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Handheld Digital Multimeter

Instrumentation & Measurement Solutions -
Handheld Digital Multimeter

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Multimeters are mainly used to measure resistance, as well as DC/AC voltage and current. Common multimeters can be divided into two types, desktop and handheld digital multimeters depending on their sizes. Desktop digital multimeters are usually used in labs for high-precision measurement and instrument calibration. Handheld digital multimeters are battery-powered devices, often used for on-site debugging. In recent years, handheld digital multimeters have gained tremendous improvement in measurement precision.

A handheld digital multimeter is basically composed of Analogue Front End (AFE), MCU, Human-machine interface and Power supply. The design of handheld multimeters should focus on the features of low power, high performance and compact size.

 

After a measurement function is selected by the switch, the AFE can start to collect input signals and convert them into digital signals in order to feed into the MCU for processing. http://uk.farnell.com/jsp/bespoke/bespoke7.jsp?bespokepage=common/en/technology-first/applications/instrumentation-measurement/handheld-digital-multimeter.jsp#When measuring resistance, the AFE provides a proper current generated by the inside resistance I-source so that the voltage detected on the measured object is within the input range of the ADC. The detected voltage is amplified and converted into digital signals for data processing by MCU.

  • When measuring AC current, a current shunt is selected to convert the AC current flowing through it into AC voltage. This voltage is converted by the RMS-to-DC converter into a DC voltage, which is then amplified and converted into digital signals for data processing by MCU.
  • When measuring DC current, another current shunt is selected to convert the DC current flowing through it into a DC voltage. The DC voltage is then amplified and converted into digital signals for data processing by MCU.
  • When measuring AC voltage, high voltage input is attenuated while low voltage input remains unchanged. And then it is converted by the RMS-to-DC converter into DC voltage, which is then amplified and converted into digital signals for data processing by MCU.
  • When measuring DC voltage, high voltage input is attenuated while low voltage input remains unchanged. And then it is amplified and converted into digital signals for data processing by MCU.

The MCU controls measurement processes and implements real-time calculations such as averaging and unit conversion for sampled data. The human-machine interface generally includes a display, several functional keys and a switch for selecting measurement functions. An entry-level handheld digital multimeter usually uses a 7-segment LCD, while a high-end multimeter may have a 1/4 VGA OLED. An isolated power supply is adopted in this solution to implement battery management and power conversion to drive different functional blocks.

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