US4310243A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Spectrophotometer with photomultiplier tube dark signal compensation
Assignee: Beckman Coulter Inc
•
Filing: 1979-10-19
•
Granted: 1982-01-12
•
Expires: 1999-10-19
Abstract
Abstract In a spectrophotometer including a photomultiplier tube and an operational amplifier responsive to the current from the photomultiplier tube for generating a DC voltage proportional to light intensity, a method and means for simultaneously compensating for the dark current of the photomultiplier tube and the offset of the operational amplifier so that the output voltage of the operational amplifier is zero volts under dark conditions.
Inventors
- 👤 James R. Brown
- 👤 Allen M. Diamond
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 15:03
CPC Classifications
H; H01; H01J; H01J40/00; H01J40/02; H01J40/14; G; G01; G01J; G01J1/00; G01J1/42; G01J1/44
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
197 words
In a spectrophotometer including a source of light, a detector responsive to said light for producing a signal proportional to the intensity thereof, and an operational amplifier responsive to the signal from said detector for generating an output signal proportional to intensity, said operational amplifier having inverting and non-inverting inputs and an output, the signal from said detector being applied to said inverting input of said operational amplifier, and a low pass filter coupled between said inverting input of said operational amplifier and said output thereof for filtering the signal applied to said inverting input, the improvement comprising: means for establishing a dark condition for said detector; and feedback means for adjusting the output signal of said operational amplifier to zero volts during said dark condition, said means including means responsive to said output signal of said operational amplifier during said dark condition for generating a reference voltage, means for applying said reference voltage to said non-inverting input of said operational amplifier for reducing said output signal to zero, and means for determining whether said reference voltage reduces said ouput signal to zero and for adjusting said reference voltage until said output signal is reduced to zero.
Claim 2
Dependent Claim
197 words
In a spectrophotometer including a source of light, a detector responsive to said light for producing a signal proportional to the intensity thereof, and an operational amplifier responsive to the signal from said detector for generating an output signal proportional to intensity, said operational amplifier having inverting and non-inverting inputs and an output, the signal from said detector being applied to said inverting input of said operational amplifier, and a low pass filter coupled between said inverting input of said operational amplifier and said output thereof for filtering the signal applied to said inverting input, the improvement comprising: means for establishing a dark condition for said detector; and feedback means for adjusting the output signal of said operational amplifier to zero volts during said dark condition, said means including means responsive to said output signal of said operational amplifier during said dark condition for generating a reference voltage, means for applying said reference voltage to said non-inverting input of said operational amplifier for reducing said output signal to zero, and means for determining whether said reference voltage reduces said ouput signal to zero and for adjusting said reference voltage until said output signal is reduced to zero.
Claim 3
Dependent Claim
35 words
In a spectrophotometer according to claim 1, the improvement wherein said means for establishing a dark condition comprises a shutter controllable to selectively block the light path between said source of light and said detector.
Claim 4
Dependent Claim
36 words
In a spectrophotometer according to claim 1 or 2, the improvement wherein a resistor is connected to said non-inverting input of said operational amplifier and wherein said feedback means feeds back a current through said resistor.
Claim 5
Dependent Claim
65 words
In a spectrophotometer according to claim 1 or 2, the improvement wherein said feedback means comprises: an analog-to-digital converter responsive to said output signal of said operational amplifier for converting said output signal to a digital signal; calculator means responsive to said digital signal for generating a digital feedback signal; and a digital-to-analog converter for converting said digital feedback signal to an analog reference signal.
Claim 6
Dependent Claim
183 words
In a spectrophotometer including a source of light, a detector responsive to said light for producing a signal proportional to the intensity thereof, an operational amplifier responsive to the signal from said detector for generating an output signal proportional to intensity, said operational amplifier having inverting and non-inverting inputs and an output, the signal from said detector being applied to said inverting input of said operational amplifier, and a low pass filter coupled between said inverting input of said operational amplifier and said output thereof for filtering the signal applied to said inverting input, a method for simultaneously compensating for dark current of said detector and offset of said operational amplifier so that said output signal of said operational amplifier is zero volts under dark conditions, comprising the steps of: establishing a dark condition for said detector; sensing the value of said output signal from said operational amplifier during said dark condition; feeding back to the non-inverting input of said operational amplifier a reference signal for reducing said output signal to zero; and repeating the above steps until said output signal is zero.
Claim 7
Dependent Claim
183 words
In a spectrophotometer including a source of light, a detector responsive to said light for producing a signal proportional to the intensity thereof, an operational amplifier responsive to the signal from said detector for generating an output signal proportional to intensity, said operational amplifier having inverting and non-inverting inputs and an output, the signal from said detector being applied to said inverting input of said operational amplifier, and a low pass filter coupled between said inverting input of said operational amplifier and said output thereof for filtering the signal applied to said inverting input, a method for simultaneously compensating for dark current of said detector and offset of said operational amplifier so that said output signal of said operational amplifier is zero volts under dark conditions, comprising the steps of: establishing a dark condition for said detector; sensing the value of said output signal from said operational amplifier during said dark condition; feeding back to the non-inverting input of said operational amplifier a reference signal for reducing said output signal to zero; and repeating the above steps until said output signal is zero.
Claim 8
Dependent Claim
27 words
A method according to claim 5, wherein said step of establishing a dark condition comprises blocking the light path between said source of light and said detector.
Claim 9
Dependent Claim
64 words
A method according to claim 5 or 6, wherein said step of feeding back a reference signal to said operational amplifier comprises the steps of: converting said output signal to a digital signal; calculating from said digital signal the value of a digital reference signal; and converting the value of said digital reference signal to an analog signal for application to said operational amplifier.
References Cited (Backward Citations)
US2253976A
Cited
US3684378A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1985-01-11 | 1985-07-13 | 1986-01-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1989-01-11 | 1989-07-13 | 1990-01-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1993-01-11 | 1993-07-13 | 1994-01-12 | $7700.00 | Window Closed / Lapsed |