What is Capacitance Meter : Circuit and Its Working

The device like capacitance meter is used to measure the capacitance. This meter is invented by Ewald Georg Von Kleist (10 June 1700) and Pieter Van Musschenbroek (16 March 1692) in 1975. The components used to design capacitance is called capacitors that can be used almost in all electronic devices to store electrical charge. The capacitor with a large capacitance will store more charge. There are different type of capacitance meters are available which allows you to measure the capacitance directly between 0.1 Pico farad and 20 microfarads. The unit of capacitance is farad represented by a letter ‘F’. There are several methods to measure the capacitance but the most accurate method is the bridge method. This article discusses an overview of the capacitance meter.

What is Capacitance Meter?

Definition: The capacitors are very common in basic components in any electronic device, it’s a passive two-terminal electronic component they can store energy in the electrical field and the capacity of the capacitor is a capacitance. The capacitance meter is one type of electronic test instrument used for measuring the capacitor in farads. There are several methods to measure the capacitance but the most accurate method is the bridge method.


Capacitance Meter Working Principle

At the measured capacitance, the reference excitation voltage is applied for the measurement. In the below figure the unknown capacitance is amplified by the amplifier. The block diagram of the capacitance meter is shown in the below figure.

Block Diagram of Capacitance Meter
Block Diagram of Capacitance Meter

The block diagram of capacitance meter (CM) consists of an amplifier, unknown capacitance, reference voltage generator, clock reference, multiplexer, charge amplifier and generators, integrator and comparator. The charge amplifier, charge generator X16, and the charge generator X1 are summed and given to the integrator.

The integrator output is given as input to the comparator, what the comparator does means it monitors the integrator and controls the charge generators X1 and X16 to keep the output of the integrator at 0V. The excitation generator and charge generator X1 both use voltage reference.

Linear Capacitance Meter Circuit using 555IC

The IC 555 timer is used to generate square waves with the desired frequency and desired duty cycle and is also used for other purposes. The two op-amp’s, transistor (which acts as a switch) and potential divider (the three resistors are connected in series is a potential divider). The one end of potential divider provides supply voltage and another end is grounded, the three resistances in potential divider are equal.

PCBWay

The voltage VC is connected to a capacitor, which can charge or discharge periodically. The one terminal of the capacitor is connected to ground and the other terminal can get charge or discharge. The internal diagram of the IC555 timer linear capacitance meter circuit is shown below.

Linear Capacitance Meter Circuit
Linear Capacitance Meter Circuit

The two operational amplifiers in IC555 timer have two input terminals, the output of the first op-amp is 1 (logical) when VC greater than 2/3 V and the second op-amp output is 1 when VC is less than V/3. The two op-amps are connected to SR flip-flop. In a flip-flop, the Q will be ‘1’, when VC goes above 2v/3 similarly the Q will be ‘0’ when VC goes below v/3.

If VC lies between 2v/3 and v/3 (2v/3> VC >v/3) then ‘Q’ value will not change, because the outputs of op-amps are zero when the VC lies between those two values. Most of the things, the operational amplifiers, potential divider, transistor, SR flipflop are actually inside the IC555 timer. The plots of VC and Q are shown in the below figure.

Charging-and-Discharging-Plots
charging-and-discharging-plots

ON-and-OFF Time from the Plots

Charging Time: VC=V/3 + 2V/3(1-e – t1/(RA+RB)C)

Where VC is the voltage across the capacitor

V/3 is the starting point

2V/3 is the target increment

Time constant (τ) = (RA+RB)*C

When charging is finished, e – t1/(RA+RB)C=1/2

e t1/(RA+RB)C = 2

t1*(RA+RB)*C=ln2

t1*(RA+RB)*C=0.693

t1=0.693*( RA+RB)C

Discharge Time: VC = 2V/3 e-t2/RB*C

At time t2, 2V/3* e-t2/RB*C= V/3

Then e-t2/RB*C=1/2

et2/RB*C=2

t2/RB*C=ln2=0.693

t2= RB*C (0.693)

This is how IC555 timer works. The basic circuit for the capacitance meter is shown in the below. Take a capacitor and charge it up to a fixed voltage ‘V’ and connect the other end to the ground.

Basic Capacitance Meter
Basic Capacitance Meter

When K is at P1, the C is charged with Q=CV

When K is at P2, the C is discharged with Q=CV

The charge that flows through the meter every second =f*Q

The average current through the meter = f*Q = f*C*V

The reading of the meter = f*C*V, when f and V are constant the meter reading is linearly proportional to the capacitance of the capacitor.

We know that the charge (Q) = CV if we apply fixed voltage then the amount of charge that the capacitor will hold, that depends on the capacitance value of the capacitor. If the capacitance is more, the charge will be more.

Maintenance of the Capacitance Meter

The maintenance of this meter is

  • The meter should keep away from water and dust
  • Don’t use the meters at high temperatures
  • Don’t use the meters at strong magnetic places
  • Don’t use the liquids or detergents to wipe the meters

Features

The features of digital capacitance meter are

  • Easy to read the measuring values
  • High accuracy
  • Under the strong magnetic field also the measurements are possible
  • Highly reliable
  • Highly durable
  • Lightweight

Digital Capacitance Meter Specifications

The specifications of the digital capacitance meter are

Display: LCD

Range: The range of the digital meter is from 0.1 PF to 20 mF

Battery: 9 volts and the battery life of the alkaline battery is approximately 200hrs and zinc-carbon battery life is approx. 100hrs

Operating temperature: The operating temperature of the digital CM is 00C to 400C

Operating humidity: The operating humidity of the digital CM is 80% MAX.R.H

Advantages

The advantages of the capacitance meter are

  • Hardware requirements are less in Arduino based capacitance meters
  • Simple construction
  • Small in size
  • Less weight

FAQs

1). How is capacitance measured?

Most of the electronic devices contain a capacitor to store electrical energy. The storing ability of a capacitor is known as capacitance which is measured in Farad (F).

2). What is the best capacitor tester?

One of the best capacitor testers is Honeytek A6013L, its range is from 200 Pico farad to 20 microfarads.

3). What instrument measures capacitance?

The LCR meter is one type of electronic test instrument used to measure the capacitance of electronic components.

4). What is capacitance equal to?

The capacitance is equal to the ratio of charge and voltage. It is expressed as C=Q/V.

  • Where C is the capacitance
  • Q is the charge stored, measured in coulombs (C)
  • V is the voltage across the capacitor, measured in volts (V)

5). What is Q capacitance?

The ratio of the reactance of the capacitor (XC) and the effective resistance (R) is defined as a quality factor capacitance or Q capacitance. It is expressed as Q=XC/R.

In this article, the overview of capacitance meter, linear capacitance meter using IC555 timer, features, advantages, specifications, and maintenance of this meter is discussed. Here is a question for you, what is the difference between the capacitor and the capacitance?

Add Comment