Photometer including variable amplification and dark current compensation

Claim 2

Apparatus for measuring the illumination from a source of light, comprising: a photodiode for producing a current proportional to the intensity of illumination thereon; said photodiode being responsive to light having wavelengths in the range 400 to 1000 millimicrons; a differential amplifier coupled to said photodiode for receiving the current therefrom; said differential amplifier being characterized by a high input impedance; operational amplifier means coupled to said differential amplifier for amplifying said current; said operational amplifier means including first and second series connected operational amplifiers, said first operational amplifier exhibiting a constant closed loop amplification factor and said second operational amplifier exhibiting a selectively variable closed loop amplification factor; adjustable means coupled to said differential amplifier for compensating the reverse saturation current thermally generated by said photodiode to mitigate the response of said operational amplifier means to said reverse saturation current; and means coupled to said operational amplifier means and responsive to said amplified current for indicating the intensity of illumination on said photodiode.

Claim 3

The apparatus of Claim 1 wherein said adjustable means comprises a potentiometer having an adjustable contact, said potentiometer having a voltage potential induced thereacross.

Claim 4

A light meter for determining the illumination on a plane from a source of light by measuring the amount of radiant flux received at said plane, comprising : a photodiode for generating a current proportional to the amount of radiant flux incident thereon, said photodiode being characterized by a substantially uniform spectral sensitivity to radiant flux exhibiting wavelengths in the range 400 to 1, 000 millimicrons; compensating means coupled to said photodiode for minimizing thermally generated reverse saturation currents inherent in the current generated by said photodiode; indicating means responsive to a voltage applied thereto for providing an indication of said applied voltage; first operational amplifier means coupled to said compensating means, said first operational amplifier means including a feedback circuit comprised of a plurality of resistance means connected in common relationship, each of said resistance means having a distinct value of resistance, and switch means selectively connectable in series with one of said common connected resistors, to thereby provide a selectively variable closed loop amplification factor; and second operational amplifier means intercoupling said first operational amplifier means and said indicating means, said second operational amplifier means having a continuously variable amplification factor to effect calibration of said indicating means whereby said indication of said applied voltage is in units of radiant flux per unit area.

Claim 5

A light meter for determining the illumination on a plane from a source of light by measuring the amount of radiant flux received at said plane, comprising : a photodiode for generating a current proportional to the amount of radiant flux incident thereon, said photodiode being characterized by a substantially uniform spectral sensitivity to radiant flux exhibiting wavelengths in the range 400 to 1, 000 millimicrons; compensating means coupled to said photodiode for minimizing thermally generated reverse saturation currents inherent in the current generated by said photodiode; indicating means responsive to a voltage applied thereto for providing an indication of said applied voltage; first operational amplifier means coupled to said compensating means, said first operational amplifier means including a feedback circuit comprised of a plurality of resistance means connected in common relationship, each of said resistance means having a distinct value of resistance, and switch means selectively connectable in series with one of said common connected resistors, to thereby provide a selectively variable closed loop amplification factor; and second operational amplifier means intercoupling said first operational amplifier means and said indicating means, said second operational amplifier means having a continuously variable amplification factor to effect calibration of said indicating means whereby said indication of said applied voltage is in units of radiant flux per unit area.

Claim 6

A light meter in accordance with claim 3 wherein said compensating means comprises: a potentiometer having an adjustable contact, said potentiometer being supplied with a voltage potential; and a differential amplifier having a first input terminal coupled to said adjustable contact and a second input terminal coupled to said photodiode for supplying said first operational amplifier means with an input voltage.

Claim 7

A light meter for measuring radiant flux of different wavelengths received from a source of radiant energy, comprising: a photodiode exhibiting a substantially uniform spectral sensitivity characteristic to said received radiant flux for generating a current proportional to the amount of received radiant flux; a first operational amplifier arranged in closed loop configuration and coupled to said photodiode, said first operational amplifier being characterized by a fixed closed loop amplification factor; a second operational amplifier arranged in closed loop configuration and coupled to said first operational amplifier; a plurality of resistance means selectively connectable in the closed loop configuration of said second operational amplifier such that said second operational amplifier is characterized by a selectively variable closed loop amplification factor; adjustable dark current compensating means comprised of an adjustable potentiometer coupled to an input of said second operational amplifier for minimizing the response of said second operational amplifier to reverse saturation currents thermally generated by said photodiode; and indicating means coupled to an output of said second operational amplifier and responsive to a voltage produced by said second operational amplifier for providing an indication of the amount of radiant flux received by said photodiode.

Claim 8

A light meter for measuring radiant flux of different wavelengths received from a source of radiant energy, comprising: a photodiode exhibiting a substantially uniform spectral sensitivity characteristic to said received radiant flux for generating a current proportional to the amount of received radiant flux; a first operational amplifier arranged in closed loop configuration and coupled to said photodiode, said first operational amplifier being characterized by a fixed closed loop amplification factor; a second operational amplifier arranged in closed loop configuration and coupled to said first operational amplifier; a plurality of resistance means selectively connectable in the closed loop configuration of said second operational amplifier such that said second operational amplifier is characterized by a selectively variable closed loop amplification factor; adjustable dark current compensating means comprised of an adjustable potentiometer coupled to an input of said second operational amplifier for minimizing the response of said second operational amplifier to reverse saturation currents thermally generated by said photodiode; and indicating means coupled to an output of said second operational amplifier and responsive to a voltage produced by said second operational amplifier for providing an indication of the amount of radiant flux received by said photodiode.

Claim 9

A light detector circuit having an improved dark current compensating circuit comprising, in combination: a photodiode for producing a current proportional to the intensity of luminous flux incident thereon; a potentiometer having an adjustable contact, said potentiometer being supplied with a voltage potential; a differential amplifier having a first input terminal connected to said photodiode and a second input terminal connected to said adjustable contact; operational amplifier means connected to an output terminal of said differential amplifier, said operational amplifier means having a selectively variable closed loop amplification factor; and indicating means, responsive to a voltage supplied by said operational amplifier means to indicate the intensity of the luminous flux incident on said photodiode.

Claim 10

A light detector circuit having an improved dark current compensating circuit comprising, in combination: a photodiode for producing a current proportional to the intensity of luminous flux incident thereon; a potentiometer having an adjustable contact, said potentiometer being supplied with a voltage potential; a differential amplifier having a first input terminal connected to said photodiode and a second input terminal connected to said adjustable contact; operational amplifier means connected to an output terminal of said differential amplifier, said operational amplifier means having a selectively variable closed loop amplification factor; and indicating means, responsive to a voltage supplied by said operational amplifier means to indicate the intensity of the luminous flux incident on said photodiode.