Explosion Proof Type Pyrometer
This classification includes pyrometers designed for blast furnace equipped with explosion proof instrument.
Conditions in furnace are always tough alone with high temperature and high pressure. Limited to the requirements of operation environment and instrument`s structure, thermocouple thermometry would result in inaccurate measurement and lag reaction when works in harsh condition such as frequently temperature changes, large pressure fluctuations and event in vibration.
Since a thermocouple works at the high temperature ( usually 1200 ℃ ~ 1300 ℃) in furnace for long term, the thermocouple junction box also works at high temperature between 100 ℃ to 120 ℃, which will dramatically reduce instrument`s service life to a range from few weeks to few months. It will increases use-cost and maintenance workload.
In order to overcome above shortcomings, our company has designed and produced a serials of specialized infrared temperature measure device to ensure our infrared temperature measuring system works reliably in complex environment.
Explosion Proof Type Pyrometer,Explosion Proof Pyrometer,Stove Use Pyrometer,Pyrometer For Industry Furnace Changzhou Sijie Optoelectronics Technology Co.,Ltd. , https://www.sjinfrared.com
Brushless Motor Structure and Rotation Principles
TIP: Rotor Magnet Demagnetization
Permanent magnets are magnetized by applying a strong magnetic field to magnet materials. Conversely, excessive current flowing through a motor generates a diamagnetic field in the stator, weakening the magnetic force of the rotor magnets. This phenomenon is known as demagnetization.
In Part 3, we’ll explore the differences in structure and rotation principles between brushless motors and compare them to brushed DC motors and AC motors.
Below is a visual representation of the brushless motor structure and its operational principles:
Brushless motors retain the excellent controllability of DC motors but replace their brushes and commutators with electronic components.
### 2.2.1 Brushless Motor Structure
The rotor contains permanent magnets, while the stator houses windings. This arrangement reverses the typical locations of the stator and rotor found in DC motors (as illustrated in Fig. 2.1 from the previous post). In brushed DC motors, the motor starts rotating as soon as current is supplied to its windings via the commutator and brushes. As the motor rotates, the next set of commutator and brush are energized, directing current flow into different windings and maintaining rotation. Brushless motors achieve commutation without brushes or a commutator, relying instead on magnetic pole sensors (such as Hall elements or Hall effect ICs) to detect the position of the permanent magnets and drivers to direct current flow through the windings based on these detections.
### 2.2.2 Brushless Motor Rotation Principles
To explain the rotation principles of brushless motors, we'll use the simplified three-phase, 2-pole model shown in Fig. 2.8.
The rotor magnets have both a north and south pole, each spanning a magnetic pole angle of 180°. Magnetic pole sensors Ha, Hb, and Hc are spaced 120° apart and detect the north pole of the rotor magnets, outputting a signal. On the stator side, the phase-U coil, phase-V coil, and phase-W coil are spaced 120° apart and offset from the magnetic pole sensors by 60°.
When current flows from the drive circuit to the motor, a south pole is generated on the inner diameter side of the stator. Conversely, a north pole is created when the current flows in the opposite direction. Fig. 2.8 shows the state when current flows from phase-U to phase-V.
To explain the motor’s rotation principles, we’ll refer to the rotation sequence shown in Fig. 2.9, assuming the orientation of the rotor magnets in Fig. 2.8 as the initial point (0°).
### 2.2.3 Brushless Motor Characteristics
The stator and rotor positions in brushless motors are inverted compared to those in DC motors. Therefore, the fundamental speed-torque characteristics of brushless motors resemble those of brushed DC motors, as depicted in Fig. 2.10, and the motor rotates at a speed that matches the load torque. If the speed decreases, the torque generated by the motor increases, and a current proportional to the torque flows. Excessive current can cause the magnetic force of the permanent magnets to weaken (demagnetization), and the windings may overheat and burn out. Additionally, the output element and converter on the drive circuit must be capable of handling large currents, leading to larger and more expensive drive circuits.
If the speed increases, the torque generated by the motor decreases, making it unsuitable for use. Operating at higher speeds increases noise from the gearhead combined with the motor and may lead to insufficient gearhead lubrication, affecting lifespan. Due to these considerations, brushless motors limit the maximum current flowing through the motor and the maximum rotation speed. Consequently, the speed-torque characteristics printed in Oriental Motor’s product catalog resemble Fig. 2.11.
Oriental Motor’s motor and driver systems are designed to prevent demagnetization at the current level corresponding to the maximum instantaneous torque.
### 2.2.4 Brushless Motor Features
The features of brushless motors are outlined below.
**Compared to DC Motors:**
- The speed-torque characteristics have the same sloping characteristics as brushed DC motors and offer excellent controllability.
- Since there are no brushes or commutators, there’s no need for periodic maintenance like cleaning abrasion powder or replacing brushes, resulting in a longer lifespan.
- No brushes or commutators mean no electronic noise due to arcs; however, switching noise is generated.
- No mechanical acoustic noise (from brushes) is produced.
- Magnetic pole sensors and drivers are required for operation.
- High-speed accuracy is achieved by detecting the motor’s rotation speed from magnetic pole sensor output and performing feedback control.
- Feedback control allows for the detection of abnormal behavior during operation.
**Compared to Inverter-Controlled Motors and AC Speed Control Motors:**
- The torque remains constant from low to high speeds, providing a large speed ratio for practical purposes.
- At the same output power, brushless motors are more compact and efficient.
- They can operate with a DC power supply.
- High-speed accuracy is achieved by detecting the motor’s rotation speed from magnetic pole sensor output and performing feedback control.
- Feedback control enables the detection of abnormal behavior during operation.
Brushed DC motors are cost-effective and thus used in applications where the required lifespan is relatively short. However, for general industrial use, there is a need for higher reliability in terms of speed accuracy during operation, malfunction detection, and so on, driving the growing popularity of brushless motors. Additionally, due to their compact size, high output power, and efficiency, brushless motors are widely used in devices requiring compactness and light weight, as well as in battery-powered devices.
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This content has been expanded and rewritten to provide a clearer and more detailed explanation of brushless motors, making it more engaging and comprehensive for readers.