Abstract:
A method for measuring fluid flow includes generating vortices in a fluid and relating the fluid flow to a first set of fluid parameters to obtain a first relationship, and relating the fluid flow to a second set of fluid parameters to obtain a second relationship. The first and second sets of fluid parameters are monitored. A first flow value is calculated from the first set of monitor fluid parameters and the first relationship. The second relationship is adjusted based on the first flow value. The output value is calculated from the second set of monitored fluid parameters and the adjusted second relationship.

Description:
This application is a continuation-in-part of application Ser. No. 08/826,167, filed Mar. 27, 1997, which is hereby incorporated by reference in its entirety, now U.S. Pat. No. 6,170,338. This application relates to applications: VORTEX FLOWMETER WITH SIGNAL PROCESSING, Ser. No. 09/400,503; VORTEX FLOWMETER WITH MEASURED PARAMETER ADJUSTMENT, Ser. No. 09/399,898; and ANCILLARY PROCESS OUTPUTS OF A VORTEX FLOWMETER, Ser. No. 09/399,707, all of which are filed on even date herewith and hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to flowmeters such as vortex shedding meters or swirlmeters which are responsive to a fluid flow. 
     Flowmeters sense the flow of liquids or gasses in conduits and produce a signal indicative of the flow. Under certain circumstances, the presence of an obstacle known alternatively as a shedding bar, bluff body, or vortex generator, in a flow conduit causes periodic vortices in the flow. The frequency of these vortices is directly proportional to the flow velocity in the flowmeter. The shedding vortices produce an alternating differential pressure across the bluff body at the shedding frequency. This differential pressure is converted to an electrical signal by piezoelectric crystals or other differential pressure devices. The magnitude of the differential pressure or electric signal is proportional to ρV 2 , where ρ is the fluid density and V is the fluid velocity. When the ratio of pipe diameter to the size of the bluff body is held constant, the signal magnitude is proportional to ρD 2 F 2 , where D is the inside diameter of the metering pipe and F is the shedding frequency. The vortex flowmeter produces pulses having a frequency proportional to the flow rate. In a swirlmeter, the fluid whose flow rate is to be measured is forced to assume a swirl component by means of swirl blades, the arrangement being such that the swirling motion is transformed into precessional movement to produce fluidic pulses which are sensed to yield a signal whose frequency is proportional to flow rate. See e.g., U.S. Pat. Nos. 3,616,693 and 3,719,080 which disclose examples of swirlmeters and are hereby incorporated by reference.As used herein, “vortex flowmeter” shall include both vortex shedding meters and swirlmeters. 
     The vortex flowmeter is a measurement transmitter that is typically mounted in the field of a process control industry installation where power consumption is a concern. The vortex flowmeter can provide a current output representative of the flow rate, where the magnitude of current varies between 4-20 mA on a current loop. It is also desirable for the vortex flowmeter to be powered completely from the current loop so that additional power sources need not be used. Thus, the vortex flowmeter measurement transmitter should be able to operate with less than 4 mA in order for the transmitter to adhere to this process control industry communication standard. 
     It is known to incorporate a microprocessor into a vortex flowmeter. The microprocessor receives digital representations of the output signal from the vortex sensor and computes desired output quantities based on parameters of the digital representation. For instance, a vortex flowmeter can calculate the mass flow rate through the pipe or conduit. It is desirable to provide the calculated mass flow rate approximately ten times per second. For each new calculation of the mass flow rate, the microprocessor must perform many mathematical steps wherein each mathematical step requires a number of clock cycles, thus limiting the rate at which calculated mass flow rates can be provided. Although it would be desirable to use a more powerful microprocessor, which could perform further calculations to improve accuracy, the microprocessor would require more power than is available from the 4-20 mA industry standard discussed above. 
     Nevertheless, there is a continuing need for a vortex flowmeter having improved accuracy. However, sacrifices should not be made in the update rate nor should power consumption exceed the power available from the current loop. 
     SUMMARY OF THE INVENTION 
     A method for measuring fluid flow includes generating vortices in a fluid and relating the fluid flow to a first set of fluid parameters to obtain a first relationship, and relating the fluid flow to a second set of fluid parameters to obtain a second relationship. The first and second sets of fluid parameters are monitored. A first flow value is calculated from the first set of monitor fluid parameters and the first relationship. The second relationship is adjusted based on the first flow value. The output value is calculated from the second set of monitored fluid parameters and the adjusted second relationship. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a vortex flowmeter in accordance with the present invention. 
     FIG. 1A is a block diagram of a second embodiment of a vortex flowmeter in accordance with the present invention. 
     FIG. 2 is a flow chart illustrating operation of the vortex flowmeter of the present invention. 
     FIGS. 3A and 3B are curves of the compressibility factor as a function of pressure at various temperatures for two fluids. 
     FIG. 4 is a side elevational view of the vortex flowmeter with portions removed. 
     FIG. 5 is a sectional view of the vortex flowmeter taken along lines 5—5 of FIG.  4 . 
     FIG. 6 is an enlarged sectional view of a portion of FIG.  4 . 
     FIG. 7 is a sectional view taken along lines 7—7 in FIG.  6 . 
     FIG. 8 is a side elevational view of a second embodiment of the vortex flowmeter with portions removed. 
     FIG. 9 is a sectional view of the vortex flowmeter taken along lines 9—9 of FIG.  8 . 
     FIG. 10 is a sectional view of a vortex flowmeter with another orientation of a streamlined body. 
     FIG. 11 is a front elevational view of the vortex flowmeter of FIG. 10 with portions removed. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an embodiment of a vortex flowmeter  10  of the present invention. Generally, the vortex flowmeter  10  includes a vortex sensor assembly  11  that includes appropriate mechanical and electrical elements to sense vortices  15  in a fluid  14  that flows through a conduit  16 . The vortex sensor  11  is operably coupled to an electronic circuit  12 . The electronic circuit  12  produces both a 4-20 mA current on a current loop  17  indicative of flow as well as a square wave output F out  having a frequency proportional to fluid flow. 
     The vortex flowmeter  10  includes a vortex meter housing or flowtube  22  having a vortex generator or bluff body  24  located therein. When the fluid  14  flows past the bluff body FIG. 24, shedding vortices  15  having a frequency indicative of the flow rate are produced. A transducer  26  of the vortex sensor assembly  11 , preferably located at the bluff body  24 , senses a pressure difference associated with the shedding vortices  15 . The vortex sensor  26  can include, for example, a piezoelectric sensor. The sensor  26  has characteristics approximated by a potential source E s  and a series capacitor C s . The magnitude of the output signal from the piezoelectric sensor  26  is proportional to the differential pressure, which is proportional to ρV 2 , where ρ is the fluid density and V is the velocity of the fluid  14 , and also proportional to ρD 2 F 2 , where D is the inside diameter of the meter housing  22  and F is the shedding frequency of the vortices  15 . 
     The output of the transducer  26  is coupled to an amplifier  28  which includes capacitor C F  and a resistor R F . The amplifier  28  provides an analog output signal on line  30 . The signal on line  30  is provided to input circuitry  60  including an anti-aliasing filter  62  and an analog-digital (sigma-delta) converter indicated at  64 . The anti-aliasing filter  62  filters the signal from line  30  to remove unwanted high-frequency noise and performs anti-aliasing filtering. 
     The analog-digital converter  64  samples the signal from filter  62  at approximately 307.2 kHz and outputs a single bit datastream at 307.2 kHz which is indicative of the amplitude and frequency of the vortices  15 . There are no word boundaries in the datastream. The relative number of ones and zeros, sometimes called the bit density, is representative of the signal on line  30 . The analog-digital converter  64 , which is preferably implemented in a CMOS ASIC to minimize power, cost, and size, is particularly suited to digitizing analog signals in the 1 to 10 kHz range, which is a typical frequency range for vortex flowmeters. The digital datastream is transmitted across an electrical isolation barrier  66  required for sensors which are grounded or have leakage current to ground. Such sensors are typically used in vortex flowmeters to reduce cost and simplify connections. The single bit datastream enables an inexpensive, compact transformer or capacitor to be used in the isolation barrier  66 . Other isolation media are acceptable such as optical, piezoelectric/acoustic and magnetostrictive isolation means. 
     The single bit datastream is provided through the isolation barrier  66  to a digital tracking filter  68 . The digital tracking filter  68  minimizes frequency quantization noise present in the analog-digital converter  64 , and also converts the amplitude and frequency vortex sensor signal on line  30  into a flowmeter output indicative of mass flow. The digital filter  68  receives a noise-contaminated input signal related to flow having a fundamental frequency varying responsively to flow. The digital filter  68  filters the input signal with high pass (HP) filter characteristics and preset low pass (LP) filters to produce a filtered signal representative of flow. The frequency characteristic of the HP filter is selected from a family of preselected HP filters having different corner frequencies. In a preferred embodiment, multiple HP filters are used. A microprocessor  70  selects appropriate corner frequencies of the digital filter  68  or suitable control is provided in the digital filter  68  to select the corner frequencies. The digital filter  68  provides a signal related to the amplitude of the signal on line  30  and, which is roughly proportional to the density, ρ V , of the fluid. The signal ρ V , in turn is used to calculate the mass flow rate M. The ρ V  signal is preferred over another signal ρV also available from the digital filter  68  because the digital filter  68  has removed more noise from the ρ V  signal. U.S. Pat. No. 5,429,001 assigned to the same assignee as the present application, and which is hereby incorporated by reference, describes in detail operation of the digital filter  68  to provide the ρ V  signal. U.S. Pat. No. 5,942,696 entitled “RAPID TRANSFER FUNCTION DETERMINATION FOR A TRACKING FILTER”, and which is also hereby incorporated by reference, discloses an alternative digital tracking filter. However, an error of approximately 5% compared to actual fluid density can exist in the ρ V  signal obtained from either of these digital tracking filters. This error is attributable to the fluid effects on the bluff body  24 . 
     In one aspect of the present invention, the vortex flowmeter  10  improves the accuracy of the output value indicative of flow rate, typically mass flow rate M, by monitoring additional parameters of the fluid  14  flowing in the conduit  16  and using the additional parameters to calculate the desired output value indicative of the flow rate. In the embodiment illustrated, the temperature and the pressure of the fluid  14  flowing in the conduit  16  are measured and provided as an input  80  to the microprocessor  70  The temperature is measured with a suitable temperature sensor  82  such as an RTD (resistive temperature device) or a thermocouple that senses a temperature of the fluid  14 , upstream or downstream from the bluff body  24 . In the embodiment illustrated, the temperature sensor  82  is disposed in a streamlined body  84  such as an airfoil for ruggedness and to minimize pressure drop along conduit  16 . A suitable pressure sensor  86  senses the line pressure of the fluid in the conduit  16 . The temperature sensor  82  and the pressure sensor  86  provide output signals to suitable analog-digital converters indicated at  64  (filtering can be provided if necessary). The analog-digital converters  64  transmit corresponding digital signals across the isolation barrier  66  to a decoder  88  that, in turn, provides the signal  80  to the microprocessor  70 . In the embodiment illustrated, both the temperature sensor  82  and the pressure sensor  86  are located downstream from the bluff body  24  to avoid disturbing the generation of vortices  15 . In a preferred embodiment, the temperature sensor  82  is located approximately six times the inside diameter of the meter housing  22  from the bluff body  24 , while the pressure sensor  86  is located approximately four times the inside diameter of the meter housing  22  from the bluff body  24 . At these locations, output values obtained from the temperature sensor  82  and the pressure sensor  86  have negligible errors and can be used to calculate fluid density ρ V . 
     FIG. 2 illustrates a flow chart depicting overall operation of the vortex flowmeter  10 . The flow chart begins at step  100 . From step  100 , program flow can be considered as operating along parallel paths indicated at  101  and  103 . In practice, the vortex flowmeter  10  executes operational steps in path  101  and performs successive iterations through path  101  before completing a single iteration through path  103 . Specifically, the microprocessor  70  will execute operational steps in path  103  in the “background” wherein these steps, or portions thereof, are completed when time is available during or at the completion of the operational steps of path  101 . As will be described below, the operational steps of path  101  provide, as a result, the desired output value indicative of flow, herein the mass flow rate M of the fluid  14  in the conduit  16 . However, during normal operation of the vortex flowmeter  10 , the accuracy of the calculated mass flow rate M is improved by correcting for temperature and pressure of the fluid  14  through the operational steps of path  103 . 
     Referring first to path  101 , at step  105 , the vortex flowmeter  10  obtains the frequency and amplitude data from the vortex sensor  11 , providing that data to the digital tracking filter  68  as described above. The digital tracking filter  68  then provides, at step  107 , the density ρ V , which is indicative of the flow of the fluid  14  in the conduit  16 . Calculations performed at step  107  include applying a stored scaling constant, β, to account for differences in the sensitivity of the vortex sensor  11  and electronics  12 , which can vary from element to element for a given line size, for example, ±30% from nominal. Preferably, β is adjusted such that ρ V  substantially corresponds to ρ G  or ρ L  from step  110  discussed below (i.e. C is approximately equal to one). The density value ρ V  is then used by the microprocessor  70  in accordance with known equations to calculate the mass flow rate M (similar to that described in U.S. Pat. No. 5,429,001) at step  109 . However, in this embodiment of the vortex flowmeter  10  of the present invention, the density value ρ V  is corrected with a calibration factor C that is calculated from the operational steps of path  103 . Since the calibration factor C can be dependent upon at least one value of the density ρ V , and since the calibration factor C may not have been calculated for the first iteration along path  101 , the calibration factor C can be initially set to one. 
     Referring now to path  103 , the microprocessor  70  reads at step  102  fluid parameters, such as temperature and pressure from line  80  and obtains a ρ V  that was calculated at  107  and that corresponds in time with the measured temperature and pressure. At this point, program flow will traverse subpaths  103 A,  103 B, or  103 C depending on whether the fluid is a gas or liquid, or whether little or any properties of the fluid is known. 
     If the fluid is a gas, program flow continues along path  103 A. At step  104 , the microprocessor  70  calculates a compressibility factor, Z, of the fluid  14  flowing in the conduit  16 . There are a number of standards for calculating compressibility factors which have been promulgated by a number of organizations such as the American Gas Association. FIGS. 3A and 3B are representative of the variation in the compressibility factor as a function of pressure at various temperatures for gasses having different constituents. Microprocessor  70  preferably calculates the compressibility factor using stored coefficients associated with a particular fluid. Since one set of coefficients is required for each of a plurality of fluids contemplated, and because the magnitude of the compressibility factor varies significantly, it is preferable to use polynomials of the form:          1   Z     =       ∑   i            ∑   j            A   ij                       P   i       T   j                                    
     where A ij  is a curve fitting derived constant stored in memory (EEPROM)  81 , T is the process absolute temperature and P is the absolute pressure, and where i and j preferably take on integer values between 0 and 9, depending on the accuracy required to calculate the compressibility factor. A 63 term polynomial (i=0 to 8, j=0 to 6) suffices for most applications. Polynomials of this form and number of terms reduce the amount of computation over direct calculation methods, thereby reducing the time between updates of the calibration factor C and the operating power requirements of vortex flowmeter  10 . Moreover, such a technique obviates a large memory to store many numbers of auxiliary constants, again saving power. 
     After the compressibility factor, Z, has been calculated at step  104 , this value is used at step  106  to calculate a density value ρ G  according to the ideal gas law. 
     If the fluid  14  is a liquid, after step  102 , program flow continues along a path  103 B. The path  103 B includes a step  108  where the density ρ L  for the liquid is calculated. The microprocessor  70  preferably calculates ρ L  using stored polynomials of the form:          ρ   L     =       ∑   k            ∑   l            B   kl                       P   k       T   l                                    
     where B kl  is a curve fitting derived constant stored in memory  81 , T is the process absolute temperature and P is the absolute pressure, and where k and l can take on appropriate integer values depending on desired accuracy. If desired, since liquids are substantially incompressible, the term P k  can be omitted. 
     A calibration factor, C, is calculated at step  110  as a function of ρ G  or ρ L  and Pρ V . The calibration factor, C, can be a simple ratio obtained from these values, or, in the alternative, can be a rolling average or a time weighted average. 
     Subpath  103 C represents calculation of a calibration factor C wherein little, if any, is known of the fluid properties of the fluid flowing through the conduit  16 . Generally, the calibration factor can be expressed as: 
     
       
         
           C=C 
           ref 
           +ΔC 
         
       
     
     where C ref  is an average value of the calibration factor and wherein ΔC is a small value calculated as a function of available parameters such as the pressure from the pressure sensor  86 , the temperature as measured from the temperature sensor  82 , ρ V  as calculated at step  107 , or any other known parameters of the fluid, for example, the dynamic viscosity. For instance, the microprocessor  70  can calculate a calibration factor for changes of the vortex sensor assembly  11  output in stiffness or elasticity as a function of pressure and temperature. In a further embodiment, the microprocessor  70  can calculate a Reynold&#39;s Number using ρ V , the velocity of the flowing fluid V (obtained from the shedding frequency), the diameter of the meter and the dynamic viscosity μ, which is a function of temperature and fluid type. Although calculation of the Reynold&#39;s Number requires knowing the dynamic viscosity of the fluid, an approximation can be used. The dynamic viscosity can simply be a constant (ignoring any temperature effects) or can also be as a function of temperature of the form:          1   μ     =       ∑   n                       D   n       T   n                                
     depending on the extent of knowledge of the fluid properties wherein D n  is curve fitting derived constant, T is the process absolute temperature and n can take on an appropriate integer value, depending on desired accuracy. Knowing the Reynold&#39;s Number, the microprocessor  70  can correct the “K Factor” and/or a coefficient of pressure on the bluff body  24  that determines differential pressure (ΔP=C P ρV 2 ). If desired, the microprocessor  70  calculates the calibration factor C using stored polynomials of the form:        C   =       ∑   r            ∑   s            C   rs                   Δ                   P   r        Δ                   T   s                                  
     where C rs  is a curve fitting derived constant stored in memory  81 , ΔT is the difference between the actual temperature from a reference temperature and ΔP is the difference between the actual pressure and a reference pressure, and where r and s can take on appropriate integer values, depending on desired accuracy. If desired, values for ρ V , μ, mach number or other known characteristics or measured fluid parameters can also be incorporated in this equation. 
     Once the calibration factor C has been calculated it is then used in step  109  for successive iterations of path  101  until a new calibration factor is again calculated in the background during the successive iterations. The microprocessor  70  provides the final output value to a digital-analog converter  83  for converting the digital value to a 4-20 mA current representative of the flow. A digital communications circuit  85  also can receive the final output value for transmission on the current loop  17  using known formats. If desired, a generator  87  can also receive the final output value of mass flow and through an isolator  89  provide a frequency output F out  from a pulse circuit  95 . Otherwise, the generator  87  can receive a signal  79  indicative of volumetric flow from the digital tracking filter  68 . The microprocessor  70  provides suitable scaling constants to the generator  87  when F out  is indicative of volumetric flow. A display  73  provides a user interface for the vortex flowmeter  10 . 
     In this manner, the single microprocessor  70  can be used for all processing thereby minimizing the power consumed by the vortex flowmeter  10 , allowing it to be completely powered from the current loop  17 . Although steps in path  103  require additional processor time, these calculations can be performed by the microprocessor  70 , while still providing the desired update rate for the mass flow rate M. This would not be possible if the microprocessor  70  had to calculate the mass flow signal M solely from the density value ρ L  or ρ G . Under those circumstances, either the update rate of the microprocessor  70  would have to be reduced to stay within available power limits from the current loop  17 , or additional power would have to be provided. In the preferred embodiment, the update rate is maintained without exceeding the available power budget because steps in path  103  are performed at a rate less than the update rate of the mass flow rate M. 
     FIG. 1A illustrates an exemplary embodiment having two microprocessors  70 A and  70 B. The microprocessor  70 A calculates the mass flow rate M pursuant to the flow chart of FIG. 2 as described above. The microprocessor  70 B communicates with the microprocessor  70 A through a data bus  71 . The microprocessor  70 B controls the generator  87  and the display  73 , and communicates over the current loop  17  with a remote location, not shown, through the digital-analog converter  83  and the digital communications circuit  85 . FIG. 1A illustrates one embodiment where multiple microprocessors  70 A and  70 B are used to perform operational tasks. Embodiments having more than two microprocessors, or where the operational tasks have been delegated differently are also within the scope of the present invention. 
     Another aspect of the present invention includes calculating additional corrections or providing alarms for volumetric as well as mass flow for both liquids and gasses using the measured pressure and/or temperature. For example, temperature compensation for the “K factor” (ratio of vortex shedding frequency to volumetric flow rate) due to thermal expansion of the meter housing  22  can be provided. As an example, if the meter housing  22  is made from stainless steel, temperature compensation for K factor due to thermal expansion is approximately 0.3% /100° F. Flowmeter  10  would store both a nominal K factor and a correction factor based on the thermal expansion coefficient and the measured temperature. The microprocessor  70  would then use both the nominal K factor and the correction factor to calculate output flow value. 
     Another correction includes calculation of pressure and temperature changes in viscosity of the fluid  14  to determine a Reynold&#39;s Number correction to the K factor. This correction is particularly useful for higher viscosity liquids flowing at low flow rates in small conduits. Hence, both a nominal Reynold&#39;s Number and a correction factor (based on temperature, pressure, and fluid type) would be stored and used by flowmeter  10 . 
     In yet another embodiment, an alarm is provided when incipient cavitation is present in the vortex sensor  11 . Incipient cavitation results when the pressure of the fluid  14  is near or below the vapor pressure of the fluid. The following equation represents the minimal allowable line pressure, P L , five diameters downstream from the meter  22 : 
     
       
         
           P 
           L 
           =AΔP+BP 
           VAP 
         
       
     
     where ΔP equals the upstream to downstream pressure drop across the bluff body  24  (Δρ=C X   ρV   2 , where C X  is a proportionability constant), A is a constant associated with a localized minimum pressure point on the bluff body  24 , P VAP  is the vapor pressure of the fluid  14  stored as an equation or as a table in memory  81 , and B is a constant indicating a threshold margin near the vapor pressure. For instance, constant A can have a value approximately equal to 2.9 (at five diameters downstream), while constant B can have a value approximately equal to 1.3. Constants A and B may vary depending on the actual location of the measured pressure. Preferably, the microprocessor  70  performs this calculation when the amplitude signal from vortex sensor  11  drops below expected values. If the microprocessor  70  calculates that the line pressure of fluid  14  is approaching the vapor pressure, an alarm can be provided over line  17  or at the display  73  indicating cavitation. Otherwise, an alarm can be provided indicating an error in the vortex flowmeter  10 . 
     In another embodiment, the microprocessor  70  uses the measured pressure and temperature data to calculate if condensation is occurring in the gasses flowing through the vortex flowmeter  10 . In such a situation, the microprocessor  70  can provide an alarm indicating operation in the gas condensation region. 
     In an embodiment for a steam application, the microprocessor  70  calculates the quality of steam by comparing the density value ρ G  from the measured pressure and temperature data to the density value ρ V  obtained from amplitude measurements. The microprocessor  70  provides a signal indicative of steam quality over the current loop  17  to the remote location. 
     In yet another embodiment, microprocessor  70  calculates the dynamic pressure on the bluff body  24  from the density ρ L  or ρ G  and the fluid flow rate, or such amplitude can be inferred from the output from sensor  11 . If the dynamic pressure exceeds a predetermined value dependent on a maximum allowable value beyond which fatigue and/or structural damage can occur to the bluff body  24  or the sensor  11 , the microprocessor  70  can provide an alarm signal on line  17 . 
     In a further embodiment, the microprocessor  70  compares the values of ρ V  with ρ L  or ρ G  and provides an alarm if a difference between these values exceeds a preselected threshold to indicate failure or degradation of sensor  11  or electronics  12 . In addition, the microprocessor  70  can monitor the signals obtained from the temperature sensor  82  and the pressure sensor  86  to ascertain if the signals are outside of usable ranges. If either of these signals are outside the usable range, the microprocessor  70  can stop calculating the calibration factor because values obtained may be in error. In this situation, the microprocessor  70  can provide an alarm indicating that mass flow is only being calculated via path  101  wherein the calibration factor C has been set to a default value such as one or the last usable value. Likewise, the microprocessor  70  can monitor the ρ V  signal from the digital filter  68  and calculate the mass flow based only values of ρ G  or ρ L  if the signal of ρ V  appears to be in error. The microprocessor  70  can provide a different alarm if the values ρ G  or ρ L  are only being used. 
     Each of the foregoing calculations would require additional processor time from the microprocessor  70  and may be accomplished only with a slower update rate on the calculated corrections and/or alarms because of the multi-tasking of the microprocessor  70 . Generally, these corrections are small and would not need updating faster than a 10 to 20 second rate. If desired, an integer multiply function can be provided in the ASIC to assist in these calculations, particularly if the update rates of the correction calculations exceed 20 to 30 seconds. Also, with the integer multiply function in the ASIC, the pressure and temperature values can be corrected for linearity, zero offsets and temperature offset compensation. 
     In another embodiment, data from the temperature sensor  82  and the pressure sensor  86  can be used to calibrate a new vortex sensor  11  in the event the vortex sensor  11  needs to be replaced. Specifically, if the vortex sensor  11  is replaced, the microprocessor  70  compares the value of ρ V  with either values from ρ G  or ρ L  and adjusts the scaling constant β in memory  81  that equates ρ G  or ρ L  to ρ V  so that C remains substantially equal to one. The microprocessor  70  has then calibrated the new vortex sensor  11  and operation continues pursuant to FIG.  2 . 
     In an alternative embodiment illustrated in FIGS. 4-7, the temperature sensor  82  and the pressure sensor  86  are mounted to the meter housing  22  between connecting flanges  22 A and  22 B. The temperature sensor  82  is mounted in the streamlined body  84  located upstream or downstream from the bluff body  24 . The streamlined body  84  is also illustrated in FIGS. 6-7 and includes an inner recess  102  for receiving the temperature sensor  82 , for example, a type-N thermocouple, mounted therein. The streamlined body  84  mounts to the meter housing  22  and extends through a recess  103 . Referring also back to FIG. 4, a signal line  104  connects the temperature sensor  82  to the electronics  12  located in a transmitter housing  106 . 
     In this embodiment, a support tube  108  supports the transmitter housing  106  on the meter housing  22 . The pressure sensor  86  is disposed in a connecting module  111  between the support tube  108  and the transmitter housing  106 . Fluid pressure is provided to the pressure sensor  86  through a passageway  110 A having at least one port  112  opening to the fluid  14  between the flanges  22 A and  22 B. In the embodiment illustrated, the ports  112  are located in the streamlined body  84 . The passageway  110  A includes an inner bore  113  and a tube  115 . Preferably, the tube  115  includes a loop  115 A for a condensation trap. A valve  117  is provided in the passageway  110 A to allow replacement of the pressure sensor  86  in the field. 
     In yet another embodiment illustrated in FIGS. 8 and 9, the temperature sensor  82  and the pressure sensor  86  are mounted to the meter housing  22  between connecting flanges  22 A and  22 B. The temperature sensor  82  is mounted in a streamlined body  184  located downstream from the bluff body  24 . The streamlined body  184  is also illustrated in FIG.  5  and includes an inner recess  186  for receiving the temperature sensor  82 , for example, a type-N thermocouple, mounted therein. Referring also back to FIG. 8, a signal line  188  connects the temperature sensor  82  to the electronics  12  located in a transmitter housing  190 . 
     In this embodiment, a support tube  192  supports the transmitter housing  190  on the meter housing  22 . The pressure sensor  86  is disposed in the transmitter housing  190 . Fluid pressure is provided to the pressure sensor  86  through a passageway  194  having a port  196  through the meter housing  22  and opening to the fluid  14  between the flanges  22 A and  22 B. In the embodiment illustrated, the pressure port  196  is positioned proximate the bluff body  24 , in the embodiment illustrated upstream thereof. 
     In the foregoing embodiments, the streamlined bodies  84  and  184  are oriented substantially parallel to the bluff body  24 . FIGS. 10 and 11 illustrate another orientation of the streamlined body  184 . The streamlined body  184  is oriented such that a longitudinal axis  184 A of the streamlined body  184  is non-parallel to a longitudinal axis  24 A of the bluff body  24 . Non-parallel orientation minimizes forces from the shedding vortices exerted upon the streamlined body  184 . The axis  184 A is oriented substantially orthogonal to the axis  24 A; however, as appreciated by those skilled in the art, other non-parallel orientations can be used. For instance, other embodiments can include orienting the axis  184 A relative to the axis  24 A to form an acute angle  193  between the axes  184 A and  24 A. In a further embodiment, the acute angle  193  is in the approximate range of 30 degrees to less than 90 degrees. 
     It should also be noted that the streamlined body  184  need not be disposed on the diameter of the flowtube  16  (as illustrated) but rather, can be disposed off the diameter of the flowtube  16  as illustrated by dashed lines  195 A and  195 B by way of example. In addition, one streamlined body design may be used in flowtubes of varying diameters so as to minimize manufacturing costs. Generally, the streamlined body  184  is of sufficient length to dispose the temperature sensor  82  at an immersion depth suitable to obtain an accurate temperature measurement within allowable tolerances. As appreciated by those skilled in the art, the immersion depth is further related to the velocity and density of the fluid and the heat transfer capabilities of the fluid, streamlined body  184  and flowtube  22 . 
     As stated above, the temperature sensor  82  can be disposed upstream from the bluff body  24 . FIG. 10 illustrates location of a streamlined body  197  and temperature sensor  82  upstream of the bluff body  24 . Upstream location of the temperature sensor  82  can realize a more compact structure in view that the measurement of fluid temperature in the shedding vortices is generally inaccurate. The streamlined body  197  is substantially similar to the streamlined body  184 . As described above with respect to the streamlined body  184 , the streamlined body  197  can be disposed in a non-parallel orientation with respect to the bluff body  24 . In this manner, potential disturbances of fluid flow are minimized. 
     The location of ports  112  and temperature sensor  82  in FIGS. 4-7 and  10 - 11 , the port  196  and temperature sensor  82  in FIGS. 8 and 9, and other convenient locations in the meter housing  22  for obtaining the temperature and pressure of the fluid can include corrections due to the dynamic pressure head (proportional to ρV 2 ) and temperature recovery factor: 
     
       
         Δ T=rV   2 /2 C   S   
       
     
     where C S  is the specific heat at constant pressure and r is a recovery factor). The microprocessor  70  uses the measured pressure and temperature in the meter housing  22 , the measured density ρ V  and calculated density ρ G  or ρ L , in appropriate thermodynamic, energy and momentum equations to correct for errors due to measurement locations. For instance, pressure in front of the bluff body  24  is related to the pressure at four diameters downstream from the bluff body  24  by the following equation: 
     
       
         
           P−P 
           4D 
           =C 
           P 
           ρV 
           2 
         
       
     
     where P is the pressure ahead of the bluff body  24 , P 4D  is the pressure four diameters downstream from the bluff body  24 , C P  is a pressure loss coefficient that varies with Reynold&#39;s Number, ρ is the density of the fluid and V is the velocity of the fluid. Measurement locations between the mounting flanges  22 A can provide better mechanical arrangements for the meter housing  22 , less sensitivity to location errors, less conduction errors on the temperature sensor, reduced interference with vortex shedding frequency, and reduced plugging of pressure ports. In this manner, the vortex flowmeter  10  can be assembled entirely at the factory, reducing the overall size and cost of the flowmeter  10 , and making installation easier since additional penetration points in the conduit are not needed. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.