What are the main causes for the uncertainty on digital multimeters?
The individual design of a digital multimeter varies from manufacturer to manufacturer. However, all digital meters use logic circuitry to measure the values that they are displaying. The digital logic circuits, of these devices, may be referred to a ‘gate and timer’ circuits. For example, a ‘square wave’ high frequency signal is ‘gated -on’, or into the component (being measured), by an astable switch (with a lower frequency square wave signal) and then ‘counted’ by ‘edge sensitive’ logic components for the length of the ‘gating’ square wave. The counted result is then ‘gated’ or updated to the display. The process of counting square waves and then updating the results means that the digital meter has a slight time delay built into it and, furthermore, the displayed result reflects the number of pulses counted during each cycle of measurement. The circuit behaviour of inductors, capacitors and even resistors to high frequency signals depends upon the frequency of the ‘reference’ or ga
