Guys living in rural areas, and many urban students know: before posting to the Elevator, harvested grain, until dried, stored at currents in piles. However, long contain so harvest is impossible: because of the increased humidity may increase the temperature inside the piles, and the grain will spoil. To avoid this, it is shoveled (inner and outer layers are reversed). And the time when the grain begins to overheat, determined by its temperature and humidity.
To measure these parameters in a laboratory physical experiment Kuta Novosibirsk Akademgorodok developed a special device. It was built by a schoolboy Vladimir Petrik.
The device allows to measure temperatures up to 50° with an error of 5% and humidity 50% with a precision of 10-15%.
The moisture meter consists of a generator of high frequency oscillations (about 700 kHz), collected according to the scheme of the multivibrator transistors T3, T4, and measuring amplifier T1, T2, collected by a balanced circuit (Fig. 1). Capacitive humidity sensor S1 is formed by two coaxial aluminum cylinders at the end of the measuring rod (Fig. 2). To reduce interference and increase the sensitivity of the generator device and the amplifier are assembled on one printed circuit Board and placed in the rod, in the vicinity of the sensor. Metal cylinders coated with a waterproof varnish or nitro to seal them from moisture and direct contact with the grain.
Fig. 1. Schematic diagram of the device.
(The position of the switch B1: 1 — temperature 2 — humidity 3 — off.)
Fig. 2. The device of the measuring rod:
1 — pipe (aluminum), 2 — rod (ebonite), 3 — electrodes of the humidity sensor (aluminium), 4 — the case of the temperature sensor (aluminum, copper), 5 — thermometer, 6 — ring (ebonite), 7 — circuit Board.
Fig. 3. Internal view of the instrument.
Power stable multivibrator chain R13, D1.
Temperature meter bridge of Winston, one arm of which includes a thermistor R16. Food thermometer also stabilized through resistor R14 and diode D2.
Instrument setup is simple. The humidity meter is a capacitance of the capacitor C2 must be equal to the capacitance of the sensor in air. With the help of resistor R1 in the arrow of the instrument before each measurement set to 0.
The limit of the measurement device adjust the variable resistor R6 to a setting position on the control dimension of grain of known moisture content.
Temperature meter configured using variable resistors R17, R19. It is necessary to compare readings and a thermometer in the range 0-50°. With R17, the device is configured at zero temperature, and R19 is at a maximum.
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