A Digital Multimeter (DMM) is a precision analog instrument used to measure AC and DC voltage, AC and DC current, capacitance, and resistance. Five system level blocks are common to bench DMM designs: Signal Conditioning and A/D conversion of the input signal, LCD/LED/Keypad, Control and Data Processing, Memory/Peripheral devices, and Power Management. Implementation specifics will obviously vary depending on the feature set of the meter.
The common core subsystems are:
Analog Front-End
Signals are initially passed through a signal conditioning subsystem which amplifies or attenuates the analog signal in preparation for further conditioning, depending on whether the measurement is AC volts, DC volts, current, or resistance. Precision amplifiers and analog to digital converters are used to facilitate resolutions from 5 1/2 to 8 1/2 digits on modern DMMs.
LCD/LED/Keypad
Bench DMMs offer dual, 7 segment displays. The PC is typically used to provide a full-featured graphical user interface for bench DMMs.
Control and Data Processing
Executes measuring processes and controls interface with memory and peripheral devices. The Digital Signal Processor (DSP) is used to linearize data from the ADC and perform calibration. It also performs real-time analysis of acquired signals such as min/max, averaging, and conversion to engineering units. Modern DMMs allow users to directly measure temperature using a variety of sensors.
Memory/Peripheral Devices
Measurement results are stored in EEPROM or FLASH memory and can be uploaded to a PC via USB, Ethernet, RS-232, or IEEE-488 (GPIB) interfaces.
Power Management and Conversion
Converts the input battery power to run various functional blocks. TI has a wide range of products like amplifiers, ADCs, Power, Interface, and Processors to meet the requirements of bench Digital Multimeter designers.
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