Twin-Channel Colorimeter Reference Design

The design encompasses a modulated gentle supply and digital synchronous detection for precision in chemical evaluation and environmental monitoring.

A dual-channel colorimeter is a necessary software in each scientific analysis and industrial purposes, prized for its enhanced measurement accuracy and reliability. This instrument operates by using two separate channels—one to investigate 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) geared up 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 a typical 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 gentle supply, successfully eliminates noise at frequencies totally different from the modulation frequency, enhancing accuracy. The system measures the ratio of sunshine absorption in pattern and reference containers at three distinct wavelengths, a vital operate in numerous chemical evaluation and environmental monitoring instruments that make the most of absorption spectroscopy to find out materials concentrations and traits.

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A clock, set to a user-defined frequency, modulates one of many three LED colours utilizing a relentless present driver that comes with the AD8615 op-amp, the ADG819 change, and the AD5201 digital potentiometer. A beam splitter divides the emitted gentle, directing half by the pattern container and the opposite half by 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 by 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 totally different beneficial properties. The output voltage is then sampled by the ADC, which relays the digital information 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 totally 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.

– Commercial –

As a substitute of utilizing synchronous detection {hardware} as outlined in CN-0312, this circuit captures time-sampled information 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 parts of the enter sign on the modulation frequency. The magnitude calculation includes taking the sq. root of the sum of the squares of those two parts.

ADI has examined this reference design. It comes with a invoice of supplies (BOM), schematics, meeting drawing, printed circuit board (PCB) format, and extra. The corporate’s web site has extra information concerning the reference design. To learn extra about this reference design, click on right here.