Reciprocating Saw - Variable Resistors and Switches By: Ryan Kim

Contents I.Introduction to the Saw and Variable Resistors II.Different Types of Variable Resistors III.Rheostats IV.Potentiometers V.Applications VI.Conclusion and References

Introduction Reference:

Introduction (Cont’d) Variable Switch Component Variable Resistors Resistance can change by turning a shaft or sliding a control Resistance tracks can be made of carbon, cermet, or a coil of wire Two main methods are to increase tension in the wire or to increase contact area Two main types are rheostats and potentiometers References:

Introduction (Cont’d) Schematic for Variable Resistors Overall Objective To learn how a variable resistor works To be able to distinguish the difference between a rheostat and a potentiometer To know the main applications for a variable resistor References:

Two Types of Variable Resistors Potentiometer (Rotary) 3 terminals (2 fixed, 1 variable) Normally used to vary voltage Most commonly used variable resistor 1 terminal at each end is hooked to power source 1 terminal in the middle acts as a wiper that axially rotates Turning a knob moves the wiper across a resistive metal strip (Modern resistors use a resistive plastic track) Rheostat (Linear Potentiometer) 2 terminals (1 fixed, 1 variable) Normally used to vary current Variable wiper end can be controlled by a slider or a screw mechanism for a rotating motion) Consists of a resistive track that is made of plastic (or metal) and the slider moves across the track, increasing or decreasing resistance References:

Rheostats (Linear Potentiometers) Often used with high currents Usually use a plastic track due to easy corrosion and wear from metal tracks Track orientation is linear (a.k.a. sliders) Track resistance can be either linear or logarithmic Reciprocating Saw Wiper moves along the track and decreases the resistance, which in turn, gives more voltage to the DC motor References:

Potentiometers (Rotary) Associated with lower current ratings Wiper rotates around a resistive metal strip to vary resistance from 0 to the maximum resistance Track orientation is rotational Usually used for fine-tuning a circuit (digital displays can be added to show number or rotations of dial) References:

Applications Potentiometer (Rotary) Volume controls Audio amplifiers Any other dial-based design Rheostat (Linear Potentiometer) Light dimmer switches (digital versions are now used) Variable speed switches (i.e. reciprocating saw) Faders and sliders on a mixer References: Figure 1 – Technics SH-MZ1200 Mixer

Conclusion and References Conclusion Several different types of variable resistors allow them to be used more widely in applications Linear variable resistor in a switch allows reciprocating saw to have a variable speed switch References 1)AAGE. “Technics SH-MZ1200.” Accessed on November 13, em/vare.asp?varenr= )“Potentiometer as a Voltage Divider.” Accessed on November 13, )Hewes, J. “Variable Resistors.” Accessed on November 13, )“Resistor.” Accessed on November 13,