Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Patent
1993-07-20
1995-04-11
Sikes, William L.
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
250551, 327 35, H01J 4014, G02B 2700, G01R 2306
Patent
active
054060710
ABSTRACT:
A process variable such as the load current supplied through an electrical contactor is encoded as a 4 to 20 mA current signal via an optically coupled pulse width modulated output circuit. A microprocessor produces the pulse width modulated signal at a duty cycle varying with the load current. The LED of an opto-coupler transfers the signal to a phototransistor, and a voltage regulator and switching circuit drive the phototransistor so as to minimize switching times. The voltage regulator maintains a DC voltage at the collector of the phototransistor, which is operated at a constant emitter current. The LED supplies base current to the phototransistor when the pulse width modulated signal is high. An amplifier is coupled to the emitter of the phototransistor, and the output of the amplifier is coupled back to the base of the phototransistor via a Schottky diode pair. The amplifier output varies with whether or not the base current needed to maintain constant emitter current is obtained from the LED. The amplifier output is coupled via a comparator and a low pass filter to a current driver including an amplifier and a drive transistor. The DC component of the current output varies with a duty cycle of the pulse width modulated signal, providing a 4 to 20 mA output current with variation of the load current between zero and 200% of rated load current.
REFERENCES:
patent: 4310755 (1982-01-01), Miller
patent: 4594578 (1986-06-01), Walsh
patent: 5130526 (1992-07-01), Mischel
patent: 5283441 (1994-02-01), Fabian
Instructions for Advantage Control Modules Used with Full-Voltage Two-Speed Advantage Motor Starters and Contactors Jun. 1992.
Eaton Corporation
Moran Martin J.
Nguyen Tiep H.
Sikes William L.
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