CONSTANT LIGHT INTENSITY SERVO CONTROL UNIT

• US 3,558,892 A
• Filed: 11/29/1968
• Issued: 01/26/1971
• Est. Priority Date: 11/29/1968
• Status: Expired due to Term

• Current Assignee: Robert L. Seeley
• Original Assignee: Robert L. Seeley
• Inventors: Seeley, Robert L.
• Application Number:
  US04/780,942
• Time in Patent Office: 788 Days
• US Class Current: 250/205
• CPC Class Codes: H05B 39/042 by measuring the incident light
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps

Abstract

The present disclosure relates to devices for controlling the light intensity of a lamp, automatically, under unfavorable conditions. Electronic servocontrol circuits have been used to maintain associated circuit elements within certain operational limits. The disclosed invention, while generally being of this type, presents a rugged, compact, servocontrol unit designed to regulate the output of a storage battery to ensure a particular light intensity of a lamp contained in a pressure-resistant housing. Precise light intensity regulation, to a degree far in excess of that discernible by the human eye, is necessary where a lamp provides a source of illumination for a remotely located nephelometer, an instrument for determining the concentration or particle size of suspensions by means of transmitted or reflected light. Such precise light intensity regulation is achieved by a serially connected control unit formed of a pair of parallel power transistors controlled by a first and a second feedback loop coupled to their bases. The first feedback loop compares a desired potential provided by a Zener diode to the output of the control unit and develops a first control signal that functions to change the bias on the two parallel transistors until the output of the control unit substantially equals the desired potential. A second feedback loop, having a photocell positioned to receive impinging radiation from the lamp, produces an output signal indicative of the lamp'"'"''"'"'s radiation intensity. A predetermined lamp intensity, causing the photocell to give a predetermined resultant signal, causes no current feedback to the control unit. A resultant signal caused by a deviation from the predetermined lamp intensity results in the creation and the transfer of a second signal to the control unit and consequent regulation of the lamp'"'"''"'"'s intensity. Thus, a circuit ensuring internal potential regulation, as well as regulation of a lamp'"'"''"'"'s intensity caused by deterioration of the lamp'"'"''"'"'s elements, provides more stable and precise light intensity regulation than contemporary circuits.

Claims

1. An apparatus for controlling the light intensity of a lamp isolated from external control comprising:

a storage battery similarly isolated from external control;

an adjustable impedance including first and second power transistors connected in parallel with their respective collectors electrically connected to said storage battery and their emitters electrically connected to said lamp for transferring an output signal thereto;

a first feedback means including a Zener diode having a breakdown voltage equal to a desired potential, a voltage sampler connected to said emitters bleeding off a portion of said output signal, and a voltage comparator coupled to said Zener diode and said voltage sampler for comparing said desired potential with said portion to pass a first signal representative of their deviation to the bases of said first and second transistors to adjust said impedance for ensuring the transfer of an output potential equal in magnitude to said desired potential;

a second feedback means including an internally carried photocell having a linear response over a limited range of light intensity to simultaneously generate a linear second signal representative of light intensity deviations from a desired light intensity caused by deterioration of said lamp, electrically connected to said bases; and

means for adding said first signal and said second signal to produce a composite signal electrically connecting said bases to said first and second feedback means for additively controlling said impedance to provide a lamp potential ensuring said desired light intensity.

2. An apparatus according to claim 1 further including:

a source of current deriving its power from said source of potential and interposed between said adjustable impedance and said first feedback means and said second feedback means, said source of current producing a current additive to said composite signal for driving said control unit.