ENGINEERING ARTICLES

I) PRIMARY SENSING ELEMENT This is the element that first receives energy from the measured medium and procedures an output depending on some way on the measured quantity (measured).  The output is some physical variable e.g. displacement or voltage. An instrument always extract some energy from the measured medium. The measured quantity is always disturbed by the act of measurement, which makes a perfect theoretically impossible. Good instruments are designed to minimize this loading effect.  II) VARIABLE CONVERSION ELEMENT If may be necessary to convert the output signal of the primary sensing element to another more suitable variable while preserving the information content of the original signal. This element performs this function.  III) VARIABLE MANIPULATION ELEMENT An instrument may require that a signal represented by some physical variable be manipulated by some way.  By manipulation we mean specifically a change in numerical ...

Resistive Load Resistive loads can be purely resistive or of the tungsten-heater load type. A resistive load that has no heating element is the easiest for a switch to handle, and the switch’s rating is based on this type of load. A resistive load is one in which 100% of the load is composed of resistive devices. The power factor is high (PF = 1) and contact erosion is low. Consequently, the switch’s electrical life can be anticipated with some certainty.  Lamp Load When a switch closes on a resistive lamp load, the switch sees a short circuit because the cold resistance of the lamp filament is near zero. The surge current as the switch closes can be many times the steady state current. As the lamp filament heats up to operating temperature, the resistance of the filament increases and the current decreases to the lamp’s steady state.  Motor Motor loads present yet another brutal environment for switch contacts. Closing the switch contact on a motor st...

A structural design project may be divided into three phases, i.e. planning, design and construction.  Planning: This phase involves consideration of the various requirements and factors affecting the general layout and dimensions of the structure and results in the choice of one or perhaps several alternative types of structure, which offer the best general solution. The primary consideration is the function of the structure. Secondary considerations such as aesthetics, sociology, law, economics and the environment may also be taken into account. In addition there are structural and constructional requirements and limitations, which may affect the type of structure to be designed.  Design: This phase involves a detailed consideration of the alternative solutions defined in the planning phase and results in the determination of the most suitable proportions, dimensions and details of the structural elements and connections for constructing each alternative structural...

The Hipot Test (Dielectric Voltage Withstand) The Hipot test is the most common type of safety test. This test is designed to stress a product’s insulation beyond what it would encounter during normal use. The reasoning behind this test is that if the insulation can withstand high voltage for short period of time, it will be safe to use at nominal voltage throughout its useful life. One of the main advantages of the Hipot test is its versatility. In addition to measuring leakage currents and detecting breakdowns, you can also use it to detect:  Material and workmanship defects.  Weak points in the insulation.  Small gap spacing between conductors. Air is just an insulator and Hipot voltage will “jump” through the air across gaps that are too small.  Condensation, dirt and contaminants in the insulation. When running a Hipot test, high voltage is applied to the mains conductors (LINE and NEUTRAL). The Hipot return point is connected to the bare metal...

There are several types of the electronic circuitry used within battery chargers for the marine market. FERRO-RESONANT (or CVT) These use a low-frequency MAGNETIC control system, which makes them very HEAVY, very BULKY and is also only available with a poor FLOAT charge characteristic, therefore very SLOW recharging. They can also generate a large magnetic field which can upset other equipment on board. On the plus side, they are CHEAP and RELIABLE due to the low number of components used and they tend to appeal to boat-builders who put the price at the top of their list of priorities.  LINEAR CHARGERS These also use a low-frequency transformer to reduce the input voltage to a lower level but then use transistors to control the current and voltage fed to the battery. This technique can be used for either FLOAT or 3-STAGE chargers but is very IN-EFFICIENT and therefore HOT, HEAVY and BULKY. The biggest drawback is a LIMITED INPUT VOLTAGE range - not ideal for running from a...

The LC and RC oscillators have their own limitations. The major problem in such circuits is that their operating frequency does not remain strictly constant. There are two principal reasons for it viz.,  As the circuit operates, it will warm up. Consequently, the values of resistors and inductors, which are the frequency determining factors in these circuits, will change with temperature. This causes the change in frequency of the oscillator.  If any component in the feedback network is changed, it will shift the operating frequency of the oscillator.  However, in many applications, it is desirable and necessary to maintain the frequency constant with extreme low tolerances. For example, the frequency tolerance for a broadcasting station should not exceed 0.002% i.e. change in frequency due to any reason should not be more than 0.002% of the specified frequency. The broadcasting stations have frequencies which are quite close to each other. In fact, the fr...

An electronic device that generates sinusoidal oscillations of desired frequency is known as a sinusoidal oscillator. Oscillator does not create energy, but merely acts as an energy converter. It receives DC energy and changes it into AC energy of desired frequency. The frequency of oscillations depends upon the constants of the device. Although an alternator produces sinusoidal oscillations of 50Hz, it cannot be called an oscillator. Firstly, an alternator is a mechanical device having rotating parts whereas an oscillator is a non-rotating electronic device. Secondly, an alternator converts mechanical energy into AC energy while an oscillator converts DC energy into AC energy. Thirdly, an alternator cannot produce high frequency oscillations whereas an oscillator can produce oscillations ranging from a few Hz to several MHz.  Advantages Although oscillations can be produced by mechanical devices (e.g. alternators), but electronic oscillators have the following advantage...