Design of automatic positioning device for noise measurement based on 80C552 and DME2000

1 Introduction

Noise has serious harm to human health, so how to reduce the harm of noise has become an urgent task. Accurate measurement and analysis of noise will provide an important basis for controlling noise sources, improving product design processes, formulating environmental protection measures and relevant laws. With the rapid development of new technologies such as office automation and computers, people are also paying more attention to the noise treatment of office automation equipment. Noise is an important indicator in the corresponding environmental protection standards. In terms of noise measurement, the distributed sampling method is mostly used for measurement. However, the selection of measurement points is only based on a simple projection distance measurement method. Each measurement requires manual measurement and adjustment of the distance between the sound level meter measuring head and the object being measured, which is labor-intensive and time-consuming.

This paper introduces a noise automatic positioning system that can reduce the workload and has high accuracy. It is an automatic positioning device composed of an 80C552[1] single-chip microcomputer and a DME2000[2] photoelectric distance detector to measure noise. The LCD displays the working status and has a high performance-price ratio, which is of great promotion value.

2 Basic principles

(1) Physical measurement parameters of noise

Noise is the same as sound, except that noise is a sound with more complex frequencies. The strength of noise is indicated by the commonly used sound pressure level, sound intensity level and sound power level, and the level of noise is indicated by the spectrum or frequency. In actual measurement, sound power is generally used to indicate noise characteristics:

Lp= 10lgP/P0

Where: Lp is the sound power level (dB);

p is the sound power;

p. is the reference sound power (10-12W).

However, in actual measurement, sound power is not directly measured, but can only be calculated from the measured sound pressure level under specific test conditions. In the measurement of office automation products, the free field condition engineering method is generally used. Under the free sound field condition on the reflecting surface, the relationship between the sound pressure level and the sound power level is:

Lp=Lp+10lgS/S0-K2

Where: Lp is the average sound pressure level of the test surface (dB);

S is the test surface area (m2);

s. is the reference surface area (1 m2);

K2 is the correction value caused by the environment.

(2) Test method

In the noise test, taking the noise test of the electrostatic copier as an example, the measurement point is selected to use a minimum rectangular hexahedron surface (or sphere, hemisphere) that can just cover the sound source as the reference measurement surface. The specific measurement principle is: as long as the difference between the maximum and minimum sound pressure levels in the measurement point does not exceed the number of measurement points.

(3) Automatic positioning device

The basic principle of the automatic positioning system is shown in Figure 1. The distance sensor is used to measure the distance of the object to be measured (copier), and the stepper motor is controlled by the single-chip microcomputer to adjust the distance between the sound level meter and the object to be measured. The distance sensor uses the DME2000 photoelectric distance detector. The DME2000 emits red level 2 light (safe for human eyes). The distance value can be transmitted through analog quantity or RS232. Its direct reflection mode can be used to measure in a non-contact manner and is not affected by the reflection of the object. Almost any surface of the object, such as hard, liquid, powdery objects, can be measured. The detection analysis degree is 0.125mm and the accuracy is ±5mm. The measurement error increases as the reflectivity of the object being measured decreases, but this can be compensated by an integrator with a selectable integration factor.

The reversible distance can be adjusted by using a stepper motor. According to the principle of the stepper motor, the direction of rotation will be different if the order of powering on each phase winding of the stepper motor is different. The main tasks of the stepper motor control program are: to determine the direction of rotation, to send control pulses in sequence, and to determine whether the pulse signals to be sent have been sent. Assume that the total step length of the stepper motor is placed in register R4, and the direction flag is stored in the flag bit F0 (i.e. PSW.5H) in the program status register. When F0 is 0, it means that the stepper motor is rotating forward; when F0 is 1, it means that the stepper motor is rotating reversely. The end flag 00H word is stored in the 2DH unit. The distance of each point can be selected by the keyboard and displayed by the LCD. The list of the stepper motor control program is as follows:

CONTROLl: PUSH A
MOV R4, #N
CLR C
ORL C, PSW. 5
JC ROTE
MOV R0，#20H
AJMP LOOP
ROTE: MOV R0，#H27
LOOP: MOV A，@R0
MOV P1,A
ACALL DELAY
INC R0
MOV A，#00H
ORL A，@R0
JZ TPL
LOOP1: DJNZ R4,LOOP
POP A
RET
TPL: MOV A,R0
CLR C
SUBB A，#61
MOV R0,A
AJMP LOOP1
DELAY: MOV R2,#M
DELAY1: MOV A,#M1
LOOP2: DEC A
JNZ LOOP2
DJNZ R2,DELAY1
RET

The working flow chart of the automatic positioning device controlled by the single-chip microcomputer is shown in Figure 2 and the flow chart of the stepper motor control is shown in Figure 3.


3 Conclusion

This paper introduces the noise measurement automatic positioning device composed of 80C552 single chip microcomputer and DME2000. It can save the trouble of manual distance measurement each time and has high accuracy. It is more convenient to use LCD to display the automatic positioning situation. It can not only be used as an office automation noise measurement device but also be used for large machinery monitoring.