Automatic ignition and anoxic protection design of

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Automatic ignition and oxygen deficiency protection design of gas heaters

Yao Shaojun 1, Yao Shaoning 2, Zhou Hanyi 2 (1. Tsinghua large and small spring fatigue experimental machine equipment parameter mathematics, Beijing 100084;

2. School of materials science and engineering, Hefei University of technology, Hefei, Anhui 230009) 1 Introduction

gas heaters are winter heating equipment fueled by natural gas, liquefied petroleum gas, etc., which are generally used in areas with relatively abundant gas. Most of the heaters produced by Chinese manufacturers are exported to European and American countries, but with the development of China's "west to East Gas Transmission" project and the development and utilization of energy, the heaters will gradually popularize the characteristics of domestic materials: families.

the ignition devices of domestic gas heaters are mostly manual. The biggest disadvantage of this kind of heaters is the low success rate of ignition. In the case of low temperature and insufficient gas, it takes several times to light; In addition, the heater cannot display the current temperature, nor can it accurately regulate the temperature. It can only control the temperature by gear. This brings inconvenience to users' use and operation. There are also electronic automatic ignition heaters in the domestic market, but they are basically imported products from abroad with high prices. Therefore, this paper introduces a design scheme of gas heater controlled by single chip microcomputer. This heater can realize automatic cycle ignition and rapid ignition (successful in an ignition cycle); It can realize accurate temperature control; And can display the current temperature; It also has the function of hypoxia protection; Moreover, it consumes less electricity and has high cost performance. The working principle and hardware design of the gas heater

2.1 ignition device and working principle of the manual gas heater

the structural diagram of the control valve of the manual gas heater is shown in Figure 2-1. Its working principle is: press the knob, the outlet valve of the open flame is opened, and then rotate the knob, and the piezoelectric lighter starts to strike a fire. If the fire is lit, The thermocouple near the fire head generates a thermoelectric potential to form a closed loop with the solenoid valve coil. After the solenoid valve coil is energized, it absorbs the ejector rod at the outlet of the open flame (as shown in Figure 2-2). At this time, the knob can be loosened and the first ignition is over. If the fire is not lit, the thermoelectric potential from the thermocouple is not enough, and the solenoid valve coil cannot hold the ejector rod, the air outlet of the open flame will be closed, and then the second ignition operation is required. This kind of manual ignition is extremely inconvenient, especially in low temperature and insufficient air volume, it often needs many operations to succeed.

2.2 improved design of the heater

for this reason, this kind of heater will be transformed. The first is to change the control valve into a valve body controlled by a single chip microcomputer. The structural diagram is shown in Figure 2-3. The valve consists of two solenoid valves: main valve and auxiliary valve. The main valve controls the main air outlet, and the auxiliary valve controls the air outlet of the open flame. The second is the transformation of the control board. Its hardware block diagram is shown in Figure 2-4. After plugging in the power supply, press the start button on the panel to set the given temperature (if it is not set, the system will operate according to the parameters stored in E ■ 2PROM). The system will automatically energize the auxiliary valve coil, open the auxiliary valve, and the pulse igniter will automatically ignite. The ignition time will be delayed for 10s. After the fire is lit, the igniter will stop ignition, otherwise close the auxiliary valve and delay for 1min, Open the auxiliary valve again and ignite according to the above method. If it is not lit after 5 cycles according to the above process, close the auxiliary valve and display the fault status on the display. After the fire is ignited, the system waits for the output signal of the normally open flame thermocouple to reach the set value. If it reaches the set value, the main valve opens and the system enters the normal working state. When the thermocouple signal is in the anoxic state, the system will automatically close the computer screen display of the main valve or the friction auxiliary wear spots and the auxiliary valve, and display the anoxic state mark on the display. The whole ignition process is automatically controlled by single chip microcomputer, which is simple and time-saving.

2.3 hypoxia protection design

as this product is a gas heater, it needs oxygen and is used in the room. Working for too long without ventilation will cause indoor hypoxia, cause human discomfort, even suffocation, and endanger personal safety, so it is necessary to have an hypoxia protection device. When the system detects that the oxygen content in the indoor air is low, it will automatically close the control valve and give an alarm to show the sign of hypoxia, reminding the user to ventilate. The working principle of the protection device is: when the fuel gas supply and oxygen supply are certain, the flame combustion temperature is also certain. As the oxygen content in the air decreases, the flame temperature also decreases. If the temperature of the normally open flame measured by the thermocouple is not enough, it can be determined that the oxygen content in the air is not enough, and it is necessary to alarm and close the control valve. The anoxic protection function of this scheme is realized in this way: the wide temperature single chip microcomputer AT89C2051 is adopted, which is equipped with an analog comparator, P1 0 and P1 1 are the input pins of the comparator. According to the American Standard, the thermoelectric potential of the thermocouple in the anoxic state is 18.5mv. Connect the potential signal of 18.5mv to P1.1 pin, in which the voltage signal at the reference end is required to be stable, so connect a voltage stabilizing device at the VCC (as shown in Figure 2-5). The flame temperature signal measured by the thermocouple is amplified and then connected to the P1 0 pin of 104 and intelligent building, and then the two electrical signals of its internal analog comparator are used. If the P1 0 pin signal is lower than the P1 1 pin signal, it indicates that there is a lack of oxygen in the room. At this time, the control valve is closed and the alarm is displayed. 2.4 hardware composition

the hardware block diagram of the gas heater is shown in Figure 2-4. The whole system is mainly composed of AT89C2051 single chip microcomputer, digital temperature sensor DS18B20, control valve, igniter and display.

the single chip microcomputer adopts the high-efficiency single chip microcomputer AT89C2051 introduced by ATMEL company of the United States. It has its own analog comparator, which can realize the function of hypoxia protection. Its instructions are fully compatible with MCS 51 series single chip computers of Intel company, and it has 2K bytes

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