Abstract: An air conditioning control system has inputs for room temperature and air velocity voltage signals. Both signals are scaled and compared to determine which signal is larger, and the magnitude of the difference. The control circuit drives a variable speed damper motor in a direction determined by the greater of the two scaled input signals. The motor is driven at a rate proportional to the magnitude of the difference between the two signals. Means for setting the maximum and minimum open damper positions are provided within the control circuit.

Abstract: A velocity sensor enclosed within a venturi housing is disposed in a moving fluid stream. A self-heated, negative coefficient thermistor is supported in the interior of the housing to sense changes in velocity of the stream. A positive coefficient thermistor is supported on the exterior of the housing and compensated for fluctuations in the ambient air temperature. The negative coefficient thermistor is operated at a temperature substantially above ambient. An automatic starting circuit is provided for cold start-up and initially heats the negative coefficient thermistor to the elevated operating temperature.