Air temperature meter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers
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The meter is designed to measure air temperature, and if the sensor is protected, then any other environment in the range of -50..+50°C. I have such a meter on the windowsill and measures the temperature of the outside air. It is very comfortable. In the morning, when you are going to work, you can quickly figure out what kind of "clothes frame" to choose.
The meter circuit is a direct current bridge, in one arm of which a thermistor is included, and the head of a microammeter (0 ... 50 μA) serves as an indicator. Each division on the scale corresponds to 1°C. After balancing the bridge, the voltage in the measuring diagonal is zero. The unbalance of the bridge causes the appearance of a voltage of positive or negative polarity - depending on the direction of the unbalance.
If you change the polarity of the supply voltage when unbalanced, the polarity of the voltage in the measuring diagonal of the bridge will be the same when measuring positive and negative temperatures, and you can use a regular head (with zero division on the left, not in the middle of the scale). The polarity change is carried out by the SA1 toggle switch, which has two positions: "+" and "-", which can be called "Winter" and "Summer". Measurements are made by pressing the button SB1.1.
Details. Thermistor R1 - 1 MMT-13B, MMT-12; resistors R2, ; R3, R5. R6 - MPT-0.5 or C2-29 with a tolerance of 5%; R4. R7 - SP5-15, SP5-14 or SP5-2. Toggle switch SA1 - MT-3, button SB1 - KM-1. Measuring head RA1 - ME06 (ln=50 μA, Rp=22l3 Ohm). It can be replaced by M24 or M906 with zero in the middle of the scale, then the SA1 toggle switch is not needed. The device is powered by one element of type "D". Such an element serves 2 ... 3 years. You can also take cells of type * AA "or batteries of the same size.
The details of the meter are located on a board made of one-sided foil fiberglass with dimensions of 125x110 mm, made by cutting tracks in the foil. The board is attached to the terminals of the head, its lower part serves as a support for the meter. A battery is installed in the upper part of the board, and a toggle switch and a button are on one of the sides.
Adjustment. Resistors R4. R7 is set to the middle position. The thermistor is connected with a MGTF wire of the required length (0,5 .. .1,5 m) and placed in a glass with melting ice, after 5..10 minutes the SB1 "Measurement" button is pressed and resistor R7 is set to "0 °. Then the thermistor is lowered into the floor liter glass jar filled with water with a temperature of +60.+70 ° C. The temperature is measured with a mercury laboratory thermometer. After 5 ... 10 minutes when the water temperature drops to +40 ° C or +50 ° C. resistor R4 set this value on the instrument scale.
Literature
- Andreev Yu.N. etc. Resistors: Handbook
- Radio, 1999, No. 6, p. 43.
- Shultz Yu. 1000 concepts for practitioners. P.130.
Author: Yu.Plotnikov, Novosibirsk
See other articles Section Power regulators, thermometers, heat stabilizers.
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