Light meter
AssigneeLambda Instruments, Inc.
InventorsW. Walter Biggs, Jerome E. Johnston, Lyle R. Middendorf
Life of this patent
Estimating the term…
Abstract
To permit a portable light meter to operate without zero adjustment and without excessive battery drain, a chopper-stabilized amplifier amplifies the DC signal from the light sensor of the light meter. The chopper in the chopper-stabilized amplifier is an FET circuit having a high impedance compensating circuit to avoid battery drain while compensating for interelectrode capacitance. The power supply obtains the ground level potential from the output of an operational amplifier with negative and positive potentials being generated from that reference potential so as to not require a center tap on the battery pack.
Claims15
A light meter comprising:
- sensor means for developing an electrical signal representing radiant energy impinging upon said sensor means;
- amplifier means electrically connected to said sensor means for amplifying said electrical signal without a DC potential error;
- said amplifier means including conductor means for receiving a ground level signal, a positive potential and a negative potential for operation of said amplifier means;
- a constant potential DC power supply for said amplifier means including a three terminal constant current source, whereby said light meter is portable;
- each of said terminals of said constant current source applying a different one of said positive potential, ground level potential and negative potential to said amplifier means;
- said power supply including means for developing a ground level signal;
- said means for developing including an amplifier;
- said amplifier means being adapted to be electrically connected to a battery pack;
- and
- said ground level signal being developed at the output of said amplifier, whereby a center tap for the battery pack is not needed in said power supply.
A light meter comprising:
- sensor means for developing an electrical signal representing radiant energy impinging upon said energy means;
- amplifier means electrically connected to said sensor means for amplifying said electrical signal without a DC potential error;
- said amplifier means including conductor means for receiving a ground potential, a positive potential and a negative potential, whereby electrical energy is applied to said amplifier means to permit operation;
- a constant potential DC power supply for said amplifier means including a three terminal constant current source, whereby said light meter is portable;
- each of said three terminals being electrically connected to a different one of said conductor means;
- and
- said amplifier means including a chopper-stabilized amplifier.
A light meter according to claim 15 in which said chopper-stabilized amplifier includes a bandpass filter, whereby oscillation at lower power levels is avoided.
Dependencies are inferred from the claim text.