Optical sensors and optical Tachometers:
As we know that almost all tachometers in any term use a sensor to complete their operation. Digital tachometers with optical sensors are often known as optical tachometers. Optical pulses can be generated by one of the two alternatives photoelectric tachniques illustrated in Figure, the pulses are produced as the windows or gap in dicks in a slotted disc pass in sequence between a light source and a detector (photo-diode or LDR or photo-transistor). The alternative form has both light source and detector mounted on the same side of a reflective disc which has black sectors painted onto it at regular angular intervals. Light sources
are normally either lasers or LEDs, with photodiodes and phototransistors being used as detectors.
So the optical sensor for optical tachometer in this case would be consist of following parts in general:
1. LED (light source)
2. LDR , photo-diode (light detector)
3. obstacle dice ( having some gaps and close intervals)
There are certain advantages and dis-advantages of the optical sensors. Optical tachometers yield better accuracy than other forms of digital tachometer but are not as reliable because dust and dirt can block light paths.
Inductive sensors for Tachometers:
Variable reluctance velocity transducers, also known as induction tachometers, are a form of digital tachometer that uses inductive sensing. They are widely used in automotive industry within anti-skid devices, anti-lock braking systems (ABS) and traction control. A more sophisticated version shown in Figure. It has a rotating disc that is constructed from a bonded fiber material into which soft iron poles are inserted at regular intervals around its periphery. The sensor consists of a permanent magnet with a shaped pole piece, which carries a wound coil. The distance between the pick-up and the outer perimeter of the disc is around 0.5 mm. As the disc rotates, the soft iron inserts on the disc move in turn past the pick-up unit. As each iron insert moves towards the pole piece, the reluctance of the magnetic circuit increases and hence the flux in the pole piece also increases. Similarly, the flux in the pole piece decreases as each iron inserts moves away from the sensor. The changing magnetic flux inside the pick-up coil causes a voltage to be induced in the coil whose magnitude is proportional to the rate of change of flux.
This voltage is positive while the flux is increasing and negative while it is decreasing. Thus, the output is a sequence of positive and negative pulses whose frequency is proportional to the rotational velocity of the disc. The maximum angular velocity that the instrument can measure is limited to about 10000 rpm because of the finite width of the induced pulses. As the velocity increases, the distance between the pulses is reduced, and at a certain velocity, the pulses start to overlap. At this point, the pulse counter ceases to be able to distinguish the separate pulses.
The optical tachometer has significant advantages in this respect, since the pulse width is much narrower, allowing measurement of higher velocities.
A simpler and cheaper form of variable reluctance transducer also exists that uses a ferromagnetic gear wheel in place of a fiber disc. The motion of the tip of each gear tooth towards and away from the pick-up unit causes a similar variation in the flux pattern to that produced by the iron inserts in the fiber disc.
The pulses produced by these means are less sharp, however, and consequently the maximum angular velocity measurable is lower.
Output of the tachometer (magnetic pickup) is given by
E=bmwr sin (mwrt)
b- amplitude of flux variation
m- number of teeth in the rotating wheel
wr -angular velocity of the rotating wheel
Thus sinusoidal signal amplitude E= bmwr and frequency f=mwr/2π are proportional to angular velocity of wheel.
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As we know that almost all tachometers in any term use a sensor to complete their operation. Digital tachometers with optical sensors are often known as optical tachometers. Optical pulses can be generated by one of the two alternatives photoelectric tachniques illustrated in Figure, the pulses are produced as the windows or gap in dicks in a slotted disc pass in sequence between a light source and a detector (photo-diode or LDR or photo-transistor). The alternative form has both light source and detector mounted on the same side of a reflective disc which has black sectors painted onto it at regular angular intervals. Light sources
are normally either lasers or LEDs, with photodiodes and phototransistors being used as detectors.
So the optical sensor for optical tachometer in this case would be consist of following parts in general:
1. LED (light source)
2. LDR , photo-diode (light detector)
3. obstacle dice ( having some gaps and close intervals)
There are certain advantages and dis-advantages of the optical sensors. Optical tachometers yield better accuracy than other forms of digital tachometer but are not as reliable because dust and dirt can block light paths.
Inductive sensors for Tachometers:
Variable reluctance velocity transducers, also known as induction tachometers, are a form of digital tachometer that uses inductive sensing. They are widely used in automotive industry within anti-skid devices, anti-lock braking systems (ABS) and traction control. A more sophisticated version shown in Figure. It has a rotating disc that is constructed from a bonded fiber material into which soft iron poles are inserted at regular intervals around its periphery. The sensor consists of a permanent magnet with a shaped pole piece, which carries a wound coil. The distance between the pick-up and the outer perimeter of the disc is around 0.5 mm. As the disc rotates, the soft iron inserts on the disc move in turn past the pick-up unit. As each iron insert moves towards the pole piece, the reluctance of the magnetic circuit increases and hence the flux in the pole piece also increases. Similarly, the flux in the pole piece decreases as each iron inserts moves away from the sensor. The changing magnetic flux inside the pick-up coil causes a voltage to be induced in the coil whose magnitude is proportional to the rate of change of flux.
This voltage is positive while the flux is increasing and negative while it is decreasing. Thus, the output is a sequence of positive and negative pulses whose frequency is proportional to the rotational velocity of the disc. The maximum angular velocity that the instrument can measure is limited to about 10000 rpm because of the finite width of the induced pulses. As the velocity increases, the distance between the pulses is reduced, and at a certain velocity, the pulses start to overlap. At this point, the pulse counter ceases to be able to distinguish the separate pulses.
The optical tachometer has significant advantages in this respect, since the pulse width is much narrower, allowing measurement of higher velocities.
A simpler and cheaper form of variable reluctance transducer also exists that uses a ferromagnetic gear wheel in place of a fiber disc. The motion of the tip of each gear tooth towards and away from the pick-up unit causes a similar variation in the flux pattern to that produced by the iron inserts in the fiber disc.
Output of the tachometer (magnetic pickup) is given by
E=bmwr sin (mwrt)
b- amplitude of flux variation
m- number of teeth in the rotating wheel
wr -angular velocity of the rotating wheel
Thus sinusoidal signal amplitude E= bmwr and frequency f=mwr/2π are proportional to angular velocity of wheel.
TAGS:-8051 Project, 8051 projects,ADC0804,adc0808,adc0809,microcontroller projects, at89c51 projects, 8051 serial port communication,Proteus projects,atmega128pc,stepper motor,control of stepper motor, motion controller, motion detection, motion detector,clockwise motion, anti clockwise motion, direction of motion detection circuit diagram, 74ls74 for motion detection, sensor for motion detection,how to find direction of motion,car tachometer,tachometer circuit,tachymeter,tachometer watch,digital tachometer,odometer,optical tachometer,speedometer,Aircraft Tachometer ,aircraft Tachometers ,Cessna Tachometers ,Cessna, Diamond, Mooney, Piper, Mitchell Aircraft Tachometers ,Avionics,Airpax Speed Sensors, online buy Speed sensor, hall effect sensors, passive sensors, magnetic Speed Sensor, Bi-Directional, Dual Channel,industrial tachometer sensor to measure the angular speed of rotating machinery,Brushless RPM sensor,Tachometer Sensor Manufacturer and Supplier,Remote Optical Sensor for Tachometer,Magnetic tachometer Sensor with Amplifier Module. Magnetic Sensor with Amplifier Module,photodetectors, transmissive and reflective opto-sensors,"Reflective Optical Sensor" and "Optocoupler" are two very different things,diode-transistor optocouplers,Optical Sensors CCDs, MEMS, CMOS, photodiodes, optocouplers emulator notes in microcontroller 8051
Hy ,
ReplyDeletesorry for sending this email again but i've just noticed that I forgot to write something as Subject.
I would really appreciate it if you could help me with a project I'm trying to do . I've started working on my bachelor project but a software-only approach doesn't fulfill the requirements so , without prior experience , i've started reading about mcu's sensors and rf Transceiver modules ; the device I'm trying to build should collect data from a few sensors and send them to a pc throw a 802.11b Transceiver ; something like MotionBee : but with a power regulator , or what i would need for it to work on batteries (maybe i could use a 3.7v 1.2A nokia battery) with a 802.11b transceiver and optionally an OLED display . could you maybe recommend me a board with a mcu to which i could connect the sensors and the rf transceiver ? and any suggestion, maybe books/documentation that i could read on this subject would be welcomed.
Thank you ,
Emanuel
i need to read the feedback from a2 channel servo motor that has an optical sensor as techometer... how should i start 8051 programming?
ReplyDelete@ USMANIUM (8051 programming and servo motor 02 channel control):-
ReplyDelete1. for feedback cntrol, you need input against that you will hav output to control, so study your system, and try to find out which input is available like speed or position then fix sensor for it.
2. draw circuit diagram of your control system and then stage come for programming.
3. different compilers for 8051 are available on internet for programming, but you should select any compiler based on your expertise on language. like assembly or c or Fortron or basic