The Q-meter is an instrument designed for the measurement of Q-factor of the coil as well as for the measurement of electrical properties of coils and capacitors. -This instrument operates on the principle of series resonance i.e. at resonate condition of an ac series circuit voltage across the capacitor is equal to the applied voltage times of Q of the circuit. If the voltage applied across the circuit is kept-constant then voltmeter connected across the capacitor can be calibrated to indicate Q directly.
If a metal wire or conductor is stretched or compressed its resistance changes because of change in length, change in resistivity and change in cross sectional area. This effect is called piezoresistive effect. The cantilever used in the primary elastic transducer of force measuring system, where a known mass is attached to cantilever, the unbalanced voltage, can be calibrated in terms of either force or weight.
The calibration is the process for determining the correct values of mesurand by compared with the standard ones. The potentiometer is extensively used for a calibration of voltmeter and ammeter .The procedure for standardization of the potentiometer is illustrated by the following example.
hermocouple transducer is widely used in industrial applications for temperature measurement. Thermocouples active transducer because there is no need of voltage source and transducer bridge circuitry. The working principle of the thermocouple is explained below: -When two dissimilar metals A & B are together to form a closed circuit and the junctions J1 and J 2 are kept at two different temperatures T 1 and T 2 then an e.m.f. is gene rated resulting flow of current in the loop or circuit. The two junctions in the loop are reference or cold junction which is generally kept at 0 0C and the other is hot junction at which the temperature is measured.
This type of transducer is used for temperature measurement. Here the basic concept used is that electrical resistance of different metal changes in accordance with the temperature i.e. for temperature measurement. Principle used is that the resistance of a conductor changes in proportion with the change in temperature. The unknown temperature is determined in terms of electrical resistance of the conductor, which senses the temperature. The change in resistance of this device is precisely determined either by bridge circuit or by ohmmeter. Resistance of a conductor changes with change in temperature. This property is used for the measurement of temperature and each transducer is called Resistive Thermometer and falls in the category of electrical resistive transducer. The variation of resistance ‘R’ with temperature ‘T’ can be presented as:
LVDT stands for linear variable differential transformer. It works on the principle of mutual induction LVDT illustrated in figure consist of three symmetrically spaced coils bound out and illustrated bobbin. A magnetic core, which moves through the bobbin, provides a path for magnetic flux linkage between coils. The position of the magnetic core control the mutual inductance between the primary coils and two secondary coils.
Ultrasonic is defined as that band above 20 KHz. It continues up into the MHz range and finally, at around 1 GHz. Ultrasonic sensors (also known as transducers when they both send and receive) work on a principle similar to radar or sonar which evaluate attributes of a target by interpreting the echoes from radio or sound waves respectively. Ultrasonic sensors generate high frequency sound waves and evaluate the echo which is received back by the sensor. Sensors calculate the time interval between sending the signal and receiving the echo to determine the distance to an object. Ultrasonic sensors are active, visible, volumetric sensors.
Wein Bridge is used as an AC Bridge. This is used to measure frequency. Wein Bridge is used as a notch filter in the harmonic distortion analyzer, also used in audio and high frequency oscillators as the frequency determining element.
The Wein Bridge used for the measurement of frequency is shown in this bridge has a series RC combination in one arm and a parallel RC combination in the adjoining arm.
→ Measure unknown inductance capacitance resistance using following bridges (a) Anderson Bridge (b) Maxwell Bridge
THEORY:-Actually this bridge is the modified Maxwell inductor capacitance bridge. In this bridge double balance can obtained by fixing the value of capacitance and changing the value of electrical resistance only. It is well known for its accuracy of measuring inductor from few micro Henry to several Henry. The unknown value of self inductor is measured by method of comparison of known value of electrical resistance and capacitance. In this method, the self-inductance is measured in terms of a standard capacitor.
To understand the operation of a solar cell, we need to consider both the nature of the material and the nature of sunlight. Solar cells consist of two types of material, often p-type silicon and n-type silicon. Light of certain wavelengths is able to ionize the atoms in the silicon and the internal field produced by the junction separates some of the positive charges ("holes") from the negative charges (electrons) within the photovoltaic device. The holes are swept into the positive or p-layer and the electrons are swept into the negative or n-layer. Although these opposite charges are attracted to each other, most of them can only recombine by passing through an external circuit outside the material because of the internal potential energy barrier. Therefore if a circuit is made power can be produced from the cells under illumination, since the free electrons have to pass through the load to recombine with the positive holes.
THEORY:-The 3 point method fall of potential ground resistance test requires complete isolation from the power utility. Not just power isolation, but also removal of any neutral or other such ground connections extending outside the grounding system. This test is the most suitable test for large grounding systems and is also suitable for small electrodes
When large currents are to be measured, it is usual to use low range ammeters with suitable shunts, in DC circuits but since this is neither convenient nor practical to use this method with AC current, current transformers are employed, which are specially constructed accurate ratio instruments in conjunction with standard low range AC instruments. There purpose is to reduce the line current to a value small enough to be measured with meters of moderate rise and capacity. In other words CT‟s are used for extending the range of AC ammeters. The current transformer has a primary winding of one of more turn of thick wire connected in series with the line carrying the current to be measured. The secondary consists of a large no. of turn of fine wire & feeds a standard 5A ammeter or he current coil of a wattmeter or watt hour meter. Since the ammeter resistance is extremely low, a CT operates with it secondary under nearly short circuit condition.
- Connections are made as per the circuit diagram.
- Arrange the values of the resistances R1, R2, R3 and R4 so that the condition R1/R3 = R2/R4 is satisfied.
- Apply a sinusoidal signal of fixed amplitude and fixed frequency of 1 KHZ using A.F. generator (A.F.O) between terminals A and C.
- The Capacitance value of C2 is varied to obtain bridge balance condition. i.e., At this condition minimum sound is heard from head phones or ear phones.
- Note down the values of R1, R2, R3, R4 and C2 in the table.
- Repeat the same procedure for different sets of values of R1, R2, R3, R4 and C2
- Calculate the unknown capacitance using the formula given in the table