【正文】 ed. 1,40 kHz ultrasonic pulse generated with the launch Ranging system using the ultrasonic sensor of piezoelectric ceramic sensors UCM40, its operating voltage of the pulse signal is 40kHz, which by the singlechip implementation of the following procedures to generate. puzel: mov 14h, 12h。s arrival is based on thresholding the received signal with a fixed reference. The threshold is chosen well above the noise level, whereas the moment of arrival of an echo is defined as the first moment the echo signal surpasses that threshold. The intensity of an echo reflecting from an object strongly depends on the object39。 附件 2：外文原文 （復(fù)印件） Ultrasonic distance meter Document Type and Number:United States Patent 5442592 Abstract:An ultrasonic distance meter cancels out the effects of temperature and humidity variations by including a measuring unit and a reference unit. In each of the units, a repetitive series of pulses is generated, each having a repetition rate directly related to the respective distance between an electroacoustic transmitter and an electroacoustic receiver. The pulse trains are provided to respective counters, and the ratio of the counter outputs is utilized to determine the distance being measured. Publication Date:08/15/1995 Primary Examiner:Lobo, Ian J. OF THE INVENTION This invention relates to apparatus for the measurement of distance and, more particularly, to such apparatus which transmits ultrasonic waves between two points. Precision machine tools must be calibrated. In the past, this has been acplished utilizing mechanical devices such as calipers, micrometers, and the like. However, the use of such devices does not readily lend itself to automation techniques. It is known that the distance between two points can be determined by measuring the propagation time of a wave travelling between those two points. One such type of wave is an ultrasonic, or acoustic, wave. When an ultrasonic wave travels between two points, the distance between the two points can be measured by multiplying the transit time of the wave by the wave velocity in the medium separating the two points. It is therefore an object of the present invention to provide apparatus utilizing ultrasonic waves to accurately measure the distance between two points. When the medium between the two points whose spacing is being measured is air, the sound velocity is dependent upon the temperature and humidity of the air. It is therefore a further object of the,present invention to provide apparatus of the type described which is independent of temperature and humidity variations. OF THE INVENTION The foregoing and additional objects are attained in accordance with the principles of this invention by providing distance measuring apparatus which includes a reference unit and a measuring unit. The reference and measuring units are the same and each includes an electroacoustic transmitter and an electroacoustic receiver. The spacing between the transmitter and the receiver of the reference unit is a fixed reference distance, whereas the spacing between the transmitter and receiver of the measuring unit is the distance to be measured. In each of the units, the transmitter and receiver are coupled by a feedback loop which causes the transmitter to generate an acoustic pulse which is received by the receiver and converted into an electrical pulse which is then fed back to the transmitter, so that a repetitive series of pulses results. The repetition rate of the pulses is inversely related to the distance between the transmitter and the receiver. In each of the units, the pulses are provided to a counter. Since the reference distance is known, the ratio of the counter outputs is utilized to determine the desired distance to be measured. Since both counts are identically influenced by temperature and humidity variations, by taking the ratio of the counts, the resultant measurement bees insensitive to such variations. DESCRIPTION of ultrasonic distance measurement 1, the principle of piezoelectric ultrasonic generator Piezoelectric ultrasonic generator is the use of piezoelectric crystal resonators to work. Ultrasonic generator, the internal structure as shown in Figure 1, it has two piezoelectric chip and a resonance plate. When it39。因此，它不僅可用于移動(dòng)機(jī)器人，還可用在其它檢測(cè)系統(tǒng)中。 五、結(jié)論 對(duì)所要求測(cè)量范圍 30cm~200cm 內(nèi)的平面物體做了多次測(cè)量發(fā)現(xiàn) ，其最大誤差為，且重復(fù)性好。 系統(tǒng)初始化后就啟動(dòng)定時(shí)器 T1 從 0開(kāi)始計(jì)數(shù)，此時(shí)主程序進(jìn)入等待，當(dāng)?shù)竭_(dá)定時(shí)時(shí)間時(shí) T1 溢出進(jìn)入 T1 中斷服務(wù)子程序；在 T1 中斷服務(wù)子程序中將啟動(dòng)一次新的超聲波發(fā)射，此時(shí)將在 引腳上開(kāi)始產(chǎn)生 40KHz 的方波，同時(shí)開(kāi)啟定時(shí)器 T0計(jì)時(shí)，為了避免直射波的繞射，需要延遲 1ms 后再開(kāi) INT0 中斷允許； INT0 中斷允許打開(kāi)后，若此時(shí)出現(xiàn)低電平則代表收到回波信號(hào)，將提出中斷請(qǐng)求進(jìn)入 INT0 中斷服務(wù)子程序，在 INT0 中斷服務(wù)子程序中將停止定時(shí)器 T0計(jì)時(shí)，讀取定時(shí)器 T0 時(shí)間值到相應(yīng)的存儲(chǔ)區(qū)，同時(shí)設(shè)置接收成功標(biāo)志；主程序一旦 檢測(cè)到接收成功標(biāo)志，將調(diào)用測(cè)溫子程序，采集超聲波測(cè)距時(shí)的環(huán)境溫度，并換算出準(zhǔn)確的聲速，存儲(chǔ)到 RAM 存儲(chǔ)單元中；單片機(jī)再調(diào)用距離計(jì)算子程序進(jìn)行計(jì)算，計(jì)算出傳感器到目標(biāo)物體之間的距離；此后主程序調(diào)用顯示子程序進(jìn)行顯示；當(dāng)一次發(fā)射、接收、顯示的過(guò)程完成后，系統(tǒng)將延遲 100ms 重新讓 T1置初值，再次啟動(dòng) T1 以溢出，進(jìn)入下一次測(cè)距。主程序完成初始化工作、各路超聲波發(fā)射和接收順序的控制。 第六步：通過(guò)公式計(jì)算距離 y。測(cè)量過(guò)零時(shí)間與回波的振幅。根據(jù)第二部的數(shù)據(jù)設(shè)定時(shí)間窗。 第四步：設(shè)置 回波放大器的所得來(lái)規(guī)格輸出，假定是 3伏。 第二步：根據(jù)公式改變回波放大器的獲得量直到回?fù)鼙粰z測(cè)到。其部分源程序如下： R