ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Agronomist's tool. Encyclopedia of radio electronics and electrical engineering Encyclopedia of radio electronics and electrical engineering / Home, household, hobby The agronomist's device allows measuring temperature, absolute soil moisture and illumination. The main parameters
The temperature sensor is the thermistor R4, included in one of the arms of the bridge formed by resistors R1-R5. The bridge is balanced at a temperature of 0°C with a variable resistor R1. As the temperature changes, the balance is disturbed. An unbalance current, proportional to the temperature of the measured object, flows through the measuring device P1. Illumination is determined by a photocell V7. When illuminated, a current appears, measured by the same device P1. Humidity sensor - capacitive, differential. Its halves CX1 and CX2 are included respectively in the circuits L5, C14, C15 and L4, C9, C10. The circuits through the coils L2 and L3 are connected to the generator circuit, assembled on the MP42 transistor. Voltages in position Meas. wet switches S1 and S2, removed from the circuits L4, C9, C10, CX1 and L5, C14, C15, CX2, are rectified, respectively, by rectifiers on diodes V3, V5 and V4, V6, assembled according to the voltage doubling circuit. The total output voltage from capacitors C5 and C7 through resistors R12 and R13 is supplied to device P1. The first circuit is tuned to a frequency above the generator frequency (9,125 MHz), the second circuit is lower. As soil moisture increases, the sensor capacitance increases. In this case, the resonant frequency of the office L4, C9, C10, CX1 approaches the frequency of the generator, and the frequency of the circuit L5, C14, C15, CX2 moves away from it. Consequently, the RF voltage on the first circuit rises, and on the second circuit it falls. Temperature drift is compensated by capacitors C9 and C14 (with negative TKE) placed in the sensor. In the Zero and Sense positions of switch S2, the deviation of the instrument arrow to the initial and final marks of the scale is controlled before measuring the humidity. It is necessary to install gray or blue ceramic capacitors in the oscillatory circuits of the device. Capacitors C9 and C14 type KT 1a-M1300, thermistor R4 - MMT-1 or KMT-1, photocell V7 - F102 in a plastic case, diodes V3 ... V6 - any high-frequency, quartz B1 -RPK-7 with a resonant frequency of 9,125 MHz , device P1-M24 at 100 μA. All coils are wound on fluoroplastic frames with a diameter of 9 mm, the cores are SCR-1. Coils L1 ... L3 have 17,8 and 8 turns of PEL wire 0,55 mm, respectively, winding - turn to turn. Coils L2 and L3 are wound over coil L1. Between L1 and L2, L3 an open layer of copper foil is laid. Coils L4 and Z5 contain, respectively, 16 and 20 turns of the same winding wire - in bulk. Winding length - 5 mm, distance between coils - 20 mm. The humidity sensor is a stainless steel cylinder, in which two electrodes are installed on an insulating base (fluoroplast). Capacitances CX1 and CX2 are formed between the inner walls of the cylinder and the electrodes. The soil sample under study serves as a dielectric. To set up the meter, you need an avometer and a VK-7B tube voltmeter, an exemplary thermometer and a light meter, and equipment for determining soil moisture by weight. Thermistor R4 is placed in melting ice. The variable resistor R1 sets the arrow of the device P1 to the zero mark of the scale. Then the thermistor is lowered into water with a temperature of 50 ¦С and the variable resistor R11 is used to achieve the deviation of the instrument arrow to the end mark of the scale. These operations are repeated several times, after which the temperature scale is calibrated. Then the switch S1 is moved to the position Change. illumination and using an exemplary luxmeter (for example, H-16) calibrate the scale of the device. After that, the operation of the quartz oscillator is checked. The circuit L1C2 is adjusted so that the RF voltage at the collector of the transistor V2 is maximum. Switch S2 is set to zero. By rotating the cores of the coils L4 and L5, they achieve that the arrow of the device P1 is set to zero. Then, filling the sensor with soil with a moisture content of 5% and moving the switch S1 to the position Change. wet, trimmer capacitors C10 and C15 again set the arrow to zero on the scale. After that, the sensor is filled with soil with maximum moisture content. By rotating the slider of the resistor R12 and selecting the resistor R13 *, the device arrow is deflected to the end mark of the scale. Next, build a calibration graph of the device for humidity. Soil moisture is determined by the weight method. Finally, by setting switch S3 to Sense. capacitor C3 is selected and the arrow is deflected to the end mark of the scale. See other articles Section Home, household, hobby. Read and write useful comments on this article. Latest news of science and technology, new electronics: Machine for thinning flowers in gardens
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