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Electronic thermometer

   This thermometer ( Fig. ) is designed to measure temperatures in the range of 0 ... 60 C and has a linear scale. Linearity is achieved by using as a sensing element unijunction transistor type KT117. The scheme has a high efficiency, that allows you to design in a compact device. Such a device is expedient to use in the food industry, where conventional glass thermometers are not allowed.
   The circuit uses two types of OS K140UD12. Shelter serves as a stabilizer DA1 exemplary voltage source is the LED VD1. Sensing element is included in the chain BK1 NFB amplifier DA2 OS . In the scheme used ammeter with a current of 100 mA full-scale deflection.

   Connecting unijunction transistor to conclusions OS DA2 shown ).
   When establishing the unit temperature sensor placed in an environment with a minimum required temperature measurement. Resistor R8 set arrow meter PA1 initial mark on the scale. Sensing element is then placed in an environment with the maximum required temperature measuring device and install the arrow mark on the final PA1 scale. Depending on the specific parameters used unijunction transistor may require the selection of resistors R6 and R9.

Fig. Electronic thermometer. Scheme:

Electronic thermometer. Scheme: