24-09-2013, 03:11 PM
DESIGN AND CONSTRUCTION OF NON CONTACT DIGITAL TACHOMETER
[attachment=58271]
ABSTRACT
Tachometers are particularly suitable for the precision measurement and monitoring of time
related quantities by a magnetic wheel fixed to the shaft, or a high resolution pick up which can
be coupled directly to the motor shaft. In modern technological era, Engineers have designed
tachometers that could be used to measure the speed of shaft of the machinery without any
contact with the shaft. This is also referred to as non contact digital tachometer. This project was
aimed at analyzing the current prototype which uses a microcontroller Atmel AT82S59 for
measuring the rotation of a shaft. The heart of this tachometer is an IR sensor, also called opto
couple, which is a diode and photo diode. This opto-couple sends IR beam on the shaft to detect
its rotation. For that purpose, a small reflective sticker is added on the shaft, so that each rotation
of the shaft causes a "pulse" of IR light to be reflected.
Many problems were realized in its application, thus limiting the functionality of its usage. Some
of these problems were the sensor being used to produce a variable small signal for the reflection
of infra red light from the LED into the detector and to measure revolution per minute values less
than 60 rpm with a single pulse was problematic. The 8051 microcontrollers’ strength is
attributed to their simplicity and ease of use, but not in their processing power or diversity of
peripheral. When it is clocked at 8 MHz, it would give a throughput of only 666 KHz, because
8051 requires 12 clock cycles per instruction. An advanced microcontroller AVR ATmega 48
was used to replace the AT82S59 to deal with the problems. The sensor that was used is the
TCND-5000 FROM VISHAY SEMICONDUCTOR due to the package taking care of the optical
isolation between the sender and the receiver. Simple and effective IDE (integrated development
environment) was used for the programming. AVR Studio version 4.12 and the open source
WINAVR compiler for this purpose was used for the project. AVRISP mkII is connected to both
the PC and the target board for direct programming of the controller.
Background
A tachometer is an instrument used to measure the rotation speed of a shaft or disk, as with
electric motors. The device usually displays the revolutions per minute (RPM) on a calibrated
analogue dial, but digital displays are increasingly common. The term comes from Greek word
Ταχος, tachos, "speed", and metron, "to measure. The first mechanical tachometers were based
on measuring the centrifugal force, similar to the operation of a centrifugal governor. The
inventor was a German Engineer Dietrich Uhlhorn, who used it to measure the speed of
machines in 1817.
Tachometers as used on automobiles, aircraft, and other vehicles show the rate of rotation of the
engine's crankshaft, and typically have markings that indicate a safe range of operating speeds.
This can assist the driver in selecting appropriate throttle and gear settings for the perverting
driving conditions. Prolonged use at high speeds may cause inadequate lubrication, overheating
(exceeding capability of the cooling system), exceeding speed capability of sub-parts of the
engine (for example spring retracted valves) thus causing excessive wear or permanent damage
or failure of engines. This is much applicable to manual transmissions than to automatic types.
On analogue tachometers, speeds above maximum safe operating range are typically indicated
by a section of the gauge indicated in red, giving rise to the expression of "redlining" an engine
revolution of the engine up to the maximum safe limit. The red zone is superfluous on most
modern cars, since their engines typically have a revolution limiter which electronically limits
engine speed to prevent damage.
Significance of Study
This system is capable of accurate determination of shaft velocity, based on the outputs of an
incremental encoder. Previous error analyses of such devices which consider the nature of
counter operation are shown to be spacious. It is anticipated that sensor's non idealities, that is
producing a very small signal used to reflect infra red light from the LED into the detector and
the distance from the material is eliminated by directly connecting the sensor output to the
microcontroller and the controller is programmed to take care of the signal conditioning. An
estimate is made of the actual RPM output error, based on using multiple pulses per revolution
integrating the periods over time by Pulse Width Modulation within the microcontroller. Both
simulation and experimental results will be presented to confirm the utility of the enhanced
digital tachometer.
The sensor circuit
The heart of this tachometer is an IR sensor, also called opto couple, which is a diode and
photo diode in one package. This opto-couple will send IR beam on the shaft to detect its
rotation. For that purpose, a small reflective sticker is added on the shaft, so that each
rotation of the shaft will cause a "pulse" of IR light to be reflected. The sensor that will
be used is the TCND-5000 from VISHAY SEMICONDUCTOR, the decision to use this
one are a number factors, the most relevant being:
1. The packaging takes care of the optical isolation between the sender and the receiver.
2. The Emitter LED can sustain relatively high currents, and thus, can allow detection of
rotating shafts at bigger ranges.
XTAL1/XTAL2/TOSC1/TOSC2
Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port B output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port B pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port B pins are tri-stated when a reset condition becomes active, even
if the clock is not running.Depending on the clock selection fuse settings, PB6 can be used as
input to the inverting Oscillator amplifier and input to the internal clock operating circuit.
Depending on the clock selection fuse settings, PB7 can be used as output from the inverting
Oscillator amplifier.If the Internal Calibrated RC Oscillator is used as chip clock source, PB7..6
is used as TOSC2..1 input for the Asynchronous Timer/Counter2 if the AS2 bit in ASSR is set.
Overview
The ATmega48 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced
RISC architecture. By executing powerful instructions in a single clock cycle, the
ATmega48 achieves throughputs approaching 1MIPS per MHz allowing the system
designer to optimize power consumption versus processing speed.
Bit Copy Storage
The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or desti-
nation for the operated bit. A bit from a register in the Register File can be copied into T by the
BST instruction, and a bit in T can be copied into a bit in a register in the Register File by the
BLD instruction.
[attachment=58271]
ABSTRACT
Tachometers are particularly suitable for the precision measurement and monitoring of time
related quantities by a magnetic wheel fixed to the shaft, or a high resolution pick up which can
be coupled directly to the motor shaft. In modern technological era, Engineers have designed
tachometers that could be used to measure the speed of shaft of the machinery without any
contact with the shaft. This is also referred to as non contact digital tachometer. This project was
aimed at analyzing the current prototype which uses a microcontroller Atmel AT82S59 for
measuring the rotation of a shaft. The heart of this tachometer is an IR sensor, also called opto
couple, which is a diode and photo diode. This opto-couple sends IR beam on the shaft to detect
its rotation. For that purpose, a small reflective sticker is added on the shaft, so that each rotation
of the shaft causes a "pulse" of IR light to be reflected.
Many problems were realized in its application, thus limiting the functionality of its usage. Some
of these problems were the sensor being used to produce a variable small signal for the reflection
of infra red light from the LED into the detector and to measure revolution per minute values less
than 60 rpm with a single pulse was problematic. The 8051 microcontrollers’ strength is
attributed to their simplicity and ease of use, but not in their processing power or diversity of
peripheral. When it is clocked at 8 MHz, it would give a throughput of only 666 KHz, because
8051 requires 12 clock cycles per instruction. An advanced microcontroller AVR ATmega 48
was used to replace the AT82S59 to deal with the problems. The sensor that was used is the
TCND-5000 FROM VISHAY SEMICONDUCTOR due to the package taking care of the optical
isolation between the sender and the receiver. Simple and effective IDE (integrated development
environment) was used for the programming. AVR Studio version 4.12 and the open source
WINAVR compiler for this purpose was used for the project. AVRISP mkII is connected to both
the PC and the target board for direct programming of the controller.
Background
A tachometer is an instrument used to measure the rotation speed of a shaft or disk, as with
electric motors. The device usually displays the revolutions per minute (RPM) on a calibrated
analogue dial, but digital displays are increasingly common. The term comes from Greek word
Ταχος, tachos, "speed", and metron, "to measure. The first mechanical tachometers were based
on measuring the centrifugal force, similar to the operation of a centrifugal governor. The
inventor was a German Engineer Dietrich Uhlhorn, who used it to measure the speed of
machines in 1817.
Tachometers as used on automobiles, aircraft, and other vehicles show the rate of rotation of the
engine's crankshaft, and typically have markings that indicate a safe range of operating speeds.
This can assist the driver in selecting appropriate throttle and gear settings for the perverting
driving conditions. Prolonged use at high speeds may cause inadequate lubrication, overheating
(exceeding capability of the cooling system), exceeding speed capability of sub-parts of the
engine (for example spring retracted valves) thus causing excessive wear or permanent damage
or failure of engines. This is much applicable to manual transmissions than to automatic types.
On analogue tachometers, speeds above maximum safe operating range are typically indicated
by a section of the gauge indicated in red, giving rise to the expression of "redlining" an engine
revolution of the engine up to the maximum safe limit. The red zone is superfluous on most
modern cars, since their engines typically have a revolution limiter which electronically limits
engine speed to prevent damage.
Significance of Study
This system is capable of accurate determination of shaft velocity, based on the outputs of an
incremental encoder. Previous error analyses of such devices which consider the nature of
counter operation are shown to be spacious. It is anticipated that sensor's non idealities, that is
producing a very small signal used to reflect infra red light from the LED into the detector and
the distance from the material is eliminated by directly connecting the sensor output to the
microcontroller and the controller is programmed to take care of the signal conditioning. An
estimate is made of the actual RPM output error, based on using multiple pulses per revolution
integrating the periods over time by Pulse Width Modulation within the microcontroller. Both
simulation and experimental results will be presented to confirm the utility of the enhanced
digital tachometer.
The sensor circuit
The heart of this tachometer is an IR sensor, also called opto couple, which is a diode and
photo diode in one package. This opto-couple will send IR beam on the shaft to detect its
rotation. For that purpose, a small reflective sticker is added on the shaft, so that each
rotation of the shaft will cause a "pulse" of IR light to be reflected. The sensor that will
be used is the TCND-5000 from VISHAY SEMICONDUCTOR, the decision to use this
one are a number factors, the most relevant being:
1. The packaging takes care of the optical isolation between the sender and the receiver.
2. The Emitter LED can sustain relatively high currents, and thus, can allow detection of
rotating shafts at bigger ranges.
XTAL1/XTAL2/TOSC1/TOSC2
Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port B output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port B pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port B pins are tri-stated when a reset condition becomes active, even
if the clock is not running.Depending on the clock selection fuse settings, PB6 can be used as
input to the inverting Oscillator amplifier and input to the internal clock operating circuit.
Depending on the clock selection fuse settings, PB7 can be used as output from the inverting
Oscillator amplifier.If the Internal Calibrated RC Oscillator is used as chip clock source, PB7..6
is used as TOSC2..1 input for the Asynchronous Timer/Counter2 if the AS2 bit in ASSR is set.
Overview
The ATmega48 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced
RISC architecture. By executing powerful instructions in a single clock cycle, the
ATmega48 achieves throughputs approaching 1MIPS per MHz allowing the system
designer to optimize power consumption versus processing speed.
Bit Copy Storage
The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or desti-
nation for the operated bit. A bit from a register in the Register File can be copied into T by the
BST instruction, and a bit in T can be copied into a bit in a register in the Register File by the
BLD instruction.