【正文】 ( is the ratio of the specific heats at . at constant volume and constant pressure. Relax appears in the case of relaxation processes and this contribution can be much higher than the viscous part (determined by r/s) and the thermal part (determined by k). If relaxational effects are absent it is obvious that the attenuation increases with the square of the frequency. This behaviour is very important for many technological applications and has to be taken into consideration in industrial equip ment. Because in liquids the ratio X is nearly 1 the second term in equation plays an unimportant role.
Very often heterogeneous systems occur in technical processes. They are plicated multiphase or multiponent systems and can appear in the form of suspensions or emulsions and sometimes contain partially dissolved gases. The sonic parameters depend, in a plex way, on the material parameters of the different phases or ponents. When there are diffusion centres in the system (~ such as solid spheres or gas bubbles) then the following equation can be used to determine the attenuation. (7)R is the radius of the solid spheres or gas bubbles. A very high attenuation may occur at higher frequencies (for particles in the Ixmrange this happens at frequencies higher than 10MHz). Under such conditions measurement under industrial conditions can be impossible.
In gases, the thermal effects (second term in equation (6)) are not negligible and a very high attenuation appears in the ultrasonic frequency range. This can be very troublesome for measurements in heterogeneous systems.
In solids, except for many polymers, the attenuation is in general relatively small. But, if there are diffusing centres or boundary surfaces, a considerable attenuation which depends on frequency in a plete way can occur.
The previously described behaviour of the different phases can enable conclusions to be made about the most useful frequency range for。 } DelayMs(1000)。g39。)。 LCD_Write_Char(10,1,39。039。)。 LCD_Write_Char(8,1,(num%100)/10+39。039。)。 LCD_Write_Char(6,1,39。t39。)。 LCD_Write_Char(4,1,39。g39。)。 LCD_Write_Char(2,1,39。e39。)。 } else {LCD_Write_Char(0,1,39。g39。)。 LCD_Write_Char(10,1,39。039。)。 LCD_Write_Char(8,1,39。039。)。 LCD_Write_Char(6,1,39。t39。)。 LCD_Write_Char(4,1,39。g39。)。 LCD_Write_Char(2,1,39。e39。)。 LCD_Write_Char(0,1,39。 num=(num_f/380)。 num=get_ADValue()。 //Timer0中斷 EA=1。 //設(shè)置定時器0初值高8位 TR0=0。 //設(shè)置定時器0為方式1 TL0=0x47。=0xF0。 LCD_Clear()。float num_f。 return (value)。//delay T4 value=valueamp。//delay T3 ADSK=0。//delay T4 } ADSK=1。 ADSK=0。//delay T3 if (ADDO) value++。i++) { ADSK=1。//delay T1 for (i=0。//enable AD while (ADDO)。 ADDO=1。} /************************************* WEIGHT**************************************/unsigned long get_ADValue(void){ uchar i。 } i=9000。m39。)。 //在第1行的第3列顯示個位 LCD_Write_Char(5,0,39。039。)。 //在第1行的第1列顯示百位 LCD_Write_Char(3,0,(S%100)/10+39。039。)。*/ LCD_Write_Char(1,0,39。h39。)。 LCD_Write_Char(2,0,39。i39。)。 } else { //**給1602顯示寄存器賦值(0255)** //***1602液晶顯示0255*** LCD_Write_Char(0,0,39。m39。)。 //在第1行的第3列顯示個位 LCD_Write_Char(5,0,39。39。)。 //在第1行的第1列顯示百位 LCD_Write_Char(3,0,39。39。)。*/ LCD_Write_Char(1,0,39。h39。)。 LCD_Write_Char(2,0,39。i39。)。 if(flag==1||S400) { LCD_Write_Char(0,0,39。 TR0=0。amp。 Timeout=0。 flag=0。amp。 Timeout=0。 TL0=0。 TRIG=0。 i=2。 unsigned int i。 /*顯示開及光標(biāo)設(shè)置*/ }void Timer0(void) interrupt 1 { flag=1。 /*顯示光標(biāo)移動設(shè)置*/ DelayMs(5)。 /*顯示關(guān)閉*/ LCD_Write_Com(0x01)。 LCD_Write_Com(0x38)。 LCD_Write_Com(0x38)。 LCD_Write_Com(0x38)。 }/* 初始化函數(shù)*/ void LCD_Init(void) { LCD_Write_Com(0x38)。 } else { LCD_Write_Com(0xC0 + x)。 s ++。 //表示第一行 } else { LCD_Write_Com(0xC0 + x)。 DelayMs(5)。 EN_CLR。 DataPort= Data。 RW_CLR。 }/* 寫入數(shù)據(jù)函數(shù)*/ void LCD_Write_Data(unsigned char Data) { while(LCD_Check_Busy())。 _nop_()。 EN_SET。 //忙則等待 RS_CLR。 0x80)。 EN_SET。 EN_CLR。 RS_CLR。 DelayUs2x(245)。} /* uS延時函數(shù)，含有輸入?yún)?shù) unsigned char t，無返回值 unsigned char 是定義無符號字符變量，其值的范圍是 0~255 這里使用晶振12M，精確延時請使用匯編,大致延時 長度如下 T=tx2+5 uS */void DelayUs2x(unsigned char t){ while(t)。i10。void delay(){ unsigned int i。unsigned char frq。define DataPort P0 //數(shù)據(jù)端口define RS_CLR RS=0 define RS_SET RS=1define RW_CLR RW=0 define RW_SET RW=1 define EN_CLR EN=0define EN_SET EN=1bit flag。sbit ADDO = P3^5。sbit TRIG=P3^3。 //控制端口 sbit RW = P2^4。希望在今后的學(xué)習(xí)中進(jìn)一步完善，使系統(tǒng)功能更加可靠。不過本設(shè)計依然存在不足之處，比如說超聲波測距太靈敏，人體只要稍微動一下就會引起測量高度的微小變化，無法得出穩(wěn)定數(shù)值；，實際上為了稱出來的數(shù)據(jù)精準(zhǔn)，精度只有1kg。開 始判忙函數(shù)（忙則等待）寫入命令函數(shù)寫入數(shù)據(jù)函數(shù)清屏函數(shù)寫入字符串函數(shù)寫入字符函數(shù)初始化函數(shù)結(jié) 束 液晶顯示模塊程序流程圖結(jié) 論本次設(shè)計基本上達(dá)到了設(shè)計要求，使用非接觸式的超聲波測量距離，通過壓力傳感器稱重輸出電壓經(jīng)過AD轉(zhuǎn)換可以實現(xiàn)人體重量的測量，使用1602液晶可以完整顯示身高體重測量值。第一個時鐘脈沖的上升沿將讀出輸入24位數(shù)據(jù)的最高位，直到第24個時鐘脈沖完成，24位輸出數(shù)據(jù)從最高位至最低位逐位輸出完成。溢出？關(guān)閉定時器0計算距離S=(TH0*256+TL0)/58不顯示數(shù)值S250 ？顯示距離值S結(jié) 束Flag=0？Flag=1 超聲波測高部分程序流程圖 測體重程序設(shè)計壓力傳感器稱體重模塊核心部分是AD轉(zhuǎn)換，在AD轉(zhuǎn)換編程中，當(dāng)數(shù)據(jù)輸出管腳ADDO為高電平時，表明AD轉(zhuǎn)換器還未準(zhǔn)備好輸出數(shù)據(jù)，此時串口時鐘輸入信號ADSK應(yīng)為低電平。溢出？Flag=0并且開啟定時器0中斷（ECHO==1）amp。開始定時器和中斷初始化（ECHO==0）amp。液晶顯示初始化使用標(biāo)準(zhǔn)初始化過程，其初始化過程如下所示：延時15mS，寫指令38H（不檢測忙信號），延時5mS，寫指令38H（不檢測忙信號），延時5mS，寫指令38H（不檢測忙信號），（以后每次寫指令、讀/寫數(shù)據(jù)操作均需要檢測忙信號），寫指令38H：顯示模式設(shè)置，寫指令08H：顯示關(guān)閉，寫指令01H：顯示清屏，寫指令06H：顯示光標(biāo)移動設(shè)置，寫指令0CH：顯示開及光標(biāo)設(shè)置。初始化函數(shù)模塊主要包括定時器及中斷的初始化，加上液晶顯示的初始化程序。[8]： 讀操作時序 寫操作時序3 系統(tǒng)軟件設(shè)計 單