Electronic thermometer circuit
Posted on Dec 11, 2010 4642
Electronic thermometers as shown in the circuit. RT is the thermistor, A is an integrated operational amplifier. VD1 ~ VD4 composition marked by the scribe mushroom flow channe
l, unidirectional output signal. VT1, VT2 etc. switching circuit. When the thermistor RT temperature resistance with the measured object changes to a certain degree of resistance when, A, B two points there is a difference signal output of this signal by the A amplification, after VD1 ~ VD4 rectified, added to the base of VT1 pole, VT1 conduction, VT2 off, a small light bulb mouth. Does not shine this time. Changing the electrical resistance of RP2 locator, so that A, B no difference between the two output signals, the deadline VT1, VT2 conduction, small bulbs on the light. If the mark on the temperature scale potentiometer, then the lights when reading out the measured object temperature. Rr metal shell negative temperature coefficient thermistor, model RRG3J22,20 when the resistance is lOkfl, if the glass envelope is more desirable (positive temperature coefficient thermistor may be). A use of substandard goods gain operational amplifier. VT1, VT2 leakage current is less than lOOtjLA, Lu is greater than 30. A small light bulb voltage of 2.5V or less. Ei with ZZ. 5v Instrument laminated battery, easy bureau section 4 battery.