The meter is designed to measure the temperature of the air, as if to protect sensor, and any other medium in the range -50..+50°C. I Have a meter standing on the windowsill, and measures the temperature of outdoor air. It is very convenient. In the morning when going to work, you can quickly figure out what "Okara clothes to choose from.
The circuit of the meter is a DC bridge, one shoulder which included thermistor, and an indicator is the head of the microammeter (0...50 MCA). Each division on the scale corresponds to 1°C. After equilibration of the bridge the voltage in the measuring diagonal is zero. The imbalance of the bridge causes the appearance of a voltage of positive or negative polarity depending from the direction of imbalance.
If you change the polarity of the supply voltage when the imbalance, the polarity of the voltage in the measuring diagonal of the bridge will be same when measuring positive and negative temperatures, and can to use the normal head (with the zero division on the left and not in the middle of the scale). The change of polarity is performed by the SA1 toggle-switch that has two positions: "+" and " - " that can be called "Winter" and "Summer". Measurements are made at 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. The SA1 toggle-switch - MT-3 button SB - 1 km-1. The measuring head RA1 - MA (ln=50 µa Rp=22l3 Ohms). It can be replaced by M24 or M906 with zero in the middle of the scale, then the SA1 toggle-switch is not needed. To power the device is used one element of type "D". This element 2...3 years. You can take the elements type *AA" or rechargeable batteries of the same size.
Details of the meter are placed on the Board of one-sided glass fiberglass dimensions 125x110 mm, made by cutting tracks in foil. Board mounted to the terminals of the head, its lower part serves as a support meter. In the top of the Board install the battery and one of side of the toggle switch and button.
Adjustment. Resistors R4. R7 set to the middle position. Thermistor connect wire MGTF desired length (0,5.. .1,5 m) and placed in a glass going ice after 5..10 minutes press the button SB1 Measurement resistor R7 and set to "0°. Then the thermistor is lowered in half-liter glass jar, filled with water with a temperature of +60.+70°C. the Temperature is measured mercury laboratory thermometer. After 5... 10 min. when water temperature drops to +40°C or +50°C. the resistor R4 sets the value on the scale of the instrument. The thermistor that measures the ambient temperature, it is necessary to place such a way as to prevent penetration of sunlight.
Literature
Author: Y. Plotnikov (Novosibirsk)