Keywords: NE555, Humidity detection circuit
Be
Author: Yu Junfang
In the season of food acquisition. Many staff members of the food acquisition department. Still use the original soil measures of your hand touch or biting to determine whether the water of the food exceeds the standard, the accuracy is poor, and there is no strong persuasion to sell grain farmers. The food humidity detecting instrument introduced below will detect the humidity of the food. And the farmers who have been rejected due to the large grain humidity is good.
The food humidity detector circuit is shown in Figure 1. In the figure, R1, R2, and flat plate detecting capacitive C1 constitute a self-excited multi-harmor in the NPN type triode within the time base circuit Ne555. The cycle T = 0.7 (R1 + 2R2) C1 of the multi-resonator. Therefore, as long as R1 or R2 or C1 changes R1 or R2 or C1, the cycle (or frequency) of the oscillator can be changed, that is, the duty cycle of the NE5553 foot output rectangular wave can be adjusted. The detection mechanism of the food humidity detector is related to the capacitance of the flat plate capacitor C1 is related to its dielectric. Two area is the same. The unchanged copper plate constitutes a flat plate capacitive sensor. When the granular grain is placed between the plate capacitor sensor, the dielectric becomes a granular grain and air, and its capacitance is increased. As can be seen from the cycle formula of the above multi-resmium, the period of the oscillator will become large (i.e., the oscillation frequency is low). In addition, the humidity of the food will also cause changes in the oscillator cycle (frequency). In general, the greater the humidity of the food, the larger the oscillator cycle, the lower the oscillation frequency. The NE5553 foot output is a continuous rectangular wave, the rectangular wave, the VD2 rectification and C5 filter, the flow voltage value is formed at both ends of the voltage meter. However, before detecting food moisture, the voltage meter is actually displayed into zero by adjusting the zero zero potentiometer RP (the meter is in the middle of the dial scale). When granular grain is placed in two plates between the flat plate capacitance sensor. Due to the increase in capacitance, the oscillation frequency is lowered, the output rectangular wave duty cycle increases, the rectifier filter is high, and the voltage table pointer will be biased toward the right side of the right position, that is, the voltage meter has a read number. Obviously, the larger the grain humidity, the greater the number of voltmeter readings. Thus we can engrave the humidity indication mark in advance on the voltage gauge dial, or apply a red belt that represents the green belt and humidity of the humidity. In this way, it is convenient to measure whether the humidity of the measured food is qualified. Of course, when the different grain plays the flat plate capacitor sensor, the exhibited capacitance is not the same. Therefore, the humidity indication mark on the voltage table dial, or the broccoli indicating the humidity of the humidity and the red belt indicating the humidity failure should be 3 to 4 rows of the humidity, which is measured by measuring crops such as rice, wheat, soybeans and corn. Needs of humidity.
Be
Be
The grain humidity detector is shown in Figure 2. Its outer casing can be bonded with a thick 5 mm hard plastic or three-pinch plate, and its dimension is shown in the figure. The flat capacitive sensor C1 two plates are vertically 4.5 cm, the width of 9 cm thick 2 mm is vertically in the left side of the cartridge, and is fixed. The two-pole plate is 2 cm, and the uniform insulation wire is welded to the lower corner of the bottom of the two poles as a capacitor C1 lead (the lead line should pass through the line slot reserved in the bottom of the cassette, and the instrument is produced after the production of epoxy resin. Lay flat). The voltmeter can be used with a 85C1 square voltage meter and a range ± 2.5V. If such a voltmeter is not found, it is also modified with ± 100μA current table. The detector circuit component parameter is shown in Figure 1. The resistors R1-R3 are all used using an L / 8W metal film resistance. R4 uses a 2W metal film resistance. Both capacitors C2 ~ C4 use a pressure about 160V porcelain interversion, buttons VD1, VD2 is preferably used to use high-frequency germanial detection diode 2ap9 because it is only 0.2 V, which is conducive to improving detection sensitivity. If such a diode is not found, the emission end of the high frequency triode 3AG11, 3AG14 can also be used. In order to ensure the service life of the detector, zero zero potentiometer RP should be selected for 1W solid potentiometers, and the power switch K can be used with a plurality of small button switches. In addition to the voltage meter, the zero zero potentiometer and the power switch are mounted on the dial, the battery is installed on the inside of the box, and the remaining elements can be used as a stent using a voltage meter, a potentiometer pin as a bracket, and uses the components to use a shack method. welding. Since the detector is not often used, it is less than 20 mA. The power supply can be used with a 9V cladding battery. After the detector is produced, it can be commissioned. First adjust the adjustment of the zero potentiometer RP to stop the voltage table pointer in the "0" position in the dial, and then, the humidity of the flat-panel capacitive sensor C1 has a well-equipped food sample, and the voltage gauge should have a certain angle. (Ie, the voltage gauge has a certain reading). Then in the voltmeter zero to this voltage value, the dial arc of the voltage table pointer is plated with a green marker into green (arc width 2mm), followed by extension of the right side of this arc Online, using a red marker to coate the arc extension to a red arc of about 2 mm, arc length of 1.5 cm. And write the name of this food on the end of the arc. When the food humidity is detected, if the voltage gauge reaches the red arc region, it means that the food humidity of the detection is unqualified. If the voltage table pointer is in the green arc region, it is denoted whether the food humidity is passed. According to the same approach, the color lines of other foods on the voltage gauge indicator. The entire production debugging work ends. Due to the battery voltage, atmospheric humidity. Factors such as ambient temperature will affect the measurement results, so the voltage surface calibration must be performed before each measurement.
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