Proportional dual beam photometer: How to achieve high-precision light absorption measurement with dual optical path design?

The core high precision secret of proportional double beam photometer lies in its mechanism of simultaneous measurement and real-time comparison, which effectively eliminates most error sources, thus achieving more stability and accuracy.

The essence of its design is to split the light emitted by the light source into two beams that alternate in time through a collimator (rotating mirror): the sample beam (SBeam) and the reference beam (RBeam). The sample beam passes through the sample solution to be tested, while the reference beam passes through a reference solution (usually a pure solvent) that serves as a reference. Subsequently, two beams of light are alternately directed onto the same detector.

The core principle of achieving high-precision measurement is as follows:

Real time compensation to eliminate fluctuations: Light source intensity drift, power supply voltage fluctuations, and detector sensitivity changes are common sources of error. In dual path design, these fluctuations will simultaneously and proportionally affect both the sample beam and the reference beam. The system quickly calculates the ratio of two signals (I-sample/I-reference) to mathematically cancel out these common fluctuations. Even if the intensity of the light source suddenly decreases, the ratio of the two remains unchanged, ensuring the stability of the measurement.

Reduce baseline drift and improve signal-to-noise ratio: Traditional single beam instruments require measuring the reference and sample sequentially, and environmental changes during this period can introduce errors. The dual beam design measures almost simultaneously, reducing the drift caused by time differences and achieving a flat baseline and high signal-to-noise ratio.

Directly reflecting the true absorbance: According to Lambert Beer's law, absorbance A=log10 (I reference/I sample). The instrument directly measures and calculates this ratio, which directly and accurately reflects the degree of light absorption of the sample, regardless of the absolute intensity of the light source.

In summary, the proportional dual beam design suppresses the majority of system errors as "common mode noise" through its working mode of simultaneous measurement, real-time comparison, and ratio calculation, thereby achieving high sensitivity, accuracy, and reliability in measuring changes in light absorption.