Drive techniques for a digital flowmeter

Abstract

Drive techniques for a digital flowmeter are described. The drive techniques account for delays caused during digital signal processing of sensor signals that correspond to a motion of a flowtube, as well as drive signals that impart motion to the flowtube. Such delays may be caused by a variety of factors, including delays associated with analog/digital conversion of the signals and/or filtering of the signals. The techniques include open-loop techniques and closed-loop techniques, which can be used separately or together during the start-up and operation of the digital flowmeter.

What is claimed is:  
     
         1 . A method comprising: 
 inputting a first signal at a flowmeter, the first signal corresponding to a vibration of a flowtube;    compensating for a delay of the first signal, the delay being associated with a digital element associated with the flowmeter; and    outputting a second signal from the flowmeter, the second signal corresponding to the vibration of the flowtube.    
     
     
         2 . The method of  claim 1  wherein inputting the first signal comprises: 
 inputting a first sensor signal and a second sensor signal; and  
 calculating the first signal as a weighted sum of the first sensor signal and the second sensor signal.  
 
     
     
         3 . The method of  claim 1  wherein the vibration is at a natural resonant frequency of the flowtube.  
     
     
         4 . The method of  claim 1  wherein the digital element includes at least one of an analog-to-digital and digital-to-analog converter.  
     
     
         5 . The method of  claim 1  wherein the digital element includes a filter.  
     
     
         6 . The method of  claim 5  wherein the filter is implemented as a software filter.  
     
     
         7 . The method of  claim 5  wherein the filter includes an elliptical filter.  
     
     
         8 . The method of  claim 7  wherein the elliptical filter is implemented in a software routine.  
     
     
         9 . The method of  claim 1  wherein compensating for the delay of the first signal comprises: 
 buffering the first signal at a buffer, the buffer storing a first cycle and a second cycle of the first signal;  
 selecting a value from the first cycle of the first signal; and  
 outputting the value from the buffer.  
 
     
     
         10 . The method of  claim 9  wherein outputting the second signal from the flowmeter comprises: 
 initiating a third signal beginning with the value;  
 passing the third signal through the digital element; and  
 outputting the second signal from the digital element.  
 
     
     
         11 . The method of  claim 1  wherein inputting the first signal comprises filtering the first signal to obtain a filtered signal, wherein the filtered signal substantially reduces components of the first signal having a frequency outside of a pre-determined range from a resonant frequency of the flowtube.  
     
     
         12 . The method of  claim 11  wherein the components include harmonics of the first signal.  
     
     
         13 . The method of  claim 11  wherein outputting the second signal from the flowmeter comprises synthesizing the second signal to be in phase with the first signal.  
     
     
         14 . The method of  claim 12  wherein outputting the second signal from the flowmeter comprises synthesizing the second signal as a sine wave in phase with the first signal.  
     
     
         15 . The method of  claim 12  wherein outputting the second signal from the flowmeter comprises synthesizing the second signal as a plurality of sinewaves, each having individually-controlled signal characteristics.  
     
     
         16 . The method of  claim 1  wherein compensating for the delay of the first signal comprises: 
 detecting a first pre-determined marker on the filtered signal;  
 calculating an actual frequency of the filtered signal, based on samples associated with the filtered signal; and  
 waiting a total wait time for outputting the second signal, based on the actual frequency.  
 
     
     
         17 . The method of  claim 16  wherein the first pre-determined marker is a negative-to-positive zero-crossing of the filtered signal.  
     
     
         18 . The method of  claim 16  wherein waiting the total wait time comprises: 
 calculating a count number of samples of the filtered signal;  
 detecting a second pre-determined marker on the filtered signal; and  
 waiting the count number after the second marker.  
 
     
     
         19 . The method of  claim 18  wherein the second pre-determined marker is a negative-to-positive zero-crossing of the filtered signal.  
     
     
         20 . The method of  claim 16  wherein waiting the total wait time comprises: 
 calculating a count number of samples of the filtered signal; and  
 waiting the count number after the first marker.  
 
     
     
         21 . The method of  claim 16  wherein outputting the second signal from the flowmeter comprises: 
 waiting the total wait time; and  
 synthesizing the second signal.  
 
     
     
         22 . The method of  claim 1  wherein compensating for the delay of the first signal comprises: 
 inputting the second signal from an output of the flowmeter to an input of the flowmeter;  
 comparing the second signal to the first signal to determine a phase difference between the second signal and the first signal; and  
 outputting a revised second signal from the flowmeter that is adjusted from the second signal, based on the phase difference.  
 
     
     
         23 . The method of  claim 22  wherein the first signal includes a first sensor signal associated with a first sensor and a second sensor signal associated with a second sensor, and the second signal includes a first drive signal associated with a first driver and a second drive signal associated with a second driver.  
     
     
         24 . The method of  claim 23  wherein comparing the second signal to the first signal comprises: 
 receiving the first sensor signal and the first drive signal at a first multiplexer;  
 outputting a first multiplexed signal from the first multiplexer;  
 receiving the second sensor signal and the second drive signal at a second multiplexer;  
 outputting a second multiplexed signal from the second multiplexer; and  
 comparing the first multiplexed signal and the second multiplexed signal, to thereby determine the phase difference.  
 
     
     
         25 . The method of  claim 1  wherein inputting the first signal at the flowmeter comprises computing measurements associated with a material within the flowtube in parallel with the compensating for the delay of the first signal.  
     
     
         26 . A digital flowmeter, comprising: 
 a vibratable flowtube;    a sensor connected to the flowtube and operable to relay information about a motion of the flowtube by way of a sensor signal;    a driver connected to the flowtube and operable to impart motion to the flowtube by way of a drive signal; and    a digital control and measurement system connected to the driver and the sensor, the digital control and measurement system comprising circuitry to maintain the sensor signal and the drive signal substantially in phase with one another.    
     
     
         27 . The digital flowmeter of  claim 26 , wherein the sensor signal includes a weighted sum of a first sensor signal and a second sensor signal.  
     
     
         28 . The digital flowmeter of  claim 26  wherein the digital control and measurement system includes analog-to-digital or digital-to-analog converters.  
     
     
         29 . The digital flowmeter of  claim 26  wherein the digital control and measurement system includes a filter.  
     
     
         30 . The digital flowmeter of  claim 26  wherein the digital control and measurement system comprises: 
 a buffer operable to store a first cycle and a second cycle of the sensor signal; and  
 a processor operable to select a value from the first cycle of the sensor signal.  
 
     
     
         31 . The digital flowmeter of  claim 30  wherein the digital control and measurement system is further operable to: 
 initiate a digital drive signal beginning with the value;  
 convert the digital drive signal to an analog drive signal; and  
 output the analog drive signal as the drive signal.  
 
     
     
         32 . The digital flowmeter of  claim 26  further comprising a filter operable to filter the sensor signal to obtain a filtered signal, wherein the filtered signal does not include signals having a frequency outside of a pre-determined range from a resonant frequency of the flowtube.  
     
     
         33 . The digital flowmeter of  claim 32  wherein the digital control and measurement system is further operable to synthesize the drive signal as a sine wave.  
     
     
         34 . The digital flowmeter of  claim 33  wherein the digital control and measurement system is further operable to: 
 detect a first pre-determined marker on the filtered signal;  
 calculate an actual frequency of the filtered signal, based on samples associated with the filtered signal; and  
 wait a total wait time for outputting the second signal, based on the actual frequency.  
 
     
     
         35 . The digital flowmeter of  claim 34  wherein the first pre-determined marker is a negative-to-positive zero-crossing of the filtered signal.  
     
     
         36 . The digital flowmeter of  claim 34  wherein the digital control and measurement system determines the total wait time by: 
 calculating a count number of cycles of the filtered signal;  
 detecting a second pre-determined marker on the filtered signal; and  
 waiting the count number after the second marker.  
 
     
     
         37 . The digital flowmeter of  claim 36  wherein the second pre-determined marker is a negative-to-positive zero-crossing of the filtered signal.  
     
     
         38 . The digital flowmeter of  claim 26  wherein the digital control and measurement system is operable to compare the sensor signal and the drive signal, to thereby determine a phase difference therebetween, and is further operable to cause the driver to apply the drive signal with a phase altered by an amount determined by the phase difference.  
     
     
         39 . The digital flowmeter of  claim 38  wherein the digital control and measurement system further comprises a multiplexer that is operable to input the sensor signal and the drive signal and output a combined signal, and wherein the combined signal is analyzed by the digital control and measurement system to determine the phase difference.  
     
     
         40 . A digital flowmeter, comprising: 
 a vibratable flowtube;    a driver connected to the flowtube and operable to impart motion to the flowtube by way of an analog drive signal;    a sensor connected to the flowtube and operable to sense a motion of the flowtube by way of an analog sensor signal; and    a digital transmitter connected to the sensor and the driver, the digital transmitter including a digital component and operable to perform signal processing related to the analog sensor signal and the analog drive signal, wherein the signal processing compensates for a delay associated with the digital component to ensure that the analog sensor signal and the analog drive signal are substantially in phase with one another.    
     
     
         41 . The digital flowmeter of  claim 40 , wherein the digital transmitter comprises: 
 an analog-to-digital converter operable to convert the analog sensor signal into a first digital signal; and    a digital-to-analog converter operable to convert a second digital signal into the analog drive signal.    
     
     
         42 . The digital flowmeter of  claim 41  wherein the digital transmitter further comprises a digital controller operable to input the first digital signal, perform the signal processing thereon, and output the second digital signal.  
     
     
         43 . The digital flowmeter of  claim 42  wherein the digital controller further comprises a buffer operable to buffer the first digital signal, and further wherein the signal processing includes selecting a value of the first digital signal from the buffer for outputting as a beginning of the second digital signal.  
     
     
         44 . The digital flowmeter of  claim 42  wherein the digital controller further comprises a filter operable to filter the analog sensor signal, and the digital transmitter further comprises a synthesizer operable to synthesize the second digital signal.  
     
     
         45 . The digital flowmeter of  claim 44  wherein the digital transmitter is operable to determine a filter delay associated with the filter, and the synthesizer is operable to synthesize the second digital signal with a timing that reflects the filter delay.  
     
     
         46 . The digital flowmeter of  claim 42  wherein the digital transmitter is operable to compare the analog sensor signal and the analog drive signal, to thereby determine a phase difference therebetween, and is further operable to cause the driver to alter a phase of the analog drive signal by an amount determined by the phase difference.