Explain to the digital voltmeter


Welcome to everyone, dear readers. We all know what the digital voltmeter machine is all about. Someone else may have used it. We know about its use but we do not know how it works. So today we’ll know exactly how a digital voltmeter works.


Basic transistor voltmeter configuration:

The following figure shows a Balanced Bridge transistor voltmetar circuit. In this, the internal resistance of the collector of T1 and T2 transistors and the bridge circuits formed by RL1 and RL2 load resistance. The base of T2 is grounded by preventing Rb2. If needed, one more resistance series can be given. On the basis of T1 the input voltage is to be applied by Rb1 which is to be measured.

A variable resistor is connected via R2 to the emitter of T1 and T2. Vee is applied to the emitter through R1 and R2. Vcc is the transistor’s gasping voltage when the input current for the Vee and Vcc flows when no voltage is applied in the input. Now, if the positive voltage is applied on the base of T1, its base current flows. So collector and emitter current increases. Increased voltage drops in R1 decreases the emitter current due to T2. So the bridge becomes unbalanced. The current flows through the PMMC in proportion to the change in the input voltage. Proportional voltage of that current is calibrated in PMMC.


  1. Less time takes less time to read.
  2. Power consumption is very low.
  3. Size is low in size and light.
  4. Convenient to use in battery operated instruments.
  5. The structure is very strong.
  6. Relatively stable.


  1. Input impedance less than other electronic voltmers.
  2. High voltage can not be used.
  3. The DC as input of tvm is to be applied. So if the AC measurement is required, then use the Rectifier Circuit.
  4. Where the temperature changes too much, the error of the reader changes to the transistor’s characteristic.

Types of digital voltmeter

  1. Ramp type Digital Voltmeter.
  2. Integrating Digital Voltmeter.
  3. Continues balance Digital Voltmeter.
  4. Approximation Digital Voltmeter.


Ramp Type Digital voltmeter:

Ramp type Digital voltmeter measures the time required to increase the linear ramp voltage “0” to the input level or to decrease the level level input voltage to “0”. The time is calculated through an electronic time counter. The counting counters are displayed on electronic inducting tubes or display systems.

At the starting bicycle, the ramp generator uses the ramp voltage between the operators. Ramp voltage can be both positive or negative types. This ramp voltage measurement is consistently compared to the input voltage with the input compatator. Initially, the ramp voltage is equal to the input voltage. As a result, a pulse in the output of the comparteter is created which will open the gate circuit. When using negative ramp voltage, it decreases until it is zero and Ground

Compartor starts the gate circuit. At this time, the Oscillator passes through the gate by creating Clock Pulse and handles several decode counters. Decimal numbers are displayed on indicator tunes or display systems. The samplerate material is determined by measuring the bicycle which is applied to the Ramp generator and the Ramp voltage is made. At the end of the measurement, the ramp generator again produces a reset pulse and the decidged counting unit is taken down to the low state and the display system is off.



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