ELECTRONICALLY CONTROLLED DIRECT INJECTION FOAM DELIVERY AND CONDUCTIVITY BASED FLOW REGULATION OF FOAM INTO A WATER STREAM

摘要

Fire fighting equipment uses an electronically controlled direct injection foam delivery system (10). A water pump (14) pumps water through a pipe (2.4). A foam pump (36) pumps foam into a mixing chamber (46) within the pipe to produce a water-foam mixture. A microprocessor-based control circuit (20) controls the water pump and foam pump. A conductivity sensor (50) is coupled in-line with the pipe for monitoring conductivity of the mixture and providing a feedback signal to the control circuit to regulate the foam pump. The conductivity sensor uses stainless steel plates (60,62) positioned in the flow stream of the pipe for measuring conductivity of the mixture. An interface circuit (54) generates a voltage having dual polarity and a fifty percent duty cycle for the conductivity sensor. A second conductivity sensor (30) monitors conductivity of the water and provides a feedback signal to the control circuit.