Method and apparatus for controlling the current through a magne

Details Method and apparatus for controlling the current through a magne Method and apparatus for controlling the current through a magne

1994-11-23

1995-08-15

Ganjoo, Peter

Electricity: electrical systems and devices

Control circuits for electromagnetic devices

For relays or solenoids

123490, 323285, H02H 3093, H01H 4732

Patent

active

054425158

ABSTRACT:
Apparatus and method for controlling current flow through a magnetic coil actuator of a solenoid valve. The current through the magnetic coil is measured by sensing the voltage drop across a precision resistor in series with the coil. The apparatus includes a power switch for alternately switching the coil on and off. A flyback diode is coupled in parallel with the coil for operation during coil shut-off. A first voltage sensor continuously measures the combined voltage drop across the coil and the power switch. A second sensor, coupled across the precision resistor, samples the current flowing through the coil. The samplings occur synchronously with coil turn-on, and are delayed by a predetermined time delay which is long enough to allow the current flowing through the coil to reach steady state before the current is sampled. Circuitry is provided for employing the sensed voltage signal and current samplings to produce a signal whose value is a function of the resistive component of coil impedance. Control circuitry turns the coil on at a fixed frequency. The control circuitry, however, adjusts the duration of the coil turn-on, i.e., the duty cycle, as a function of instantaneous voltage across the combined coil and power switch and also as a function of coil resistance in order to maintain current near a predetermined reference value.

REFERENCES:
patent: 4605983 (1986-08-01), Harvey
patent: 4736267 (1988-04-01), Karlmann et al.
patent: 4845420 (1989-07-01), Oshizawa et al.
patent: 5107391 (1992-04-01), Siepmann

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