1.1 Introduction
The infared sensor are widely used in industries for scanning bar-code and detecting material. The research in measuring position recently become more
important. The measurement of position for rotating and linearly translatings parts is a key requirement in automation. [1]. Before this, the tachometer is using to measure
rotating part. A tachometer is a device to measure speed of rotating shaft in the angular speed which mean in revolutions per minute. The tachometers are widely
used in industries to measure angular speed in generators and motor. There are lots of tachometer with different type of sensing technique but they have disadvantages.
Among disadvantages are montaging the sensor required time and lack of precision in measurement. There are many types of technique to use to sense the speed of
rotating shaft. For example: toothed-rotor tachometers and optical rotary encoder.
The toothed-rotor tachometers is used several ferromagnetic tooth on its rotor. Then, a permanent magnet with a coil wrapped around it, is placed in the
motor stator. The changing of magnetic field strength will induce a voltage. For every rotor tooth one voltage pulse is produced. The input voltage pulse will be
converted into frequency as an output signal. Figure 1.1 has shown toothed-rotor tachometer detection. This toothed-rotor tachometer has disadvantages because its
fix to the rotor of the motor and reassemble the motor is required. 2
Figure 1.1 Toothed-rotor tachometer detection
The other type of tachometer that commonly used in industrial control application is optical rotary encoder. This instrument used a photo sensor and a disc
which will be montage on the rotating shaft. The rotating disc has a narrow radial slit which allows light from LED go through the disc. Several photodiodes which are
placed behind the slit will detected the light and produced modulated light beam in form of voltage pulses. This voltage signal will be amplified and generated into
digital waveforms suitable for subsequent process. Figure 1.2 has shown optical rotary encoder.
The disc of the optical rotary encoder has to be assembled perpendicular to the rotating shaft of the motor. It must be tight up to the shaft to reduce disc shaking
during rotating that can effect the detection of light beam. Furthermore, the disc has a weight and that can affect minor error to the result. At this point of view, the infrared
tachometer sensor has advantage compared to the optical rotary encoder. 3
Figure 1.2 Optical Rotary Encoder
The infrared tachometer sensor needs only a reflector which have black and white stripe. This sensor is typical light source used as a sensor in hobby robot to
sense unclear object. The basic principle of Infrared sensor is based on an emitter Infrared sensor and an receiver Infrared sensor where it’s usually attach side by side
and point them to a reflective surface. This emitter Infrared sensor and a receiver Infrared sensor will put closer with the motor, so that, it will point to rotation of
motor. From that, the receiver infrared sensor will detect the changes color at the motor’s fan blade.
The motor shaft will be covered with the reflector and the infrared sensor is placed at the distance 0.5cm from the reflector. The output voltage pulses received
from light detector is around 100uV – 10mV. One complete cycle of the voltage
pulse mean one revolution of the rotating shaft. This one revolution needs to be counted until a minute to get the angular speed of revminute. Input voltage for the
PIC microcontroller chip only 5V. The calculation for counting the rpm and display output at LCD would write using C Language. Then, it will compile the code to
generate the HEX file and simulation in Source Boost Debugger Mode. A LCD display is used to shows the speed of the motor in value of revmin. Figure 1.3 has
shown Infrared sensor detection. 4
Figure 1.3 Infrared sensor detection
1.2 Objectives
Kategori