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ME 361: Instrumentation and Measurement 

aminul islam khan

Electronics : Basics 

Basic Input Circuits

Most common input circuits used in transducerwork:

1. Current-sensitive Circuit

2. Voltage-sensitive (ballast) Circuit

3. Voltage-divider Circuit

4. Voltage-balancing Potentiometer Circuit

5. Bridge Circuit

6. Amplifier CircuitCurrent-sensitive Input Circuit

• Current flow through the circuit indicates sensor’s resistance R.

• Current flow varies linearly with R for some ranges of operation.

Voltage-sensitive (ballast) Circuit

• Voltmeter impedance is very high & draws negligible current.

• Change in R is indicated by voltage change.

• Sensitivity, S = dEo/dR

• For maximum sensitivity, dS/dRi = 0, gives R=Ri

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ME 361: Instrumentation and Measurement 

aminul islam khan

Electronics : Basics 

• Anode : +ve side of source where electrons are attracted.• Cathode : -ve side from where electrons are released.

• Ground : a reference point where voltage is assumed zero.

• Load : network of circuit elements that dissipate or store electrical energy.

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ME 361: Instrumentation and Measurement 

aminul islam khan

Electronics : Basics 

• Ground indicates a reference point in the

circuit where the voltage is assumed to be

zero.

• There are three basic passive elements: the

resistor (R), capacitor (C) and inductor (L).

• Passive elements require no additional

power supply, as active elements such as

integrated circuits.

• There are two types of ideal energy sources:

a voltage source (V) and a current source (I).• Ideal sources contain no internal resistance,

inductance or capacitance.

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ME 361: Instrumentation and Measurement 

aminul islam khan

Electronics : Basics 

Resistor

• Capacitance is a property of the dielectric material, the

plate geometry and separation.

• Capacitors block DC voltage and pass the AC voltage. DC

voltage will build a potential difference in the capacitor

until they are equal. AC voltage simply alternates the

charge and discharge of the capacitor and is passed, not

blocked, in a circuit.

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ME 361: Instrumentation and Measurement 

aminul islam khan

Electronics : Basics 

• Current through an inductor cannot change

instantaneously because it is an integral of the voltage.

Motor, electromagnetic relays or solenoids have large

inductance, so it is difficult to turn these ON or OFF very

fast.

• The inductor is made by a coil of conductor around a

core like a solenoid.

• What happens if you open a switch that is providing

current to an inductor?

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ME 361: Instrumentation and Measurement 

aminul islam khan

Electronics : Basics 

Ohm's Law: E = IR

Kirchhoff's Laws (V,I)

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ME 361: Instrumentation and Measurement 

aminul islam khan

Electronics : Basics 

KVL…..

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ME 361: Instrumentation and Measurement 

aminul islam khan

Electronics : Basics 

Voltage Divider…..

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ME 361: Instrumentation and Measurement 

aminul islam khan

Electronics : Basics 

Voltage Divider…..Example

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ME 361: Instrumentation and Measurement 

aminul islam khan

Electronics : Basics 

Diodes…..

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ME 361: Instrumentation and Measurement 

aminul islam khan

Electronics : Basics 

Diodes Homework…..

Diode: some important factors…

• Forward voltages of silicon diodes are really small ( ̴0.6-0.7 volts)

• Diodes don’t have resistance. If the voltage is below a diode’s forward voltage,

then the element looks like an open circuit. If the voltage is below the forward

voltage, the element behaves as a short circuit

Assignment……

Q. Write a short note on Zener Diodes

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ME 361: Instrumentation and Measurement 

aminul islam khan

Electronics : Basics 

Diodes Homework 2…..

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ME 361: Instrumentation and Measurement 

aminul islam khan

Electronics : Basics 

Relays…