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Anoxic protection device is an indispensable safety device for gas heater. This article introduces the application of thermocouples in the gas heater to achieve anoxic protection. The device is easy to use, has excellent performance, and reduces the manufacturing cost of the gas heater.
Gas heater is a heating device used indoors. It needs oxygen consumption during work. Working for a long time without ventilation will cause indoor hypoxia, causing discomfort to the human body, and even suffocation, which endangers personal safety. . The function of the hypoxic protection device is: when the system detects that the oxygen content of the indoor air is low, it will automatically close the control valve, and the alarm displays a hypoxia sign to remind the user to ventilate. Thermocouple is a common sensor, widely used in temperature measurement. The principle is that the two ends of two different conductors are connected into a closed loop. Due to the unequal temperature at both ends, a thermoelectric potential is generated in the loop. This phenomenon is called thermoelectricity in physics. This paper uses the thermoelectric phenomenon of thermocouple to design an anoxic protection device.
1. Working principle of hypoxia protection device
The working principle of this protection is: when the gas supply and oxygen supply are fixed, the flame combustion temperature is also fixed.When the oxygen content in the air is sufficient, the flame temperature can reach about 700 ℃; when the oxygen content in the air As it decreases, the flame temperature also decreases. According to American standards, the flame temperature in anoxic state does not exceed 450 ℃, the thermoelectric potential of K-type thermocouple at a relative temperature of 450 ℃ is 1815mV. If the temperature measured by the thermocouple is not enough, it can be considered that the oxygen content in the air is not enough, and it is necessary to call the police and close the control valve. The hypoxic protection function of this scheme is realized as follows: Adopt wide temperature single-chip AT89C2051, which has an analog comparator inside, P110 and P111 are the input pins of the comparator. Connect the potential signal of 1815mV to the P111 pin, where the voltage signal of the reference terminal needs to be stable, so connect a voltage stabilizing device at VCC. The flame temperature signal measured by the thermocouple is amplified and connected to the P110 pin, and then the internal analog comparator is used to compare the two electrical signals. If the P110 pin signal is lower than the P111 pin signal, it means that the room is hypoxic. At this time, the control valve is closed and the alarm is displayed.
Second, the hardware composition
The device is mainly composed of single chip microcomputer, thermocouple and potentiometer. The one-chip computer adopts the high-efficiency one-chip computer AT89C2051 that American ATMEL Company introduces, it has built-in analog comparator, P110 and P111 are the input pins of this comparator. Using this analog comparator can realize hypoxia protection function. The instructions of AT89C2051 are fully compatible with the MCS-51 series single-chip microcomputers of INTEL company. It has 2K bytes of flash programmable erasable read-only memory. Using this chip can greatly simplify the design of the circuit. The other functions of the device are not repeated here. The thermocouple adopts K-type thermocouple, the thermoelectric potential signal it receives is amplified and processed by the amplifier and then connected to the single chip microcomputer. The thermocouple also plays the role of collecting the constant open flame temperature signal in the heater. The potential signal of the potentiometer is 1815mV, and its reference terminal is connected to a voltage stabilizing source 358B-25.
3. Conclusion
The oxygen-deficient protection device operates normally in gas heaters and has been tested for two months of continuous operation without failure. Because the sensor uses a thermocouple, it is cheaper than other sensors, and its performance is stable. The device has a high cost performance.
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