在轻工业重复冷却水上的应用轻工业中冷却水流量测量的用途有两种，一种用于流量检测，参与过程控制，以检验水处理设施的供水能力是否满足了主工艺正常生产的要求；另一种用于流量的计量，计量的结果送企业的能源中心，作为企业耗水技术经济指标计算的依据。 Application of ultrasonic flowmeter on repeated cooling water in light industry There are two uses of cooling water flow measurement in light industry, one is for flow detection and participate in process control to verify whether the water supply capacity of the water treatment facility meets the requirements of normal production of the main process ; Another type is used for flow measurement, and the results of the measurement are sent to the energy center of the enterprise as the basis for calculating the technical and economic indicators of water consumption of the enterprise. In the current projects with a high degree of automation, the most commonly used are electromagnetic flowmeters and ultrasonic flowmeters. In the industrial circulating water system, the primary condition for the decision to use an ultrasonic flowmeter is water quality. Industrial circulating water includes industrial net circulating water, demineralized water circulating water, pure water circulating water, turbid circulating water, and mud water containing iron oxide powder particles, which are softened. The conductivity of water circulating water and pure water circulating water is extremely low. Ultrasonic flow meters should be used. Both of the other circulating water quality water flow meters can be used. The properties of the medium itself, including temperature, turbidity, ph, and oil content, have relatively low requirements on the flowmeter. In small-diameter pipes, the ultrasonic flowmeter is more expensive than the electromagnetic flowmeter, and the length of the installed straight pipe section is longer than the electromagnetic flowmeter. In current water treatment facilities, electromagnetic flowmeters are usually used on small-caliber pipes; it is difficult to disassemble the flowmeters on large-caliber pipes, and maintenance and shut-off valves must be installed on the front and rear of the electromagnetic flowmeters, and large-caliber pipes are usually used for circulating water supply. Main pipe, so ultrasonic flowmeter can be used for large diameter pipes.
换能器的电路形式 Circuit form of ultrasonic flowmeter transducer
The ultrasonic generator in the ultrasonic flowmeter has a variety of circuit forms, the most typical of which are the following:
1. Half-bridge type The half-bridge type circuit is relatively simple. The PWM controller is a multifunctional IC (integrated circuit) that doubles as a frequency ultrasonic generator and pulse width modulator, and also integrates some protective circuits. Negative feedback circuit. Generally, TL494 is used, and the output of Ic is supplied to the switching tube after being driven by the signal. The two switch tubes are turned on in turn, and the anti-matching is used for the ultrasonic transducer. There are two ways to adjust the power; the first is to adjust the frequency. Because the ultrasonic transducer has the largest output power at the resonance frequency and its power consumption is large, so when the adjustment frequency is the resonance frequency of the ultrasound transducer, its power is the largest. We can tune the frequency so that the ultrasound transducer deviates from the resonance. Frequency, the power of the ultrasonic transducer will also decrease. The larger the deviation frequency, the greater the power reduction, to achieve the purpose of adjusting power. Another way is to fix the frequency and adjust the duty cycle. When the on-time of the switch is longer, the output power is larger, the on-time is smaller, and the output power is smaller. This form of circuit can also be added with a negative power feedback circuit. When the power supply voltage changes, the duty cycle can be adjusted through feedback to stabilize the output power.
2. Full bridge type Full bridge type is basically similar to the half bridge type. It is through a pair of tubes to switch at the same time to get a variable frequency signal on the load. When TAl and TA2 are turned on and TB1 and TB2 are turned off. Tout gets ① negative ② positive signal; when TB1, TB2 is on and TAl and TA2 are off, Tout gets ① positive ② negative signal, and then cycle, get an alternating power signal at Tout ①, ②. The power adjustment of the full-bridge ultrasonic generator can also be divided into two cases, similar to the half-bridge type. The working principle of automatic tracking of power control frequency is in the application of ultrasonic power. Changes in the temperature, stiffness, and load of the vibration system cause the resonance frequency of the system to drift, and whether the vibration system can always be in resonance is an ultrasonic application. The key is whether to proceed and the original quantity is good or bad, so the speed and accuracy of automatic frequency tracking and tracking are of vital importance. The ultrasonic power source adopts the power setting frequency tracking method, that is, the sampling load voltage and the flowing current phase source. When the phase is a certain set value, the ultrasonic transducer is purely resistive, and the system works in a resonance state. At present, the most widely used ultrasonic flowmeter is a piezoelectric ceramic plate ultrasonic transducer, which is a circuit near the oscillation frequency point to remove static capacitance. The ultrasonic transducer is a series resonant network. L, C, and R are the dynamic inductance, dynamic capacitance, and dynamic resistance of the ultrasonic transducer, respectively. It can be known from the formula that at resonance, the entire network is equivalent to pure resistance, and the phase difference between voltage and current is zero. Therefore, the phase difference between the voltage and current across the ultrasonic transducer can be obtained through phase comparison. Using the phase difference as a feedback signal to control power and frequency changes can realize automatic tracking of mechanical resonance. The ultrasonic power hardware PIC single-chip microcomputer is the controller of the ultrasonic power. It controls the change of the output power and output frequency by picking up the signals of the ultrasonic transducer and setting the operation panel. 超声波换能器振动的温度、刚度、及负载力等因秦的变化使得系统的谐振频率发生了漂移，而振动系统是否能给始终处于谐振状态是超声能否进行及质量优劣的关键，故须频率自动跟踪及功率自动调整和精度至关重要。 Ultrasonic flowmeter ultrasonic transducer vibration temperature, stiffness, and load force due to Qin changes cause the system's resonance frequency to drift, and whether the vibration system can always be in a resonance state is whether the ultrasound can be performed and the quality is good or bad The key is that automatic frequency tracking and automatic power adjustment and accuracy are essential.