Abstract: A switchless circuit malfunction sensor utilizes only two leads, connecting open circuit sensors in parallel across the leads and closed circuit sensors in series in line with the leads. A continuity module at one end of the sensor line permits the wiring status of the monitored circuit to be constantly monitored for breaks or shorts. The continuity module can be coupled to an alarm system to activate an audio or visual signal if a circuit malfunction is sensed.

Abstract: An air flow sensor has a hollow tubular housing partially filled with potting compound and having a printed circuit board mounted in the compound inside the tube. The board is mounted such that two power resistors and a first heat sensing switch mounted on the board are embedded in the potting compound, and a second heat sensing switch mounted on the board above the compound is in contact with the ambient atmosphere. The power resistors are connected in parallel to a power source driving a fan, and the first switch has an actuation temperature selected to activate the switch when the power resistors radiate a selected amount of heat. The second switch also has an actuation temperature due to lack of air flow chosen to activate the switch when the ambient atmosphere reaches the designated temperature.