The hardware structure is shown in Fig. 1 (not preserved in the web version). Sensors pick up the measured quantity and convert it to an electrical signal; after filtering, a multiplexer feeds each channel in turn, under single-chip control, into a programmable-gain amplifier; the amplified signal is A/D-converted into the microcontroller, which computes and processes per instrument settings (e.g. nonlinearity correction) and drives display and printing; comparing results with parameters stored in on-chip Flash or E²PROM, it outputs control signals — alarm triggers, relay contacts and the like. Smart instruments can also form distributed measurement-control systems with a PC: the microcontroller as the lower unit collects measurements and data, passing them over serial links to the PC for global management.
With microelectronics advancing, very-large-scale single-chip microcomputers appeared, integrating CPU, memory, timers/counters, parallel and serial interfaces, watchdogs, preamplifiers, even A/D and D/A converters. Centred on the microcontroller, computer and measurement-control technology merge into the "intelligent measurement-control system" — the smart instrument.
Compared with traditional instruments, smart instruments offer:
In the 1980s microprocessors entered instruments; front panels went keyboard-oriented; measurement systems linked over IEEE-488; and personal instruments, unlike traditional standalone ones, developed.
In the 1990s instrument intelligence showed in: microelectronics deeply influencing instrument design; DSP chips greatly strengthening digital signal processing; microcomputers giving stronger data processing; ubiquitous image processing; and wide VXI-bus adoption.
Recently smart measurement-control instruments have flourished. Domestic examples include smart throttling flowmeters with automatic differential-pressure compensation, multi-segment program-temperature controllers, smart controllers realising digital PID and complex control laws, and smart chromatographs analysing and processing spectra.
International varieties are richer: Honeywell's DSTJ-3000 smart transmitters compound-measure differential pressure with automatic compensation of body temperature and static pressure, accurate to ±0.1% FS; RACA-DANA's 9303 ultra-low-level meter uses a microprocessor to remove resistor thermal noise, measuring down to -77 dB; FLUKE's 5520A multi-function calibrator carries three microprocessors with 1 ppm short-term stability and 0.5 ppm linearity; FOXBORO's digital self-tuning controller applies expert-system technology to tune like an experienced control engineer from field parameters — ideal for frequently changing or nonlinear processes, keeping the whole loop at its best through automatic tuning.
Micro smart instruments combine microelectronics, MEMS and information technology in small, fully featured packages, performing acquisition, linearisation, DSP, control output and amplification, instrument interfacing and human interaction. As MEMS matures and prices fall, applications widen — beyond traditional roles into automation, aerospace, military, biotechnology and medicine. Where a patient once needed several tubes for measuring and controlling several parameters — risking infection — micro smart instruments measure multiple parameters in implantable form.
Multifunction is itself a hallmark. For fast, complex digital system design, makers built function generators combining pulse generation, frequency synthesis and arbitrary waveform generation — outperforming dedicated pulse generators and synthesisers in accuracy and offering better solutions across test functions.
