Digital electronic meters

The digital electronic meter or DEM indicates the quantity in a numerical display form. In analog meters quantity is measured by the pointer and scale. There are two main types: Digital voltmeter (DVM) and Digital multimeter (DMM). DVM is superior to analog meter in terms of accuracy. It gives accuracy of better than 0.005 % whereas in analog meters accuracy is about 0.5%. Human error in the form of parallax or misreading can be eliminated if we use digital meters. We can take more readings using digital meters in a stipulated time. This is important when we have time constraints. Digital meters possess more precision and automatic ranging possible here. Automatic ranging and polarity features protect it from overloading hazards. Digital meters can be connected to computers directly.

Digital voltmeter

This device use analog to digital converters and BCD counters. Here voltage input signals are converted to binary coded decimal digital words which are used to drive digital display devices. A simple and economical digital voltmeter will have the lowest resolution which is expressed as the number of digits in the display. This device usually uses integrating voltage to frequency converters and thus analog to digital conversion is performed. An example is digital panel meter. For greater resolution, dual-slope converters are used. Dual slope converters are noise resistant but relatively slow. If more than 30 conversions per second task have to be performed, then successive approximation analog to digital converters are used. Using this model, we can perform task up to 1000 readings per second.

Digital multimeters

A dual slope analog to digital converter or voltage to frequency analog to digital converter is used for building a digital multimeter. Wide range of measurement possible here since we are using an input voltage divider for scaling the input voltage. Here resolution is good. A rectifier is included in the circuit to make the measurement of ac voltages possible. While carrying out current measuring function, extra care should be given to allow excessive current through a resistor. Three types of digital multimeters exist in the market: They are laboratory, bench systems and handheld systems. Laboratory and bench type systems use interface tools like IEEE-488 bus or RS 232 to connect to computer. We can interface and perform more tasks with the virtual instrument softwares like LabVIEW.