The design includes a modulated gentle supply and digital synchronous detection for precision in chemical evaluation and environmental monitoring.
A dual-channel colorimeter is an important software in each scientific analysis and industrial functions, prized for its enhanced measurement accuracy and reliability. This instrument operates by using two separate channels—one to research the pattern and the opposite to measure a reference—permitting simultaneous comparisons that assist appropriate for variability in gentle depth and sensor responses. Such capabilities are essential for exact quantification in chemical concentrations and biomedical assays. The CN0363 is a dual-channel colorimeter reference design from Analog Units (ADI) outfitted with a modulated gentle supply transmitter, programmable achieve transimpedance amplifiers on every channel, and an ultra-low noise, 24-bit analog-to-digital converter (ADC).
The ADC’s output hyperlinks to an ordinary FPGA mezzanine card, which processes the info utilizing a synchronous detection algorithm. This design, using modulated gentle and digital synchronous detection as an alternative of a gradual supply, successfully eliminates noise at frequencies completely different from the modulation frequency, enhancing accuracy. The machine measures the ratio of sunshine absorption in pattern and reference containers at three distinct wavelengths, an important perform in varied chemical evaluation and environmental monitoring instruments that make the most of absorption spectroscopy to find out materials concentrations and traits.
A clock, set to a user-defined frequency, modulates one of many three LED colours utilizing a continuing present driver that includes the AD8615 op-amp, the ADG819 swap, and the AD5201 digital potentiometer. A beam splitter divides the emitted gentle, directing half via the pattern container and the opposite half via the reference container. The ADA4528-1, functioning as a transimpedance amplifier, converts the present from the photodiode right into a voltage sq. wave, the amplitude of which corresponds to the quantity of sunshine transmitted via the pattern or reference. This setup contains ADG633 single-pole, double-throw (SPDT) switches within the transimpedance amplifiers, which permit for the choice between two completely different features. The output voltage is then sampled by the ADC, which relays the digital knowledge to an FPGA that performs digital demodulation.
The twin-channel setup calculates the ratio of sunshine absorbed by the liquids in each the pattern and reference containers throughout three completely different wavelengths. This key measurement underpins a variety of chemical evaluation and environmental monitoring instruments that assess concentrations and characterize supplies by way of absorption spectroscopy.
As an alternative of utilizing synchronous detection {hardware} as outlined in CN-0312, this circuit captures time-sampled knowledge and employs an FPGA for digital synchronous detection. The FPGA additionally generates the AC excitation sign that powers the LEDs, and a numerically produced sine wave synchronizes with this sign by way of a digital phase-locked loop. The enter sign is then multiplied by this digital sine wave and a model shifted by 90 levels, yielding two low-frequency indicators that demodulate in-phase and quadrature elements of the enter sign on the modulation frequency. The magnitude calculation entails taking the sq. root of the sum of the squares of those two elements.
ADI has examined this reference design. It comes with a invoice of supplies (BOM), schematics, meeting drawing, printed circuit board (PCB) structure, and extra. The corporate’s web site has extra knowledge concerning the reference design. To learn extra about this reference design, click on right here.
