Based on Hall sensor for DC Motor Speed Measurement System

With the rapid evolution of SCM, in particular the emergence of cost-effective single chip, speed measurement commonly used to control the microcontroller as the core digital, intelligent systems. This paper introduces a C8051F060 MCU as the master controller by the use of Hall sensors to measure the DC motor speed measurement system.

1 speed measurement and control principles

1.1 Speed Measurement principle

A lot of speed measurement method, according to pulse count to achieve speed measurement methods are M method (frequency method), T method (measurement cycle method) and the MPT Act (frequency cycle method), the system uses the M method (measuring frequency method). As the speed of revolutions per unit time is measured in the transformation process in the majority of regular repetitive motion. According to Hall-effect theory, a piece of permanent magnet fixed to the turntable motor shaft edge, turntable with the measurement axis, magnet synchronous rotation will be followed in the dial below the installation of a Hall device, turntable with the axis, the subject magnetic field generated by the impact of Hall device output pulse signal is proportional to its frequency and speed. Pulse signal and the motor cycle has the following relationship:

Based on Hall sensor for DC Motor Speed Measurement System

The formula: n is the motor speed; P for the motor number of the rounds of the pulse; T for the output square wave signal period

According to equation (1) can calculate the speed of DC motor.

Hall devices made of semiconductor materials by a sheet, in the direction perpendicular to the plane is applied to the external magnetic field B, in the plane along the direction of both ends of the external electric field increases, the movement of electronic in a magnetic field, resulting in the device's two sides electric potential generated between the Hall. Its size and the size of the external magnetic field and current in proportion. Hall switch sensor because of its small size, non-contact, dynamic characteristics of a good, long service life, so in the field of measuring rotational speed of rotating objects has been widely used. Here the company used the United States Shipulage (SPRAGUE) 3000 production of Hall switch sensor 3013, which is a silicon monolithic integrated circuit, the device contains an internal voltage regulator, Hall-potential generator, amplifier, Smith special trigger and open collector output circuit with wide operating voltage range, high reliability and simple external circuit "Exports level can be compatible with the characteristics of various digital circuits.

1.2 The principle of speed control

DC motor speed and the voltage applied to the ends of the size of the motor, you can use C8051F060-chip D / A converter DAC0 DC output control voltage to control motor speed. Here a simple proportional controller algorithm (simple plus one, minus one method). Proportional regulator output system formula:

Based on Hall sensor for DC Motor Speed Measurement System

Type in: Y for the regulator's output; e (t) as the regulator input, usually deviation; Kp the proportional coefficient.

From (2) can be seen, adjust the output Y and input bias value e (t) is proportional to. Therefore, as long as the deviation e (t) appeared to arise in proportion with the regulation, has the characteristics of regulation time, which is a basic regulation law. In addition to the proportion of the size of regulation and the deviation e (t) the outside, depending on the ratio coefficient Kp, the larger the proportion of adjustment coefficient, the stronger regulation, the greater the dynamic characteristics. Conversely, the smaller the scale factor, the weaker regulation. For most of the inertia, Kp is too large will cause oscillation. The main disadvantage of adjusting the proportion of static error is present, the disturbance of inertia, Kp is too large will cause oscillation. For larger disturbances, inertia is relatively large systems, the use of a simple proportional controller on the difficult balance between dynamic and static characteristics, requires the use of more complex rules regulating PI (proportional integral regulator) or PID (proportional, integral, differential regulation device) algorithm.

2 System hardware and software design

2.1 Hardware Design

The system uses the MCU C8051F060 as the main controller, use the Hall sensor measuring motor speed, by 7079 the final results in the LED display. In addition, it can be adjusted control motor speed, hardware

Pulse controller C8051F060 major collection of speed, 16 for the timer counter counting time, Comparison operations, chip integrated 12-bit DAC0 control the speed, and display interface chip by 7279 digital display and many other features.

System uses an external crystal oscillator, system clock SYSCLK is equal to 18432000, T0 time 1 ms, initialization TH0 = (-SYSCLK / 1 000) "8; TL0 =- SYSCLK / 1 000. Wait 1 s to output rotational speed pulse number N, calculate the value of motor speed. The speed value within 1 s 1 min converted to the value of the motor speed, and the LED on the output measurements.

2.2 Software Design

The system uses the C8051F060 the INT0 interrupt on speed pulse counting. Timer T1 work on the external event count mode of the speed pulse counting; T0 timer mode works in all the work in the way of one. Once every 1 s count time, this value shall be pulse frequency, according to equation (1) calculates the motor speed. As the DC motor speed and processing facilities on the size of the voltage across the motor, so the actual measured speed value compared with the preset speed value, if the speed is greater than the value of the default values decrease DAC0, if less than The default value of speed speed adjustment to increase the value of DAC0 motor speed until the speed value equal to preset value, thus achieving the control of motor speed, and T0 interrupt the main program flow chart shown in Figure 2,3 .

Based on Hall sensor for DC Motor Speed Measurement System

3 Experimental results

First of all, the software is given the default speed that the value of a given constant speed, observe speed stable numerical seven-segment digital tube, comparing the measured speed value and the default speed and calculating the measurement error, evaluation of measurement accuracy of the test results shown in Table 1. According to the experimental testing and error analysis of measurement error drawn curve, shown in Figure 4. Error analysis shows that the speed measurement error is less than 5%, and with the default speed the smaller the measurement error increases, exponentially decreased as a function of type (3) below.

Based on Hall sensor for DC Motor Speed Measurement System

Based on Hall sensor for DC Motor Speed Measurement System

4 Conclusions

The speed system uses an integrated Hall sensor sensitivity rate signals with fast frequency response, the characteristics of strong anti-interference ability. Hall sensor output signal after signal conditioning, the adoption of SCM on the pulse count to achieve continuous speed monitoring and control, and full use of the microcontroller's internal resources, there is a high cost. After testing and error analysis, the system measurement error within 5%, and the higher the measurement accuracy within the higher speed. Therefore, the speed of the system in general can be applied in the detection and control.