关 键 词：

DZ233 超声波 研究 实现

资源描述：

DZ233超声波热表的研究与实现,DZ233,超声波,研究,实现

内容简介：

AbstractFirstly, the paper introduced the present status and application of heat meters. The reason for using ultrasonic heat meter was given. The paper brought out the target and main tasks of this project.Based on the fundamental principle of the measurement of the heat quality and the technology index of heating system，a design scheme of the noncontact calorimeter for heating system is introduced based on ultrasonic measurement technology ，and the design structures of the hardware and some of software are givenThis calorimeter is nocontact，accurate，and has functions of low power consumption，autocompensation for temperature an d pressureThe design shows that its accuracy class is well ，an d its structure is simple，its price is lower，and its practicability has been validatedHardware circuit was discussed and designed in detail. The controller used high capability and low power wastage C8051F020,for ensure Real-time detect system. For reduce the power wastage of system, all parts of an apparatus for the dispose of received signal are low power waste. The thesis use hardware filtering to improve anti-interference ability. The checkout system adopts liquid crystal display to show results.Key words：ultrasonic； calorimeter；noncontact measurement；single chip processor.Flowmeters - ultrasonic flowmetersDoppler and transit-time flowmeters are two types of ultrasonic flow meters that have been extensively used in liquid applications around the world, certain companies are now applying the transit time method for gas flow measurement applications either flare gas or custody transfer meters for natural gas. We would like to explain the use of ultrasonic flow meters where they apply to liquid measurement and particularly transit time method because it yields much greater accuracies where it can be applied.It is important to know what these two technologies are , and where they should be applied to in the field . Our ultrasonic flowmeter as it is today , has gone through many technological advances, especially those in electronic circuitry and with the power of computers crunch numbers faster.Now more updated signal processing is being used in many transit-time flowmeter designs, battery power up to 15 hours and flow readings obtained within seconds,This has considerably eased the job of the flow survey company and increased customer confidence in ultrasonic meters . Survey companies can now measure more pipes than ever before. Recently our companys flow survey unit reports being able to make more than 35 spot checks of liquid flow rate a day. Both transit time and doppler ultrasonic flowmeters may use clamp-on sensors with their associated assemblies and detect flow rate from the outside of the pipe without stopping the process or cutting through the pipe. The applications for this type of technology are manifold because now we are able to make sure our old or new pump is working to its capacity, gather data for flow balancing , check if our permanently installed meters are measuring incorrectly or are in need of maintainance , or simply clamp on a flow meter where there is no flowmeter or where other flowmeters make it impractical for installation What this ultrasonic flow meter is able to do:The ultrasonic meter can measure water, waste water, hydrocarbon liquids, organic or inorganic chemicals, milk, beer, lube oils and the list goes on. The basic requirement is that the fluid is ultrasonically conductive and has a reasonably well formed flow. Clamp-on ultrasonic flowmeters measure flow through the pipe without any contact with the process media, ensuring that corrosion and other effects from the fluid will not affect the workings of the sensors or electronics.In addition the Eesiflo clamp-on ultrasonic flowmeter simplifies installation and maintenance which is a plus in situations where downtime and set up costs need to be controlled. Whether this flow meter is a portable or permanently installed unit, there are several advantages in using it, such as a redundancy to already installed flowmeters or surveying existing meters in a number of locations throughout a municipality or process plant.Typically an Eesiflo ultrasonic flow meter operates on pipe diameters from 50 mm to 6500 mm and fluid temperatures from -30C to 200C ; and flow rates from 0.01 to 25 m/s. All of our standard models are DUAL CHANNEL as standard. Operators can clamp 2 sets of sensors on the same pipe or other pipes. Flow rates can be added or subtracted from each other . Most competitors will charge additionally for a dual channel featureMeasurement accuracy can be in the range 1 to 3 percent of measured value of 0.5 percent with process calibration depending on the application. The portable microprocessor-based electronics unit provides a local backlit display and has a keypad for setting up and diagnostics . The flowmeter can read flow units in common imperial or metric units , measures flow in both directions, can store up to 100,000 data points internally, give analog or serial outputs and has optional inputs for RTDs and thickness gauges. The Heat quantity option is an excellent tool for the HVAC industry where a T1 and T2 can be applied into the equationThe Electronics unit can log data for measuring sites. It can also provide a PC interface via RS-232 serial communication, and an output of 4-20 mA DC for operating a digital controller, DCS, PLC, or recorder.The flowmeter has a built-in, rechargeable battery and can operate continuously for 15 hours. This is a big difference because now you can measure all day with a portable without losing time and money.Laymans explanation of transit timeThe ultrasonic transducers can be mounted in one of two modes. The upstream and downstream ultrasonic transducers can be installed on opposite sides of the pipe (diagonal mode) or on the same side (reflect mode)The electronics unit will measure internally ,the time it takes for signals to transmit from one transducer to another. At zero flow , we see no difference in time, but when flow is introduced,time for the transmission of signal from the downstream transducer to the upstream transducer will take longer than the upstream to downstream. Hence we will see a time differential which has a relationship with the velocity of the fluid being measured. Knowing the internal diameter of the pipe , we can now calculate a volumetric flow for the liquid.Obviously there are factors such as solid and liquid refractive angles , error transmissions and poor sonic conductivity at times, but the inbuilt software will normally deal with these by telling us how we should space the transducers and by rejecting erroneous data it receives.It is important when installing an ultrasonic transit time flow meter to select a location where we would find the most fully formed flow profile, this means that we should avoid bends and try to install our meters on straight runs of pipe. A rule of thumb in the industry is to give at least 10 diameter lengths upstream and 5 lengths downstream. If we are measuring liquids such as water with known properties and sonic velocities we can further check our measurements by several diagnostic methods. Using the keypad we can see what the actual sonic velocity of water is being measured on our installation. This is one of the simplest and quickest methods.Should we find that we are in a situation where the amount of entrained bubbles or solids is so great that no sonic propagation is possible from one transducer to the other, we simply switch into a Doppler mode measurement by pressing one button on the keypad. The Doppler method relies on the existence of solid particles or bubbles in the liquid being measuredMeasuring in ultrasonic Doppler mode is not the preferred mode for most of the applications where we will find our meters being used, but there are some applications which warrant its use and we therefore apply it.Users and designers of flow metering systems can profit by keeping abreast of new developments. The ultrasonic flowmeter, a recent arrival on the scene, has profited from technological advances, especially those in electronic circuitry. For example, fast Fourier transform (FFT) signal processing is being used in one transit-time flowmeter design. And a supplier of Doppler flowmeters credits proprietary software and superior electronics design with opening up new application areas for this well-known technique. Both types of ultrasonic flowmeters feature clamp-on designs with transducer assemblies that detect flow rate from the outside. Installation entails neither breaks in the line nor interruption of flow. One recommendation is that where practical, the new user experiment with a clamp-on meter to investigate the feasibility of a permanent installation, perhaps with wetted transducers and the requisite changes in piping.Clamp-on types measure flow through the pipe without any wetted parts, ensuring that corrosion and other effects from the fluid will not deteriorate the sensors. A corollary to the above is that clamp-on types simplify and speed up meter installation and minimize maintenance. This design and others are portable, a feature particularly advantageous for backing up an already installed flowmeter or checking out existing meters in a number of locations. Depending on the model, the flowmeters can operate on pipe diameters from 0.5 in. (13 mm) to 20 ft (6 m); fluid temperatures from 40F (40C) to 392F (200C); and flow rates from 1.0 ft/s (0.3 m/s) to 106 ft/s (32 m/s). Measurement accuracy can be in the range of 1% of flow rate, and speed of response can be as fast as 1 s. The handheld, microprocessor-based converter provides a local graphics display and has a keypad for calling up page menus for flow data, trend displays, setting up site parameters, and other requirements. The converter can log data for as many as 20 sites and 40,000 data points. It can also provide a PC interface via RS-232 serial communication, and an output of 420 mA DC for operating a digital controller, DCS, PLC, or recorder. As is true of most such meters, operation is linear and bidirectional. The flowmeter has a built-in, rechargeable battery and can operate continuously for five hours. Advanced digital signal processing improves its performance where the flowing fluid contains air or gas bubbles. Some suppliers offer ultrasonic measurements of both level and flow velocity to calculate flow quantities in open channels with weirs or flumes. Others carry ultrasonic meters especially adapted to measure the flow rate of gases. This class of meter is attractive compared to conventional flow metering methods because, in addition to the points listed above, the meters inherently provide linear calibration; have wide rangeability; induce no pressure drop or disturbance in the flow stream; and may offer the most economical cost of ownership.Basic Operating PrinciplesTo detect flow through a pipe, ultrasonic flowmeters use acoustic waves or vibrations of a frequency 20 kHz. Depending on the design, they use either wetted or nonwetted transducers on the pipe perimeter to couple ultrasonic energy with the fluid flowing in the pipe.Doppler Flowmeters. Doppler flowmeters are named for the Austrian physicist and mathematician Christian Johann Doppler (18031853), who in 1842 predicted that the frequencies of received sound waves depended on the motion of the source or observer relative to the propagating medium. To use the Doppler effect to measure flow in a pipe, one transducer transmits an ultrasonic beam of 0.5 MHz into the flow stream (see Figure 2). Liquid flowing through the pipe must contain sonically reflective materials such as solid particles or entrained air bubbles. The movement of these materials alters the frequency of the beam reflected onto a second, receiving transducer. The frequency shift is linearly proportional to the rate of flow of materials in the pipe and therefore can be used to develop an analog or digital signal proportional to flow rate.The basic equations defining the Doppler flowmeter are:It is essential to carefully follow the manufacturers operating instructions. Early problems with ultrasonic flowmeters were perhaps due, at least in part, to the users not understanding the importance of certain fundamentals such as proper mounting of the transducers on the pipe. The acoustic coupling to the pipe and the relative alignment of the transducers must be retained despite events such as a large change in pipe temperature or unusual vibration.For both Doppler and transit-time flowmeters to indicate true volumetric flow rate, the pipe must always be full. A Doppler meter on a partially full pipe, however, will continue to indicate flow velocity as long as the transducers are both mounted below the liquid level in the pipe.Most manufacturers specify the minimum distance that the meter must be from valves, tees, elbows, pumps, and the like, both upstream and downstream. This is usually expressed in pipe diameters and typically should be 1020 diameters upstream and 5 diameters downstream.Transit-time meters rely on an ultrasonic signals completely traversing the pipe, so the path must be relatively free of solids and air or gas bubbles. Bubbles in particular tend to attenuate the acoustic signals, a problem that has been addressed in the Fuji Portaflow X shown in Figure 1. The units electronic circuitry uses a proprietary Fourier transform technique to provide what is termed an advanced antibubble measurement.Doppler meters, on the other hand, rely on reflectors in the flowing liquid. To obtain reliable measurements, therefore, attention must be given to the lower limits for concentrations and sizes of solids or bubbles. The flow must also be rapid enough to keep these materials in suspension. One manufacturer gives as typical the values of 6 ft/s (1.8 m/s) for solids and 2.5 ft/s (0.75 m/s) for small bubbles.Over the past few years, some suppliers of Doppler meters have introduced models that operate at frequencies 1 MHz. The claim for such units is that they will operate on virtually clean liquids because reflections will occur off the swirls and eddies of the flowing liquid. A cautionary note has been sounded, however, advising prospective users to limit the technique to low concentrations of bubbles and particles.Because in the ope