A device for measuring the revolutions per minute (RPMs) of a revolving shaft, as with the drive shaft of an automobile or A device for measuring or indicating velocity or speed, as of blood, a river, a machine. It means that A tachometer measures how quickly something spins. Thus Standard tachometers measure revolutions of an object by attaching a sensor or using magnets to measure the speed of that object. Traditionally, tachometers are dials with a needle pointing to the current speed in RPMs (revolutions per minute). schematic of speed measurement of bike using microcontroller
What are digital Tachometers:
Digital tachometers use a pulse that senses the revolutions of the object, resulting in a number you see in a digital readout. Digital tachometers can also use optical sensors like a laser or reflective tape to measure rotations of an object.
Types of digital Tachometers:
Tachometers measure the angular speed of a rotating shaft. The speed of a shaft is measured in revolutions per minute (rpm). A tachometer could be as simple as a DC or AC generator that can determine the speed of shaft rotation by the amount of voltage the generator produces or the frequency of the output signal. The magnitude of the generator voltage and the frequency of the generated voltage will increase proportionally with speed. Frequency can also be measured by a photocell tachometer. The number of pulses produced by the photocell will increase as the speed of the shaft rotation increases.
There are many types of Tachometers depending upon the use , purpose , location and application of some particular tachometers.
- Direct coupling Tachometers
- Indirect coupling Tachometers
- Check in line Tachometers
- Laser diode based Tachometers
- Wheel based Tachometers
- moving with object tachometers
- stationary rotation finding tachometers
- ultrasound based tachometers
The frequency-type tachometer counts pulses produced by a rotating field tachometer, toothed rotor tachometer, or photocell tachometer. These types of tachometers produce sine waves or pulses that can be counted. These types of tachometers need a more sophisticated digital circuit to complete the process of count, store, calculate, display, and reset to get a value displayed that represents rpm. The rotating field and the toothed rotor tachometers produce a waveform and the photocell uses a rotating disk that has a number of windows in it.
Generalized properties and characteristics of Tachometers:
Tachometers are used to determine the speed of a motor shaft for motor drives on conveyors, and to determine the speed of rotation of the screw shaft on a plastic injection molding machine. The speed of rotation of the screw on a plastic injection molding machine is important to control because the screw shaft is used to meter the amount of plastic that is drawn into the barrel of the machine for the next injection shot. If the speed is not controlled, the screw will turn at different speeds and more or less plastic will be drawn into the barrel and the amount of plastic being used for each part will be inconsistent.
The properties of Tachometers involves following objects:
- Range (Typical commercial based tachometer may have 2.5 RPM to 99,999 RPM)
- Often based on reflection type sensing
- Features may have, minimum and maximum and average values during scanning of RPM
- Accuracy, may be around 0.05% of scale
- Update time or response time of overall system may be less than 0.9 Sec
- Memory: This is important feature of red by some supplier that the Tachometer can have storage facility of upto 255 reading and FIFO based optional.
- Laser Tachometer with remote sensors
- Optical RED LED based Tachometers, the operation of angle is important in this case. The critical angle may be in the range of -30 degree to +30 degree.
- In optical LED based Tachometer distance from the plate and sensor is also important.
- Some tachometer may use the visible light for sensing of object, again check the distance.
- Screw or wheel in contact Tachometers, the diameter and wearing and tearing is main parameter.
- At the resolution is primary parameter in selection of Tachometers.
The disk is connected to the tachometer shaft, so when it turns the windows line up with the photocell and the photocell produces a pulse when it is struck by light.
In each of these types of tachometers a pulse stream is produced and it is proportional to the speed of the tachometer shaft.
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