Multimeters are widely used for to measure Voltage, resistance, Alternating Current, Direct Current, transistor HFE, continuity etc… Previous days we used analog type meters to measure electronic parameters. Analog type meters are has unique circuit and moving mechanism and measuring scale hence we cannot use one analog type meter to measure several electronic parameters like voltage, current, resistance etc… but thanks to digital multimeter which enable us to measure many things in electronics with simple single handheld device.
Many multimeters in the market comes with several features to measure parameters in electronics. Here we can ask our self “how this single device measures many things?”
Every common multimeter has one printed circuit board (main board), LCD display unit, Measuring probes (normally RED for +ve and BLACK for –ve) and power source. When we measuring AC (Alternating current) voltage this multimeter limits AC voltage and converts into DC after that takes samples with the help of analog to digital converter (ADC) those sampled value of measured inputs are displayed by LCD with the help of LCD controller. By the same way measurement of DC (Direct current) also goes.
If we are measuring Resistance or continuity the multimeter gives around 1.2Volt to 3Volt through measuring probe as series path. Sample & hold unit and ADC unit are measures the return voltage and calculates value, after that LCD displays the value. If the value goes beyond the selected range means the Chip drives the LCD display to show maximum as one at the left most digits.
COB : Chip on board
In a multimeter you can spot the black colour module. That is called COB (Chip On Board) it contains Sample & Hold unit, Analog to Digital converter(ADC), LCD controller, and little memory (in some model of multimeters). This COB is responsible for many parameter measurement in electronics.