Dual Slope Integrating Type DVM Working – Block Diagram | New Topic

In this note, we are going to know about Dual Slope Integrating Type DVM Working, Block Diagram, Advantages, and Applications as well. Welcome to Poly Notes Hub, a leading destination for engineering notes.

Author Name: Arun Paul.

What is Dual Slope Integrating Type DVM?

A Dual Slope Integrating Type Digital Voltmeter (DVM) is a type of integrating voltmeter with excellent accuracy and noise rejection. It is commonly employed in precision measurement applications because of its ability to eliminate mistakes caused by noise and fluctuations.

Specifications of Dual Slope Type DVM

• The input voltage ranges from millivolts to few volts.
• It has high accuracy, often better than 0.01%.
• The resolution can range from 3½ to 6½ digits.
• It is operates on low-voltage DC power, often around ±5V or ±15V.
• This device has high input impedance to prevent loading effects on the measured circuit.

Dual Slope Integrating Type DVM Block Diagram

Here is the block diagram of dual slope integrating type DVM –

• Input Signal: The unknown DC voltage to be measured is fed into the circuit.
• Integrator: This stage includes an operational amplifier (op-amp) with a capacitor in the feedback path. When the input voltage is applied, the integrator produces a linearly increasing voltage over a set time period.
• Comparator: The integrator’s output is compared to a reference voltage to determine when it passes zero.
• Control Unit: A timing circuit regulates the integration and de-integration phases by switching the reference voltage.
• Counter: A digital counter measures the time it takes for the integrator to return to zero and turns it into a digital value.
• Display Unit: The digital output of the counter is shown on a 7-segment LED or LCD.

Dual Slope Integrating Type DVM Working

A dual slope integrating digital voltmeter operates in two phases: integration and de-integration.

During the integration phase, an unknown DC voltage is applied to the integrator circuit for a predetermined time T. The integrator is made up of an operational amplifier with a capacitor in its feedback route. As the input voltage is applied, the integrator begins to accumulate charge, resulting in a linear increase in output voltage. The slope of this ramp is directly proportional to the size of the applied voltage. This phase lasts for a set amount of time, ensuring that any noise or oscillations in the input signal are averaged out, resulting in improved accuracy.

Following the integration period, the circuit enters the de-integration phase, which involves disconnecting the input voltage and applying a known reference voltage with the opposite polarity to the integrator. The capacitor begins to discharge at a steady pace, and the integrator output voltage decreases linearly. A digital counter measures the time it takes for the output to return to zero. Because the discharge rate is proportional to the reference voltage, the de-integration phase lasts exactly as long as the input voltage does.

Finally, the conversion and display procedure occurs. The counter processes the measured de-integration time and converts it to a corresponding digital value. The result is then shown on a seven-segment LED or LCD screen, giving a precise reading of the input voltage. The dual slope technique offers great precision by removing mistakes caused by noise and component changes, making it an excellent choice for applications that require accurate voltage readings.

Important Equations for Dual Slope Integrating Type DVM

A. Voltage-Time relationship during integration –

Where;

• V_out​(t) is the integrator output voltage
• R and C are the resistance and capacitance in the integrator circuit
• Vin​ is the applied input voltage
• T is the fixed integration time

B. Integrator Output After Time T –

C. Time required to de-integration –

Where;

• Where t_d​ is the de-integration time
• V_ref​ is the known reference voltage

D. Final Digital Output (Measured Voltage Calculation)

• The input voltage is determined based on the ratio of de-integration time t_d​ to integration time T.

Dual Slope Integrating Type DVM Advantages

Here we have listed some advantages of dual slope type DVM –

• It has high accuracy. So, the measurement is more stable than other type of instrument.
• It rejects AC noise, such as 50 Hz or 60 Hz power line interference.
• This device is capable of measuring small voltage variation as well.
• Unlike some other conversion techniques, this method does not require highly matched components.
• Used in many precision measurement applications like weight scale, bio-medical applications etc.

Dual Slope Integrating Type DVM Applications

Here we have listed some applications of dual slope integrating type DVM –

• Used in high-precision digital multimeters.
• Commonly used in voltmeters for research and testing.
• Employed in automated testing and process control.
• Used in digital weighing machines for accurate weight measurement.
• Utilized in devices like ECG monitors for precise voltage readings.