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DMM block diagram, measuring DC current

Short answer

A DMM block diagram: input, range switch (shunt for current, attenuator for voltage), amplifier, ADC, decoder, display. For DC current measurement, the current passes through a precision shunt resistor; the resulting voltage drop is amplified, digitized by the ADC, and displayed as current.

Draw a block diagram of digital multimeter. Explain how it measures dc current flowing through it.

A digital multimeter (DMM) shows measured quantities as numbers on a digital display.

Block diagram

 Input -> Range switch -> Amplifier / -> ADC -> Decoder -> Display
          (shunt/atten.)   conditioner         driver
                                  ^
               Clock + control logic + reference voltage

Measuring DC current

 I --->--+--[Rsh]--+---> to circuit
         |         |
         +--> V = I x Rsh --> amplifier --> ADC --> display
  1. The multimeter is connected in series with the circuit, so the unknown current I flows through its internal precision shunt resistor Rsh (very low, such as 0.1 Ω to 10 Ω, selected by the range switch).
  2. The shunt converts current into a proportional voltage: V = I × Rsh (Ohm's law).
  3. The small voltage is amplified by the conditioner.
  4. The ADC converts it to a digital number, using a reference voltage.
  5. The decoder and driver show the value as a reading in mA or A.

For a higher current range, a lower Rsh is selected so that the voltage drop is small (burden voltage), with a fuse for protection. Example: for the 200 mA range with Rsh = 1 Ω, 100 mA gives 0.1 V, displayed as 100.0 mA.

✓ Answer checked by Claude Opus 5.5 (high effort)

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