Virtual Multimeter (virtual multimeter)

By combining digital multimeter features with plug-in board technology the capabilities of digital multimeters has been extended to produce a range of computer-based digital multimeters, known as virtual multimeter (virtual multimeters). As modern instruments, virtual multimeters fulfill the need for enterprise-wide measurements, but still provide the sophisticated measurement capabilities of traditional digital multimeters. Performing the same basic functions are traditional digital multimeters, virtual multimeters measure voltage (A.C. and D.C.), current, and resistance.

digital multimeters and virtual multimeters can be evaluated on

(i) a variety of features, such as accuracy, resolution, reading rates, and measurement ranges
(ii) additional functions, such as frequency, period, temperature, minimum/maximum, and diode test
(iii) math capabilities, such as relative, percent, or standard deviation readings.

Construction and Working

A basic block diagram of virtual multimeter is shown in Fig.3.15. All digital multimeters and virtual multimeters share the same architecture. The architecture is divided into three main components namely, front-end signal conditioning. Analog-to-digital (A/D) converter, and processor and display. Like traditional digital multimeters, virtual multimeters have front-end analog measurement circuitry to interface to real-world signals.

The A/D converter inside the virtual multimeter converts analog input signals to digital values. It is the primary component that affects reading speed, resolution, accuracy, and normal-mode rejection. Sophisticated virtual multimeters are multi-slope integrating A/D circuits or sigma-delta A/D converts to achieve high resolution and accuracy. A hardware A.C. conversion circuit is built on the dedicated multimeter boards in the signal-conditioning front end to convert A.C. signals to D.C. voltages to be measured by the A/D converter. The A.C. converter may be either an averaging type or a True-rms (Trms) converter. Both averaging and Trms converters will give the same output for sine waves, but signals other than sine waves produce an error when measured with an average-based meter. For irregular waveforms, a Trms converter gives more accurate results. virtual multimeters built with general-purpose A/D boards, do not have specialized hardware A.C. conversion circuitry. Rather, they use software-specialized hardware A.C. conversion circuitry. Rather, they use software-based Trms A.C. conversion algorithms that execute on the computer itself.

virtual multimeters and digital multimeters offer a variety of measurement ranges. Common measurement ranges include 20 mV, 200mV, 2 V, 25 V, and 250 V front-end signal conditioning amplifiers and attenuators scale the input signal for a particular range setting. By scaling the input signal as close to full range as possible, virtual multimeters/digital multimeters get the greatest resolution and accuracy.

Advantages of Virtual Multimeter (virtual multimeter)

Following are the advantages of virtual multimeters (virtual multimeter):

(i) Many of the advanced features of digital multimeters can be implemented easily by any user of a virtual multimeter, as opposed to being limited to the fixed functionality of the particular digital multimeter model being purchased from a particular vendor.
(ii) Accessories such as high-voltage probes, current shunts, clamp-on-current probes, thermistor probes, thermocouple probes, and multiplexing/scanning options increase virtual multimeter versatility even further.
(iii) Using virtual multimeter, both development time and expense are saved as automated test and measurement applications are quickly and easily implemented.