Abstract: To address the shortcomings in the installation process of Hall sensors in brushless DC motors, a logic signal detection and analysis instrument based on a virtual instrument architecture was designed and implemented to detect the signals from the motor's Hall sensors. An AT89S52 microcontroller was used as the signal acquisition unit, and communication between the microcontroller and a PC was achieved via an RS232 serial port. A graphical interface was designed using VB to analyze the acquired data.
In brushless DC motor (BLDC) applications, Hall effect sensors are commonly used to detect the actual position of the motor rotor, providing a basis for electronic commutation. However, due to manufacturing limitations, the installation of Hall effect sensors may result in physical positional deviations, causing timing errors in electronic commutation and affecting the motor's speed and smoothness. To detect this manufacturing defect, specialized motor testing equipment is used in industry; however, these devices are complex, bulky, and expensive. This paper, based on the design concept of a virtual instrument architecture, designs a low-cost logic signal detection and analysis instrument to detect motor Hall effect sensor signals.
1. System Solution
This design uses an inexpensive 51 microcontroller as the signal acquisition unit. The 51 microcontroller sends the acquired data to the PC via an RS232 serial port. The PC then records, analyzes, and plots the waveforms from this data. Utilizing the P1 port of the 51 microcontroller as the signal sampling port, eight logic signals can be acquired simultaneously. Then, via the RS232 serial port, the eight logic levels acquired at the same time are transmitted to the PC as a single 8-bit byte.
2. Software Components
2.1 Microcontroller Section
The AT89S52 microcontroller is a low-power, high-performance CMOS 8-bit microcontroller. It features 8KB of in-system programmable (ISP) flash memory (erasable and rewritable 1000 times), level 3 program memory encryption, a 256B internal ARM core, 32 programmable I/O lines, three 16-bit timers/counters, eight interrupt sources, and a UART serial channel. The AT89S52 uses port P1 as the sampling port, Timer() as the wait timer, and Timer2 as the serial port baud rate timer. The serial port data communication protocol is: a data transmission rate of 57600 b/s, 8 data bits, 1 stop bit, and no parity bit. After the 51 microcontroller powers on, it continuously samples and transmits data, similar to the "DMA" mode in a computer, which is the microcontroller's main program.
Part 2.2
The program, written in VB on a PC, is used to receive, store, and analyze data via the serial port. It draws on the design concept of "virtual instrument architecture" and aims to complete the required testing functions by operating the PC software, just like operating an electronic instrument that you have defined and designed yourself.
First, the serial port must be initialized. The communication characteristics of the MSComm control must be set to be consistent with those of the 51 microcontroller for normal communication.
After the serial port is initialized, the MSComm control can be used to receive data from the serial port in real time. ONComm is the communication event handling function of the MSComm control. The serial communication program is as follows:
The above is the serial port data receiving program. After receiving the data, the PC needs to process and display it. In this system, the collected signal information is displayed intuitively by drawing the data sampling results.
In addition to the above functions, the PC software also has the ability to save the collected data and retrieve historical samples.
3. Application Examples
Hall effect sensors play a crucial role in brushless DC motor control systems. They detect the position of the rotor poles, providing accurate commutation information to the switching circuit. A phase deviation in the Hall effect sensor will cause a timing error in electronic commutation, affecting the motor's speed and smoothness. A missing phase in the Hall effect sensor's phase will increase the motor's phase current and electromagnetic torque ripple, potentially even burning out the motor. Therefore, Hall effect phase detection is extremely important. This paper applies a designed logic signal detection and analysis instrument to the detection of Hall effect sensor signals in motors. Its hardware circuit is shown in Figure 3.
Brushless DC motors (BLDC) typically have three Hall effect sensors. The three signals generated are sampled by a 51 microcontroller and transmitted to a PC via an RS232 serial port. Receiver and analysis software running on the PC analyzes and displays the acquired signals. After connecting the detection circuit, the motor rotor is manually rotated, and sampling is initiated in the software. After a period of time, sampling stops, and waveforms are obtained. As shown in Figure 4, when the BLDC rotor rotates, the Hall effect signals exhibit a square wave waveform. The positional changes of the three Hall effect signals can be effectively analyzed using the analysis software.
This paper designs a logic signal detection and analysis instrument based on a virtual instrument architecture, which fully utilizes the functions of a microcontroller and a PC. It can simultaneously sample eight signals, store and record a large amount of test data, and effectively analyze and graphically display the detection data. The instrument was successfully applied to the detection of Hall sensor signals in a motor, achieving good results. Due to its simple structure, low cost, wide applicability, and strong scalability, it can be used in various multi-channel signal detection schemes.
