Essentials of indicating instruments

In this section we will discuss certain features which are common to all electrical measuring instruments. We will first consider various torques acting on its moving system. In an indicating instrument, it is essential that the moving system is acted upon by three distinct torque (or forces) for satisfactory working. There torques are: 1. A deflecting or operating torque, Td 2. A controlling torque, Tc 3. A dampling torque, Tv. Deflecting (Or the Operating) Torque The deflecting torque, causes the moving system of the instrument to move from its zero position. It may be produced by utilizing any one of the effects of current or voltage in the ins

Read more »

CLASSIFICATION OF MEASURING INSTRUMENTS

Electrical measuring instruments may be classified into two groups: (a) Absolute (or primary) instruments. (b) Secondary instruments. Absolute Instruments • These instruments give the value of the electrical quantity in terms of absolute quantities (or some constants) of the instruments and their deflections. • In this type of instruments no calibration or comparison with other instruments is necessary. • They are generally not used in laboratories and are seldom used in practice by electricians and engineers. They are mostly used as means of standard measurements and are maintained lay national laboratories and similar institutions. • Some of the

Read more »

DEFINITIONS OF IMPORTANT TERMS

Measurement work employs a number of terms which are defined below: Measurand: The quantity or variable being measured is called measurand or measurement variable. Accuracy: It is defined in terms of the closeness with which an instrument reading approaches the true or expected (desired) value of the variable being measured. Precision: It is measure of the consistency of reproducibility (repeatability) of the measurement (i.e., the successive reading do not differ). For a given fixed value of an input variable, precision is a measure of the degree to which successive measurement differ from one another. Sensitivity: It is defined by the change in the

Read more »

Introduction to Measurements

Measurements are the basic means of acquiring knowledge about the parameters and variables involved in the operation of a physical system. Measurement generally involves using an instrument as a physical means of determining a quantity or variable. An instrument or a measuring instrument is, therefore, defined as a device for determining the value or magnitude of a quantity or variable. The electrical measuring insturment, as its name implies, is based on electrical principles for its measurement function. These days a number of measuring instruments, both analog as well as digital ones, are available for the measurement of electrical quantities like

Read more »

Clippers

A circuit which removes the peak of a waveform is known as a clipper. A negative clipper is shown in Figure below. This schematic diagram was produced with Xcircuit schematic capture program. Xcircuit produced the SPICE net list Figure below, except for the second, and next to last pair of lines which were inserted with a text editor. *SPICE 03437.eps * A K ModelName D1 0 2 diode R1 2 1 1.0k V1 1 0 SIN(0 5 1k) .model diode d .tran .05m 3m .end Clipper: clips negative peak at -0.7 V. During the positive half cycle of the 5 V peak input, the diode is reversed biased. The diode does not conduct. It is as if the diode were not t

Read more »

Classification of Clippers

Classification[edit source | editbeta] Clippers may be classified into two types based on the positioning of the diode. [1] Series Clippers, where the diode is in series with the load resistance, and Shunt Clippers, where the diode in shunted across the load resistance. The diode capacitance affects the operation of the clipper at high frequency and influences the choice between the above two types. High frequency signals are attenuated in the shunt clipper as the diode capacitance provides an alternative path to output current. In the series clipper, clipping effectiveness is reduced for the same reason as the high frequency curr

Read more »

Intro-clipper

In electronics, a clipper is a device designed to prevent the output of a circuit from exceeding a predetermined voltage level without distorting the remaining part of the applied waveform. A clipping circuit consists of linear elements like resistors and non-linear elements like junction diodes or transistors, but it does not contain energy-storage elements like capacitors. Clipping circuits are used to select for purposes of transmission, that part of a signal wave form which lies above or below a certain reference voltage level. Thus a clipper circuit can remove certain portions of an arbitrary wavef

Read more »

Second Order Transient Analysis

Second Order Transient Analysis How do recognize it? A transient problem is one that asks you to find voltage (or current) vs. time. It also includes some instant event: a switch opens or closes, the power supply turns on, a part is suddenly pulled out the circuit, a fuse blows. Your answer can either be a formula for v(t) or i(t) or it might be a graph of v or i on the vertical axis and time on the horizontal axis. Second-order problems have two independent energy storage elements (capacitors and/or inductors). Note that two capacitors in parallel or series only count as one capacitor because you can find the equivalent capacitance (same with indu

Read more »

First-Order Transient Analysis

First-Order Transient Analysis How do recognize it? A transient problem is one that asks you to find voltage (or current) vs. time. It also includes some instant event: a switch opens or closes, the power supply turns on, a part is suddenly pulled out the circuit, a fuse blows. Your answer can either be a formula for v(t) or i(t) or it might be a graph of v or i on the vertical axis and time on the horizontal axis. First-order problems have only one energy storage element (either a capacitor or inductor, but not both). Note that two capacitors in parallel or series only count as one capacitor because you can find the equivalent capacitance (same wi

Read more »

Continuity condition of Inductors

Continuity condition of Inductors The current that flows through a linear inductor must always be a continuous. , the voltage across the inductor is not proportional to the current flowing through it but to the rate of change of the current with respect to time,()ditdt. The voltage across the inductor () is zero when the current flowing through an inductor does not change with time. This observation implies that the inductor acts as a short circuit under steady state dc current. In other words, under the steady state condition, the inductor terminals are shorted through a conducting wire. Alternating current (ac), on the other hand, is constantly cha

Read more »

Introduction to Transient Analysis

So far we have considered dc resistive network in which currents and voltages were independent of time. More specifically, Voltage (cause input) and current (effect output) responses displayed simultaneously except for a constant multiplicative factor (VR). Two basic passive elements namely, inductor →→RI=×()L and capacitor () are introduced in the dc network. Automatically, the question will arise whether or not the methods developed in lesson-3 to lesson-8 for resistive circuit analysis are still valid. The voltage/current relationship for these two passive elements are defined by the derivative (voltage across the inductor C()()LLditvtLdt=, where

Read more »

Network Theorms to AC

SUPERPOSITION THEOREM A circuit is linear when superposition theorem can be used to obtain its currents and voltages. When this theorem is applied to an ac circuit, it has to be remembered that the voltage and current sources are in the phasor form and the passive elements are impedances. WORKED EXAMPLE 1: A circuit is presented in Fig. 30. The task is to find the current through the load current, using superposition theorem. The values of components are specified by equation (99). We can find the contribution due to one voltage source, by replacing the other voltage by a short circuit. Only the ideal part of the source is to be replaced by

Read more »

reciprocity theorem.

In many electrical network it is found that if positions ofvoltage source and ammeter are interchanged, the reading of ammeter remains same. It is not clear to you. Let’s explain in details. Suppose avoltage source is connected to a passive network and an ammeter is connected to other part of the network to indicate the response. Now any one interchanges the positions of ammeter and voltage source that means he or she connects the voltage source at the part of the network where the ammeter was connected and connects ammeter to that part of the network where the voltage source was connected. The response of the ammet

Read more »

Tellegen theorem

This theorem has been introduced in the year of 1952 by Dutch Electrical Engineer Bernard D.H. Tellegen. This is very useful theorem in network analysis. According to Tellegen theorem the summation of instantaneous powers for the n number of branches in an electrical network is zero. Are you confused ? Let’s explain. Suppose n number of branches in an electrical network have i1, i2, i3, ………….inrespective instantaneous currents through them. These currents satisfyKirchhoff current law. Again, suppose these branches have instantaneous voltages across them are v1, v2, v3, ……….. vn respectively. If these voltages across these elements sat

Read more »