Overview
A precision measurement system must recover a small sensor signal and digitize it without adding noise, offset or drift, and the result depends on the whole chain rather than on one part. ADI provides the building blocks - an instrumentation amplifier for the first stage, a zero-drift amplifier for the precision gain, a converter for the digitization and a low-noise regulator for the supply - and BeiLuo supplies them with genuine traceability and FAE support. This page shows how the parts fit together in a precision measurement design.
The Input Stage
The first stage sets the noise and the common-mode performance of the chain. A bridge or a thermocouple produces a small differential signal riding on a common-mode voltage, so an instrumentation amplifier such as the AD8221 recovers it with a high common-mode rejection and a single-resistor gain. The low input current keeps the error small with a high source impedance, and the referenced output lets the stage level-shift into the converter. Where the DC accuracy matters, add a zero-drift part such as the ADA4522-2, which holds a microvolt-level offset over time and temperature and removes the slow error that would otherwise dominate a high-gain measurement.
Choosing the Gain
Set the gain so the full-scale sensor signal fills the converter input range, then check the offset, the noise and the drift against the error budget. A single low-drift gain resistor usually sets the gain, and its tolerance becomes part of the overall accuracy, so it deserves care as much as the amplifier.
The Converter
The converter turns the conditioned signal into data. Where the system samples several channels that must stay coherent, such as a three-phase power meter, the AD7606 captures eight channels at the same instant with an integrated reference and anti-alias filter, so the phase relationship is preserved and the external circuitry is small. Where a single fast channel is digitized into the tens of megahertz, the AD9226 provides a pipelined core with a good dynamic performance. The reference, whether internal or external, sets the accuracy, so it is chosen with a low temperature coefficient and a clean decoupling.
Coherent Sampling
Simultaneous sampling preserves the phase between a voltage and a current channel, which a power or a power-factor calculation needs. A multiplexed converter introduces a channel-to-channel delay that distorts the result, so the architecture is chosen from the requirement, not only from the resolution.
The Power Rail
A measurement chain is only as quiet as its supply. A switching regulator such as the ADP5054 delivers the rails efficiently, and a low-noise LDO such as the ADP7118 placed behind it removes the ripple and delivers a clean rail for the converter, the reference and the amplifiers. Keep the converter's reference and analog decoupling close, return the analog ground to a single point and keep the switching node away from the sensitive inputs.
Getting It Right
A precision measurement succeeds when the noise, the offset and the layout are managed together: condition the signal with a high-rejection amplifier, digitize it with the right architecture, power it from a clean rail and keep the grounds disciplined. BeiLuo supplies the whole ADI chain from stock, with the documentation to prove where each part came from and an FAE team that will review the error budget and the layout with you.