Aspirated smoke fire detector, fire protection system, airflow detection circuit and method

An aspirated smoke fire detector, comprising an airflow detection circuit, the airflow detection circuit comprising:

• a first thermistor, wherein one terminal of the first thermistor is coupled to a first resistor and a first switch, and the other terminal of the first thermistor is coupled to a first input terminal of a first operational amplifier;
• a second thermistor, wherein one terminal of the second thermistor is coupled to the first resistor and the first switch, and the other terminal of the second thermistor is coupled to a second input terminal of the first operational amplifier;
• a voltage source, coupled to the first resistor and the first switch and configured to provide a supply voltage for the first thermistor and the second thermistor through a corresponding supply path based on ON or OFF of the first switch;
• and
• a controller, coupled to an output terminal of the first operational amplifier and configured to collect an output signal of the first operational amplifier and determine an airflow flow rate based on the output signal.

An airflow detection method, comprising:

• collecting an airflow to be detected;
• collecting, based on the airflow to be detected, an output signal of an airflow detection circuit;
• determining, based on the output signal, a duty cycle;
• and
• determining, based on the duty cycle, an airflow flow rate;
• wherein the airflow detection method is performed by an aspirated smoke fire detector, wherein the aspirated smoke fire detector comprises an airflow detection circuit, the airflow detection circuit comprising:
• a first thermistor, wherein one terminal of the first thermistor is coupled to a first resistor and a first switch, and the other terminal of the first thermistor is coupled to a first input terminal of a first operational amplifier;
• a second thermistor, wherein one terminal of the second thermistor is coupled to the first resistor and the first switch, and the other terminal of the second thermistor is coupled to a second input terminal of the first operational amplifier;
• a voltage source, coupled to the first resistor and the first switch and configured to provide a supply voltage for the first thermistor and the second thermistor through a corresponding supply path based on ON or OFF of the first switch;
• and
• a controller, coupled to an output terminal of the first operational amplifier and configured to collect an output signal of the first operational amplifier and determine an airflow flow rate based on the output signal.