Design Of High-precision Ultrasonic Heat Meter Based On Time-difference Method

Heat Meter is used to measure and display the energy that is released or absorbed by heat exchange system.With the characteristic of high measurement accuracy,long service life,low requirements on the measurement environment,ultrasonic calorimeter is widely used in heat metering.In order to solve the problem of the measurement precision and stability in the condition of small flow rate,this dissertation designs a kind of ultrasonic heat meter which is based on time-difference method.The main contents of this dissertation are as follows.Firstly,this dissertation introduces the different measuring methods of temperature and flow.On the basis of analyzing the advantages and disadvantages of various measurement methods and the technical characteristics of heat meter,this dissertation uses time-to-digital conversion technology to complete the design of time difference ultrasonic heat meter.Next,this dissertation describes detailedly the hardware circuit design of ultrasonic heat meter.Time interval measurement module and temperature measurement module choose a resolution of 65 ps time difference measurement chip TDC-GP2 to complete the circuit design.In the design of the flow measurement circuit,the driving circuit is used to amplify the drive signal and filter the clutter,and the signal processing circuit is used for ultrasonic signal level conversion.Analog switch circuit realizes the direction of ultrasonic transmission by controlling the receiving and transmitting state of the sensor.Finally,this dissertation describes detailedly the software design of ultrasonic heat meter.Time interval measurement module adopts direct-counting method and tap-delay-line method to complete the ultrasonic propagation time measurement in fluid and the capacitor discharge time measurement.In order to achieve the effective calculation of heat value,the Letts criterion and Mean filter are used to eliminate the gross errors of measurement data in the host computer data processing program.The calculation results are displayed on the man-machine interface of the host computer software.On the basis of completing the design and debug of software program and hardware circuit,this dissertation builds the test environment to perform the flow and temperature measurement experiment under the condition of dynamic and static flow.The experimental results verify the system's flow and temperature measurement functions.This design adopts dual channel pulse generator to simulate flow and temperature measurement experiment environment.After calibration,the results show that the time interval measurement precision can reach 0.0015% of the setting value.