Reactance and Impedance

Impedance

Impedance, Z =  V  I

Resistance, R =  V  I

V = voltage in volts (V) I  = current in amps (A) Z = impedance in ohms () R = resistance in ohms ()

Impedance (symbol Z) is a measure of the overall opposition of a circuit to current, in other words: how much the circuit impedes the flow of current. It is like resistance, but it also takes into account the effects of capacitance and inductance. Impedance is measured in ohms, symbol . Impedance is more complex than resistance because the effects of capacitance and inductance vary with the frequency of the current passing through the circuit and this means impedance varies with frequency! The effect of resistance is constant regardless of frequency.
The term 'impedance' is often used (quite correctly) for simple circuits which have no capacitance or inductance - for example to refer to their 'Input Impedance' or 'output impedance'. This can seem confusing if you are learning electronics, but for these simple circuits you can assume that it is just another word for resistance.
Four electrical quantities determine the impedance (Z) of a circuit:
resistance (R), capacitance (C), inductance (L) and  frequency (f).
Impedance can be split into two parts:

• Resistance R (the part which is constant regardless of frequency)
• Reactance X (the part which varies with frequency due to capacitance and inductance)

Matching for Impedance

How important is impedance matching?

It can be shown mathematically that any source of power e.g. a receiver antenna, an audio amplifier or an amateur radio transmitter will deliver its maximum possible power output when the impedance of the subsequent load is equal to the internal impedance of that source. This is achieved through impedance matching.
Unfortunately in this situation the efficiency can only be 50% because half the power is consumed in the source.

Examples of Impedance Matching

Our first example is one of an old type transistor radio where in the audio stages the output speaker was a typical 8 ohms. Such stages are impedance matched by audio transformers as depicted in figure 1 below.

Fig 1 - schematic of impedance matching of transistor audio stages

Transformer for Audio

Audio transformers are "wide band" transformers. In essence a "transformer" is two or more windings coupled by a common magnetic field. It is this magnetic field which provides the means to pass voltages and currents from the primary winding to the secondary winding when alternating current flows.
Essentially the main purpose of an interstage audio transformer is to isolate the DC and couple the signal, with minimal loss. The transformer windings look like short circuits to DC, yet are seen as complex impedances to the AC signal.
Much which follows on the topic of audio transformers is of necessity somewhat over simplified to give a general overview. A transformer schematic is depicted in Figure 1 below.

Figure 1. - audio transformers schematic 

Inductance

What is inductance?

The property of inductance might be described as "when any piece of wire is wound into a coil form it forms an inductance which is the property of opposing any change in current". Alternatively it could be said "inductance is the property of a circuit by which energy is stored in the form of an electromagnetic field".
We said a piece of wire wound into a coil form has the ability to produce a counter emf (opposing current flow) and therefore has a value of inductance. The standard value of inductance is the Henry, a large value which like the Farad for capacitance is rarely encountered in electronics today. Typical values of units encountered are milli-henries mH, one thousandth of a henry or the micro-henry uH, one millionth of a henry.
A small straight piece of wire exhibits inductance (probably a fraction of a uH) although not of any major significance until we reach UHF frequencies.
The value of an inductance varies in proportion to the number of turns squared. If a coil was of one turn its value might be one unit. Having two turns the value would be four units while three turns would produce nine units although the length of the coil also enters into the equation.

 

Basic Capacitance

What is capacitance?

In the topic current  we learnt of the unit of measuring electrical quantity or charge was a coulomb. Now a capacitor (formerly condenser) has the ability to hold a charge of electrons.
The number of electrons it can hold under a given electrical pressure (voltage) is called its capacitance or capacity. Two metallic plates separated by a non-conducting sunstance between them make a simple capacitor. Here is the symbol of a capacitor in a pretty basic circuit charged by a battery.

Figure 1. - capacitor schematic in a circuit

Resistor

Example:      
                                         



Circuit symbol:   

 

Function

Resistors restrict the flow of electric current, for example a resistor is placed in series with a light-emitting diode (LED) to limit the current passing through the LED.

Connecting and soldering

Resistors may be connected either way round. They are not damaged by heat when soldering.

Some Solved Examples

Example 1) Temperature measurement before a chemical reactor:
The feed temperature, T₃, to an isothermal chemical reactor should be controlled very accurately in the range of 400K.  The product quality is measured only once every shift by laboratory analysis.  The operator adjusts the set point of the feed temperature controller to achieve the desired product quality.  What temperature sensor do you recommend?

Why to Design Fail-Safe

Logic circuits, whether comprised of electromechanical relays or solid-state gates, can be built in many different ways to perform the same functions. There is usually no one "correct" way to design a complex logic circuit, but there are usually ways that are better than others.
In control systems, safety is (or at least should be) an important design priority. If there are multiple ways in which a digital control circuit can be designed to perform a task, and one of those ways happens to hold certain advantages in safety over the others, then that design is the better one to choose.
Let's take a look at a simple system and consider how it might be implemented in relay logic. Suppose that a large laboratory or industrial building is to be equipped with a fire alarm system, activated by any one of several latching switches installed throughout the facility. The system should work so that the alarm siren will energize if any one of the switches is actuated. At first glance it seems as though the relay logic should be incredibly simple: just use normally-open switch contacts and connect them all in parallel with each other:

Interlock and Permissive circuits

A practical application of switch and relay logic is in control systems where several process conditions have to be met before a piece of equipment is allowed to start. A good example of this is burner control for large combustion furnaces. In order for the burners in a large furnace to be started safely, the control system requests "permission" from several process switches, including high and low fuel pressure, air fan flow check, exhaust stack damper position, access door position, etc. Each process condition is called a permissive, and each permissive switch contact is wired in series, so that if any one of them detects an unsafe condition, the circuit will be opened:

Flowmeter Orifice With Turn Down Ratio

Orifice, combined with differential pressure transmitter, is the mostly used flow measurement device in oil & gas plant because of low cost and its ease of installation and maintenance. However, orifice only allows 3:1 rangeability to maintain accuracy. This means, if one wants to measure maximum flow of 10 MMscfd, then the minimum flow measurement that could be measured is only 3.3 MMscfd.

According to Bernoulli principle, the relationship between flow and pressure drop of fluid passing through an orifice is given by the following formulae:

DP Level Calibration (Diaphragm Seal) with Capillary

H = 100 Inch (Center to Center)
SG Process Liquid = 1
h = 50 Inch
Fill fluid SG = 2.1
What is the calibrated range? what is the required URV and LRV of DP transmitter for cases below:
1. The first case (atmospheric) are as follows: 

Calibration of Control Valve

Control Valve is the terminology used to a throttling valve which has the ability, or the gradual changing. Is on-off valve including valve controlled? Yes, but rarely referred to as the control valve. Particularly in view of the control valve to valve that can receive both analog command with a collection of analog signals and digital signals.

Evolution Instrument and Control System

History is a great art, a great benefit for live human lesson learned; Ibnu Khaldun told us. The history is not only important for discussing about past war, kings step-up and step-down, occupations, politics and religions. History should tell us how was technology discovered? how was technology’s evolution process, how could technology save people and get better life?, how was it made?. If Charles Darwin said “The Origin of Species; by Means of Natural Selection” then we could say “The Origin of Instrumentation and Control; by Means of Technological Selection”. By these words, the Instrumentation and Control Evolution term has been proudly presented.

Komodo can be classified as an ancient reptile that can stand up to natural selection. There is no harm in also called Bourdon gauge and pneumatic systems that still exist in modern industry as an ancient instrument that can withstand the technology selection. They survive because of their reliability, robustness, safety, and yet there is no substitute. Evolution of Instrumentation and control began in the 1930s until the 2000s, this collection of articles disclosed in the Maintenance of Instrumentation and Control (editor: Lawrence D. Goettsche).

Anti Surge Control System

Centrifugal compressor has three operating parameters are: Speed, Head, and Flow. Speed is the rotational speed compressor, the Head is the energy or force or capacity compressor (units feet or meters of unit length, so confused: p) to raise the pressure of the inlet pressure (Pin) to the outlet pressure (Pout), Flow is the flow of fluid being transferred by the compressor. "Centrifugal compressor can reach the maximum condition headnya at a certain speed, these conditions will be passed on the fluid flow is also certain." The above statement is called the boundary conditions peak of the compressor stable. Well, when Headnya rising (meaning larger Pout) then the flowrate to be dropped following the Performance Curve of the compressor. Pout increases could be due to the discharge pipe that is streamed by the compressor there is blockage, the filter is dirty, no clothes left in the pipe (ahh this is not possible), etc.. Sample Performance Curve of the compressor as follows: 

Pressure Calibration

Calibration of Pressure / Pressure is an activity undertaken to ensure that the zero, span, accuracy and linearity of a pressure instrument according to the actual pressure value (standard). Accuracy was determined by comparing instrument readings with the test pressure gauge reading standards for some points that can be done by random. Linearity is determined by giving increasing in and Decreasing pressure and see the response of the pressure instrument is whether to form a linear equation or a curve equation / polynomial. If not linear then the adjustment should be made. Zero is the value of pressure on the state of zero pressure (1 atmosphere). Span is the difference between the maximum value to minimum value. While the range is the minimum value to maximum.

One PhaseTransformer and Three Phase Transformer

Up to this point in the manual, we have focused primarily upon single-phase transformers. Single-phase meaning (2) power lines as an input source; therefore, only (1) primary and (1)secondary winding is required to accomplish the voltage transformation. However, most power is distributed in the form of three-phase A.C. Therefore, before proceeding any further you should understand what is meant by three-phase power. Basically, the power company generators produce electricity by rotating (3) coils or windings through a magnetic field within the generator . These coils or windings are spaced120 degrees apart. As they rotate through the magnetic field they generate power which is then sent out on three (3) lines as in three-phase power. Three-Phase transformers must have (3) coils or windings connected in the proper sequence in order to match the incoming power and therefore transform the power company voltage to the level of voltage we need and maintain the proper phasing or polarity. Three phase electricity powers large industrial loads more efficiently than single-phase electricity. When single-phase electricity is needed, It is available between any two phases of a three-phase system, or in some systems , between one of the phases and ground. By the use of three conductors a three-phase system can provide 173% more power than the two conductors of a single-phase system. Three-phase power allows heavy duty industrial equipment to operate more smoothly and efficiently. Three-phase power can be transmitted over long distances with smaller conductor size. In a three-phase transformer, there is a three-legged iron core as shown below. Each leg has a respective primary and secondary

UPS (Uninterruptable Power Supply)

Even a brief power outage could result in loss of unsaved data on a computer that was running. An

uninterruptible power supply (UPS)

is an electronic device that continues to supply electricity to the load for a certain period of time during a utility failure or when the line voltage varies outside the normal limits. Its typical application is PC backup power. Large models can be used to feed an entire home, servers or other equipment.

Power Supply

Electricity from the grid is transmitted in the form of poorly regulated AC, while electronic circuits normally require a stabilized DC. A

power supply
unit (PSU) is a device that transfers electric energy from a source to a load and in the process changes its characteristics to meet specific requirements. A typical application of power supplies is to convert a utility's AC voltage into regulated DC voltage(s) required for an electronics and to provide safety isolation from the mains. Depending on the mode of operation of power semiconductors, PSU can be linear or switching (SMPS).

Power Electrical

The EPS consists of three subsystems: power reactant storage and distribution, fuel cell power plants (electrical power generation) and electrical power distribution and control.
The PRSD subsystem stores the reactants (cryogenic hydrogen and oxygen) and supplies them to the three fuel cell power plants, which generate all the electrical power for the vehicle during all mission phases. In addition, cryogenic oxygen is supplied to the environmental control and life support system for crew cabin pressurization. The hydrogen and oxygen are stored in their respective storage tanks at cryogenic temperatures and supercritical pressures. The storage temperature of liquid oxygen is minus 285 F and minus 420 F for liquid hydrogen.

Bias of Transistor

Bipolar transistor amplifiers must be properly biased to operate correctly. In circuits made with individual devices (discrete circuits), biasing networks consisting of resistors are commonly employed. Much more elaborate biasing arrangements are used in integrated circuits, for example, bandgap voltage references and current mirrors.
The operating point of a device, also known as bias point, quiescent point, or Q-point, is the point on the output characteristics that shows the DC collector–emitter voltage (V_ce) and the collector current (I_c) with no input signal applied. The term is normally used in connection with devices such as transistors.