---
title: "DMM block diagram, measuring DC current"
subject: "Basic Electronics Engineering"
chapter: 7
key: "semester_2/basic_electronics_engineering:dmm-dc-current"
source: https://www.bctengineer.com/q/semester_2/basic_electronics_engineering/dmm-dc-current
site: BCT Engineering
---

# DMM block diagram, measuring DC current

Basic Electronics Engineering · Chapter 7: Application of Electronic System

- Asked in: 2073 Bhadra, 5 marks
- Video: [Simplest bock-diagram of DMM ||Working of DMM || Block diagram of DMM |](https://www.youtube.com/watch?v=At1C-o3evTM) — Hari Mohan Rai
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/basic_electronics_engineering/dmm-dc-current
- Whole chapter: https://www.bctengineer.com/md/semester_2/basic_electronics_engineering/chapter-7

## Question

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

## 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.

## Answer

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

#### Block diagram

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

#### Measuring DC current

```text
 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.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How is the DMM connected to measure DC current?
   A. In series with the circuit
   B. In parallel across the component
   C. Across the supply with power off
   D. Through an attenuator in parallel
   Answer: A. The current must flow through the meter's internal shunt, so the meter is in series. (Key point: Connection for current)

2. How does the DMM convert current into a quantity the ADC can read?
   A. By passing a constant current
   B. By a voltage divider
   C. By measuring the voltage V = I x Rsh across a precision shunt
   D. By amplifying the current directly
   Answer: C. The shunt resistor produces a proportional voltage drop by Ohm's law, which is amplified and converted. (Key point: Shunt principle)

3. For higher current ranges, the shunt resistor chosen is:
   A. Higher so the voltage is larger
   B. Infinite
   C. Equal to 10 MΩ
   D. Lower so the voltage drop (burden voltage) is small
   Answer: D. A smaller Rsh keeps the burden voltage low at larger currents. (Key point: Shunt value and burden)

## Related in Basic Electronics Engineering

- [DMM block diagram: V, I and R measurement](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Admm-dc-voltage-current-resistance) — Basic Electronics Engineering, chapter 7
- [Short note: Digital multimeter (DMM)](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Ashort-note-dmm) — Basic Electronics Engineering, chapter 7, asked 4×
- [Remote control or digital multimeter](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Aremote-control-or-dmm) — Basic Electronics Engineering, chapter 7

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