Abstract: A fluid flow detection monitor (80), particularly useful in monitoring pressure differentials between a controlled environment and its surroundings, includes a heat source (1) situated between an upstream and downstream thermal sensor (2,3) within a channel (5). The electrical resistance of the downstream sensor varies as the downstream sensor is heated from fluid carried past the heat source. Circuitry is used to detect the electrical resistance differential between the thermal sensors, thereby detecting the presence of fluid flow.

Abstract: A subharmonic noise reduction circuit having an input terminal and an output terminal. The circuit has a first differential amplifier with a first non-inverting input, a first inverting input and a first output. The overall circuit input terminal is connected to the first non-inverting input. A low-pass filter is connected between the first output and the first inverting input. A second differential amplifier has a second non-inverting input, a second inverting input and a second output. The second output is connected to the overall circuit output terminal. A first resistor is connected between the second output and the second inverting input. A second resistor is connected between the first non-inverting input and the second non-inverting input. The circuit operates at unity gain of the DC voltage component and thus the DC output voltage follows the DC input voltage.