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...