temperature alarm

temperature alarm This design allows a simultaneous check of a maxi- mum of four temperatures. The individual detectors are connected to the main control unit by means of a pair of wires. When one of the detectors registers an abnormally high or low temperature, an alarm sounds. The positioning of resistor R10 determines whether the alarm is activated when the registered temperature rises above the preset temperature setting or whether it sounds when it falls below the required temperature. When R10 is incorporated between the positive supply line and the output of IC3, the alarm will be triggered when the measured temperature ex- this situation the ceeds that of the setting output of IC3 falls and the detector starts to draw a current of around 20 mA. This means that the voltage across R1 becomes greater than 0.6 V causing transistor Ti to conduct and the alarm to sound. This occurs because as the temperature rises the resistance of the NTC resistor (R9) de- creases taking the in...