Flow detection apparatus

Abstract

The disclosed flow-detecting apparatus involves gating of phase-related excitation and sensed signals from electrodes close to a flow-activated tracker in a liquid passage. A high gain comparator provides peak-limited signals to the phase-comparison gate. In one form, a pair of excitation electrodes are symmetrical in relation to a single sensing electrode. That electrode supplies a sensed signal to one comparator input, the other comparator input having fixed bias. In another form, a pair of sensing electrodes are disposed in an excitation pattern between a localized excitation electrode and a metal pipe that forms the passage and acts as a second excitation electrode. The sensed signals reach respective input terminals of a high-gain comparator and it responds to the difference between the inputs. Other configurations of the electrodes and their excitation are disclosed, including one that promotes rejection of common-mode spurious signals. A comparator that receives flow-representing signals is stabilized against electrical unbalance by a negative feedback loop having a long time constant. In flow-detection apparatus having a multiple-rotor flow-sensing probe, separate flow-detection circuits are used for the respective rotors. The outputs of the flow-representing circuits are combined. Use of different excitation frequencies for those flow-detection circuits adds assurance of non-interfering operation of the flow-detection circuits.