US3690773A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Dual photoconductive cell photometer
Assignee: UNILEX Inc
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Filing: 1970-11-19
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Granted: 1972-09-12
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Expires: 1990-11-19
Abstract
Abstract A photometer for measuring the color of aqueous solutions such as polluted water with great sensitivity is provided. The photometer is portable, operates on a low power source, and retains sensitivity despite shock or drift of either the energy source or the light source. The photometer utilizes photoconductive cells in a manner to eliminate the ''''light history'''' effect. A sample filter cell is placed between the lamp source and a regulating filter, which in turn is in front of a first cell, the second filter being designed to reduce the total light reaching the first cell. A second photoconductive cell is positioned to view light directly from the source and at the same time light reflected off of the sample filter. The cells are on opposite legs of a bridge circuit with each leg of the circuit being shunted around the cells to provide for drift control and balance. The bridge circuit is operated at low voltage across each photocell. The difference between the spectral response of the cells is balanced by the impedence of each leg circuit. The color intensity difference between sample filters is read directly on a microammeter across the bridge, the ammeter being chosen to provide as little impedence across the bridge as possible.
Inventors
- 👤 Frank Malley
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-06 23:03
CPC Classifications
G; G01; G01J; G01J3/00; G01J3/46; G01J1/00; G01J1/10; G01J1/16; G01J1/1626; G01N; G01N21/00; G01N21/17; G01N21/25; G01N21/255; G01J3/50; G01J3/51
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
148 words
An electrical photometer comprising a radiation source, a first photoconductive cell in position to respond to changes in the level of intensity from said radiation source, a filter sample in the radiation path between said source and said first cell, a chromatic filter control means in the radiation path between said filter and said first cell to reduce the radiation intensity level reaching said cell to a sufficiently low level so as to essentially eliminate the hysteresis effect common to photoconductive cells, a second photoconductive cell with means for providing radiation to said second cell both directly from the radiation source and reflectedly from the radiation source off of the filter sample, and a series adding circuit means for measuring a difference in the conductive response between the two cells, so that the difference between the responses is directly proportional to the color intensity of the sample cell.
Claim 2
Dependent Claim
148 words
An electrical photometer comprising a radiation source, a first photoconductive cell in position to respond to changes in the level of intensity from said radiation source, a filter sample in the radiation path between said source and said first cell, a chromatic filter control means in the radiation path between said filter and said first cell to reduce the radiation intensity level reaching said cell to a sufficiently low level so as to essentially eliminate the hysteresis effect common to photoconductive cells, a second photoconductive cell with means for providing radiation to said second cell both directly from the radiation source and reflectedly from the radiation source off of the filter sample, and a series adding circuit means for measuring a difference in the conductive response between the two cells, so that the difference between the responses is directly proportional to the color intensity of the sample cell.
Claim 3
Dependent Claim
40 words
The photometer of claim 1 wherein the filter sample is the colored liquid product of a chemical reaction with pollutants in water wherein the color intensity of the product is proportional to the concentration of the pollutant to be measured.
Claim 4
Dependent Claim
23 words
The photometer of claim 1 wherein the control means is chosen to adjust the radiation reaching the first cell to be essentially monochromatic.
Claim 5
Dependent Claim
42 words
The photometer of claim 3 wherein the control means is at least one colored filter, the color of the filter being chosen to absorb essentially all of the source radiation at the wave lengths of the peak transmission of the sample filter.
Claim 6
Dependent Claim
25 words
The photometer of claim 1 wherein the control means is chosen to lower the radiation level reaching the first cell to intensity below 2 foot-candles.
Claim 7
Dependent Claim
25 words
The photometer of claim 1 wherein the control means is chosen to lower the radiation level reaching the first cell to intensity below one foot-candle.
Claim 8
Dependent Claim
57 words
The photometer of claim 1 wherein the means for providing radiation to the second cell comprises a reflector around the radiation source, with a penetration in the reflector into which the second cell is placed in a position to receive a combination of radiation from the source and reflected radiation from the surface of the sample filter.
Claim 9
Dependent Claim
53 words
The photometer of claim 1 wherein the circuit means is a direct current electrical bridge circuit with each of the cells located on opposite legs of the bridge circuit wherein unbalancing of the bridge produces a current flow change within the bridge that is proportional to the color intensity of the sample filter.
Claim 10
Dependent Claim
43 words
The photometer of claim 8 wherein the unbalancing of the bridge circuit is measured by a microammeter in the bridge, said microammeter having as little internal impedence as possible as long as it does not shunt any of the legs of the circuit.
Claim 11
Dependent Claim
21 words
The photometer of claim 8 wherein the microammeter has an internal impedence in the range of about 700 to 1,800 ohms.
Claim 12
Dependent Claim
43 words
The photometer of claim 8 wherein the bridge circuit has at least one cell shunted with a variable resistor to insure that the resistance of the whole leg of circuit is in balance with the other leg to act as an anti-drift control.
Claim 13
Dependent Claim
46 words
The photometer of claim 11 wherein in the bridge circuit the first cell is shunted with a variable resistor as anti-drift control and the second cell is shunted with a resistor just higher in impedence than that of the second cell when the source is on.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-09-12 | 1976-03-13 | 1976-09-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-09-12 | 1980-03-13 | 1980-09-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-09-12 | 1984-03-13 | 1984-09-12 | $7700.00 | Window Closed / Lapsed |