Over-temperature alarm and cooling circuit

This is the over-temperature alarm and a cooling by the CD4011 four NAND gate integrated circuits, and for monitoring the temperature of the oven used. When the thermostat circuit failure or power outage, the inside temperature is above or below the allowed
Over-temperature alarm and cooling circuit - schematic

range, it can sound an alarm to remind people to pay attention to take corresponding measures. The circuit has a resolving power of 0.1. Diodes VD1 and VD2 are placed in an incubator, when the inside temperature is lower than the lower limit, a figure greater than the potential of point A gate input threshold voltage U, A gate output is low, so that the door B output high level, then the door multivibrator C, consisting of start-up door D, the piezoelectric sheet sound the alarm; when the inside temperature is higher than the upper limit, b point potential is less than the gate threshold voltage B U, may be the door B output high, the piezoelectric sheet YD alarm. Only when the inside temperature is, the lower limit value between, YD will not audible. RP1 and RP2, respectively adjustment value may change the lower and upper limits respectively. AC and DC power supply circuit for the power supply, E is the standby power when AC power outage, VD3 conduction, backup power supply circuit, as the circuit consumes little, stacked battery backup power is available to reduce the volume.And sensors VD1, VD2 connected the wire is too long, it is best to use shielded cable, to enhance anti-jamming capability.Finally, chick incubation temperature monitoring to illustrate the adjustment method: First, the incubator temperature adjustment stable at 36.5, and the slide arm RP2 moved to the lowermost end, then the lower limit adjustment potentiometer RP1 adjusted so YD does not ring loud and critical place; then turn the incubator temperature regulator stable at 39.5, the upper limit was adjusted to make the adjustment potentiometer RP2 YD does not ring loud and critical place. Thus, when the incubator temperature below 36.5 or higher than 39.5, an alarm will sound, the oscillator can officially use.

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