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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: http://www.ryobitools.com
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: http://www.ryobitools.com
http://en.wikipedia.org/wiki/Resistor
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: http://www.allaboutcircuits.com/vol_6/chpt_3/6.html
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: http://www.allaboutcircuits.com/vol_6/chpt_3/6.html
http://www.kpsec.freeuk.com/components/vres.htm
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: http://www.allaboutcircuits.com/vol_6/chpt_3/6.html
http://www.kpsec.freeuk.com/components/vres.htm
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: http://www.allaboutcircuits.com/vol_6/chpt_3/6.html
http://www.kpsec.freeuk.com/components/vres.htm
Applications
Figure 1 – Technics SH-MZ1200 Mixer
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: http://en.wikipedia.org/wiki/Resistor
http://www.kpsec.freeuk.com/components/vres.htm
http://www.aage.dk/default.asp?page=/Shoppingsystem/vare.asp?varenr=26
398
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, 2005
http://www.aage.dk/default.asp?page=/Shoppingsyst
em/vare.asp?varenr=26398.
2) “Potentiometer as a Voltage Divider.” Accessed on
November 13, 2005
http://www.allaboutcircuits.com/vol_6/chpt_3/6.html.
3) Hewes, J. “Variable Resistors.” Accessed on
November 13, 2005
http://www.kpsec.freeuk.com/components/vres.htm.
4) “Resistor.” Accessed on November 13, 2005
http://en.wikipedia.org/wiki/Resistor.