Active and Passive Components

SEE710 INSTRUMENTATION AND PROCESS CONTROL
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QUESTION ONE
Q1. The Main Difference between Active and Passive Components
Active components or devices that need external source to their operation, for example
transistor, diode and SCR. Taking example of diode for explanation. When diode is connected in
an electric circuit and then that circuit is connected to the voltage supply then the diode will
conduct current till the voltage supplied reaches 0.7 ( for silicon) and 0.3 ( for germanium).
Passive components or devices are those which do not need any external source for them to
operate. For example, capacitor, resistor and inductor. Taking resistor as example for
explanation. Unlike diode, resistors do not need 0.7 or 0.3. When resistor is connected to voltage
supply, it will start operating automatically as anticipated without any specific voltage.
QUESTION TWO
Null Type method
This is a type of instrument which tries to maintain a deflection at zero through appropriate
application of known impact opposing the produced deflection through measured quality. The
measured quantity generates some mechanical impacts which engenders equal but having a
reverse effect in the instrument part.
Advantages Null Type method of instrument
Such instruments are highly accurate
Null type instruments are readily used for measuring
Disadvantages of using null type instrument

Because of addition dissimilar weights used this type of instrument is difficult.
Deflection type method
 These are instruments where pointer system is employed to illustrate the output of the
system. The accuracy of this instrument is dependent on the calibration linearity of the
spring.
Advantages of deflection type of instrument
 In this type of instrument it is very easy read the results of deflection.
 Because of convenient use of these instruments, they are readily used for calibrations.
Disadvantages of deflection instruments
These instruments have less accuracy.
Some types of null instruments used include the following;
i. Wheatstone bridge
This is a null type electrical instrument which is employed for measuring an unknown resistance
in electrical circuit via balancing 2 legs of bridge circuit where one of the legs contains
unknown. Wheatstone bridge is illustrated using the following diagram;

Figure 1: Showing Wheatstone bridge
ii. Potentiometer
This is an instrument where a slide wire is calibrated in emf, the calibration is done through the
use of emf standard source. This type of instrument is employed for measuring the electro
motive force of particular cell. This instrument also aids in comparing the electro motive force
for different cells. The instrument can also be employed in varying the resistor in several
application like a volume knob of radio receiver. This instrument can be illustrated using the
following diagram;
Figure 2: showing potentiometer