, heating process abnormal alarm E02, temperature maintenance process abnormal alarm E03, alarm elimination. 1.6SSR connection sequence: If all the circuit setting temperatures are greater than the ambient temperature during startup, the SSRs of the glue barrel and nozzle circuits are sequentially turned on, with an interval of about 0.5 seconds. Follow the same rules when shutting down or abnormally disconnecting the SSR. 2 system principle analysis The basic workflow of the system is: the temperature is converted into a weak voltage, input to the pin of HCl38, and then the digital temperature is converted by the digital-to-analog conversion, in order to prevent deviation, in the process of obtaining the measured temperature, In the form of digital filtering, after reading 32 times, the average value is obtained, so that the measured temperature value is obtained. The user can set the temperature through the keyboard to control the operation of the relay. After the measured temperature is set and the temperature is set, the system automatically compares the difference between them to determine whether it is full or semi-heated. At the same time, the system also detects four alerts and alerts you. Therefore, the functions that the system needs to implement are: digital filtering, voltage-to-temperature conversion, scanning keyboard to read user input, reading user input set temperature, determining heating or not, detecting alarm, and outputting relay control related variables to HC595, the output of the digital tube. The system adopts MICROCHIP's PICl8F252 chip as the processor, and is connected with a HCl38, four HCl64, HC595, etc., HCl38 is a kind of function, and HCl64 cooperates with HCl38 to realize the display function of the digital tube. Four rows of digital tubes. The HC595 is connected to a relay and is responsible for controlling the relevant parameters. The PICl8F252 chip has 28 pins, each with RA, RB, and RC, each with eight pins, and also supports a ten-bit A/D conversion mode. In the implementation of the interrupt, the chip uses two special registers TMR0 and TMRl, the two chips have corresponding high and low bits respectively. For each instruction executed, TMRlL is incremented by 0x01, and for each 0x06 of TMRlL, TMROL is incremented by 0x01. When the corresponding lower bit overflows, the corresponding high bit will be incremented by 0x01. In this way, when the high bit overflows, it will jump into the interrupt in the program to execute the relevant instruction. The C port realizes the output of HCl38 and HCl64 respectively, the B port realizes the output of HC595, and the 0 pin to the 4 pin of the A port are responsible for receiving the processed weak voltage, that is, the analog input voltage. In the voltage-to-temperature conversion, the input voltage is between 0.5V and 3.5V, and there is a linear relationship between the input voltage and the read temperature. After the voltage input comes in, the corresponding ten bits indicate this. The voltage, at 1024, corresponds to 5.0V. In the process of numerical conversion, the input data is shifted to the right by one bit (ie, divided by 2). After the average value is obtained, it is adjusted. If the value is greater than 100, the value is greater than 100. , directly reduce 100, you get the measured temperature, otherwise, the value of the temperature is a negative value, you must set the negative flag to 0, and that value is the absolute value of the measured temperature, HCl64 with HCl38 to achieve the display function of the digital tube .