Initial roasting of tobacco is an important part of the production of tobacco, a pit smoke is 5 ~ 7 days (the lower smoke, central smoke, the upper cigarette bake time) To complete a series of physicochemical changes, so that the freshbed leaves become orange and have good Leaves of tissue, elastic, gloss, oil and aroma. To achieve this goal, it is necessary to scientifically and implement the "three-stage" process requirements, and the core of the "three-stage" baking process is determined according to the specific state of tobacco leaves and control the yellowing period, the set color and the dry tendon period. Each heating section, dry and wet temperature of the insulation section (dry temperature refers to the air
Filter Fan Ventilation Filter Fan
temperature in the pit room, the wet temperature refers to the water temperature in the pit room). At present, the vast tobacco area has been widely promoted to the "three-section" baking process of booming of tobacco leaves, and most of the pit room has been installed with hot air circulation devices, while the dry and wet temperature measuring instruments are alcohol or kerosene glass tubes. The thermometer (called fire meter is called in the smoke area), the control method uses artificial opening and closing wind doors (for moisture, control wet temperatures), wind doors or blowers (controlling fire furnace fire, indirect control dry temperature). The temperature measurement is not allowed, the use of inconvenient glass tube thermometers, the passive control method plus the operator has become a bottle diameter problem that is improved in the improvement of tobacco baking quality for more than 5 days.
In recent years, many scientific workers have made a lot of work to solve the problem of solving flue-tobacco wet temperature measurements and control problems. However, due to the factors affecting the wet temperature in the pit housing in the primary roasting of the pit, the mathematical model cannot be established, and the routine control method is difficult to achieve the expected control goal. To this end, the flue-cured tobacco pit housing intelligent dry and humidity controller (hereinafter referred to as the measuring and controller), the automatic control of dry and wet temperature is basically realized, and the baking process can be randomly changed, and there is a good promotion application value.
1 design plan and technical indicators
Practice shows that during the baking of the tobacco leaves, whether there is a fresh macarriage, regardless of the yellow period, the set-color period or the dry tendon, the temperature rise rate of the heating section is optimized at 1 ° C per hour, while the temperature of the heat preservation In the time, according to the specific situation of the fresh macarriage. In the flue-barrier pit room, if the hot air circulation device is not installed, the upper and lower temperature differences in the pit can reach 10 ° C, and the upper and lower temperature differences inside the hot air circulation pit are also 4 ~ 5 ° C, and the temperature difference of the pit is random, so if you want After the comprehensive measurement results after multi-point measurement, the control is reasonable, but in practice. Practice shows: If the dry wet temperature in the pit can be controlled within ± 2 ° C, the baking quality is reliable, and the baking quality is reliable.
According to the requirements of the use, the heating section of the region, the set color area, and the dry tendon region is set to 1 ° C / h; in order to adapt to the baking of different tobacco leaves, the ideal curve of the dry temperature is provided as shown in FIG.
Figure 1 Dry temperature control curve
In order to adapt to the baking of different tobacco leaves, the temperature control gear is set by artificial buttons. In the range of 38 ~ 68 ° C, the temperature gear position is set to 5 gears. When it is initially set to 1, the temperature rise rate from the roasting temperature to 38 ° C is 1 ° C / h, and the ideal temperature at any time is determined. When the temperature rises to 38 ° C, automatically enter the insulation control state, the holding time until the next grade setting; if the second set is 3, it will increase from 38 ° C to 45 ° C to heater, lift When it is 45 ° C, it automatically enters the insulation state, and the other gear is pushed. When the power is applied in use, the actual temperature in the current pit is continuously operated by the above law.
Controlling wet temperature is an important part of ensuring baking, in order to adapt to different tobacco leaves and increase artificial initiative, the temperature gear position in the 35-43 ° C range is set to 9 gears, and the wet temperature control curve is shown in FIG. The gear setting and control law are similar to dry temperature.
Figure 2 Wet temperature control curve
The main technical indicators of the measuring controller are as follows:
Effective measurement and control range: 20 ~ 80 ° C;
Display resolution: 0.1 ° C;
Measurement accuracy: ± 0.5 ° C;
Control accuracy: ± 1 ° C;
The temperature rate of heating section was heated: 1 ° C / h.
2 system composition
The controller system consists of the host, sensor assembly, and execution components. The hardware system is shown in Figure 3.
Figure 3 System Structure Schematic
The measurement and controller precision is required to be 0.5. According to the control function, the system is used to select the AT89C51 as the CPU. AT89C51 is a low-power, high-performance film 4KB flash programmable / erase read-only memory 8-bit CMOS microcontroller, compatible with MCS-51 microcontroller product series, high-density, non-volatile Storage technology is manufactured, and the memory can be recycled / erased 1000 times. The A / D converter uses the ADC1005CMOS10 bit A / D converter. The chip resolution is 8 bits, and the total non-adjustment error is ± 1 lsb, the output level is compatible with TTL levels, and the single power supply + 5V is powered. The analog input range is from 0 to 5V.
There are 3 output channels: 1 alarm circuit, using a tumble alarm; 2 drive circuits control the forward and reverse rotation of the electric actuator. In order to improve the anti-interference ability of the system, the drive circuit uses an AC solid state relay.
The temperature gear setting uses the BCD code dial, using the low position of P1 as a digital input, and the operation is convenient.
The temperature display is displayed in LED. In order no longer expand the parallel interface, the three-bit static display LED interface circuit is extended by the shift register function of the serial port. P1.7 is used as an output control when P1.7 = 1 allows the serial port to output data to the shift register, otherwise, the display content is unchanged.
The sensor assembly consists of a sensor, a wet temperature kettle and a wire connector. According to the measurement and control accuracy requirements, the system selects the Cu50 thermal resistance as a temperature sensor. Cu50 measurement range -50 ~ + 150 ° C, good linearity, high sensitivity, moderate price, can meet the technical requirements of the system. The temperature control first depends on the temperature measurement accuracy, so in order to ensure accuracy, the hardware uses three measures: First, the connection of the sensor in the measurement adopts a new three-wire method, compensates for the error caused by the wire; second, The OP07 is selected as an operational amplification circuit, and third, the measurement circuit is powered by a constant current source.