autoranging

Autoranging is a feature in measurement instruments that automatically selects the most appropriate measurement range or scale for a given input signal. It aims to maximize resolution while protecting the instrument from overload and simplifying use for the operator.

In digital multimeters, autoranging rapidly evaluates the input signal across different input ranges using attenuators and shunt resistors, then selects the range that yields the best resolution without saturating the ADC. The instrument may measure on a high range and shift to a lower range if necessary, then re-measure to display the result. Some meters perform continuous auto-ranging on each sample, while others perform range detection only when a measurement is initiated. Users can usually override the automatic range with a manual range setting or select a fixed range for calibration purposes.

In oscilloscopes, the feature is commonly called autoscale or auto scale. The scope analyzes the waveform and automatically sets the vertical scale (gain), horizontal timebase, and trigger settings to fit the signal within the display. Some models also auto-select probe attenuation and offset to optimize visibility and accuracy.

Advantages of autoranging include convenience, better use of the instrument’s resolution, and protection against input overload. Limitations can include slower measurements due to range switching, potential display jumps during range changes, and reduced control for high-precision or calibration-sensitive work. Many instruments offer both auto-ranging and manual range options, allowing users to lock in a range when needed.