Multi-measurement vortex flowmeter

Abstract

Two-wire transmitters are described in which the required voltage that a control room must supply to the transmitter is lower at high current than at low current, thus freeing up more voltage for other uses, and in which a constant set of operating voltages may be maintained. A corrected pressure in a vortex flow meter may be determined that reflects the mass flow rate. Thus, the mass flow rate may be determined based on the corrected pressure reading and a measured volumetric flow rate. Density may be determined from pressure and temperature using a table containing error values based on a standard density determination and a relatively simple approximation. During operation of a flow meter, the stored error values may be linearly interpolated and the approximation may be computed to determine the density from the stored error value.

1 . A computer-implemented method of specifying a transmitter, the transmitter for regulating an amplitude of a supplied current to encode a parameter, the method comprising providing a set of data to a customer, wherein the set of data represents a maximum allowable load at one or more supply voltage levels, and the set of data has a first segment operable only for a lower range of currents below a transition current and has a second segment operable only for a higher range of currents above the transition current. 
     
     
         2 . The method of  claim 1  wherein:
 the first segment results from the transmitter multiplying a regulated current by a first non-unitary factor when the regulated current is within the lower range of currents, and 
 the second segment results from the transmitter multiplying the regulated current by a second non-unitary factor when the regulated current is within the higher range of currents. 
 
     
     
         3 . The method of  claim 2  wherein the first segment approximates a first line having a first slope, the second segment approximates a second line having a second slope, and the first slope is at least twice as large as the second slope. 
     
     
         4 . A method of controlling a current signal, the method comprising:
 receiving a current with a variable amplitude over a line, the amplitude being regulated;   multiplying the regulated amplitude by a first non-unitary factor when the regulated amplitude is below a first level;   multiplying the regulated amplitude by a second non-unitary factor when the regulated amplitude is above a second level;   maintaining a constant set of operating voltages whether the regulated amplitude is multiplied by the first non-unitary factor or the second non-unitary factor; and   providing the multiplied amplitude and the constant set of operating voltages to circuitry.   
     
     
         5 . The method of  claim 4  wherein:
 receiving the variable current comprises receiving the current at a transmitter, and 
 the amplitude is regulated by the transmitter to communicate an output parameter by encoding a value of the output parameter on the current. 
 
     
     
         6 . The method of  claim 4  wherein maintaining a constant set of operating voltages comprises using a reversible power transformation. 
     
     
         7 . The method of  claim 6  wherein:
 multiplying by the first non-unitary factor comprises injecting the regulated current into an input of a first multiplier and coupling an output of the first multiplier to an input of a second multiplier, 
 multiplying by the second non-unitary factor comprises injecting the regulated current into the input of the second multiplier and into the output of the first multiplier, and 
 maintaining the constant set of operating voltages comprises using a reversible multiplier for the first multiplier, allowing regulated current that is coupled to the output of the first multiplier to produce a current emanating from the input to the first multiplier and having an amplitude approximately equal to the regulated current divided by the first non-unitary factor. 
 
     
     
         8 . The method of  claim 7  wherein maintaining the constant set of operating voltages further comprises regulating a voltage at the input of the first multiplier, providing the same voltage whether the regulated current is injected into the input of the first multiplier or the input of the second multiplier. 
     
     
         9 . The method of  claim 4  wherein the transmitter receives power from a supply over the line. 
     
     
         10 . The method of  claim 9  wherein the regulated current extends over a range of about 4 milliamps to 20 milliamps. 
     
     
         11 . The method of  claim 5  wherein the output parameter is a vortex frequency, a linear flow rate, or a volumetric flow rate. 
     
     
         12 . The method of  claim 4  wherein:
 receiving the variable current comprises receiving the current at a transmitter, and 
 the amplitude is regulated before being received by the transmitter. 
 
     
     
         13 . A transmitter comprising:
 a switching circuit configured to couple a regulated current to either a first output or a second output based on an amplitude of the regulated current;   a first non-unitary current multiplier having an input and an output, with the input of the first non-unitary multiplier being coupled to the first output of the switching circuit, the first non-unitary multiplier operable in a forward direction as a current multiplier and in a backward direction as a current divider; and   a second non-unitary multiplier having an input and an output, with the input of the second non-unitary multiplier coupled to both the second output of the switching circuit and the output of the first non-unitary multiplier.   
     
     
         14 . The transmitter of  claim 13  further comprising a current regulator coupled to an input of the switching circuit and configured to regulate the amplitude of the current to encode a value of an output parameter on the current. 
     
     
         15 . The transmitter of  claim 14  wherein the current regulator is configured to receive the current over a line in a two-wire system. 
     
     
         16 . The transmitter of  claim 15  wherein the current regulator is configured to regulate the amplitude over a range extending at least from 4 milliamps to 20 milliamps. 
     
     
         17 . The transmitter of  claim 14  wherein the current regulator is configured as part of a vortex flow meter system and is configured to encode a value of a vortex frequency, a linear flow rate, or a volumetric flow rate. 
     
     
         18 . A transmitter comprising:
 switching means, having a first output and a second output, for coupling a regulated current to either the first output or the second output based on an amplitude of the regulated current;   first means for multiplying current by a non-unitary number, the first means having an input and an output, with the input of the first means being coupled to the first output of the switching means, the first means being operable in a forward direction as a current multiplier and in a backward direction as a current divider; and   second means for multiplying current by a non-unitary number, the second means having an input and an output, with the input of the second means being coupled to both the second output of the switching means and the output of the first means.   
     
     
         19 . The transmitter of  claim 18  further comprising regulating means coupled to the switching means for regulating the amplitude of the current to encode a value of an output parameter on the current. 
     
     
         20 . A computer-implemented method of controlling a current signal, the method comprising:
 receiving a current with a variable amplitude over a line, the amplitude being regulated;   multiplying the regulated amplitude by a first non-unitary factor when the regulated amplitude is below a first level;   multiplying the regulated amplitude by a second non-unitary factor when the regulated amplitude is above a second level;   maintaining a constant set of operating voltages whether the regulated amplitude is multiplied by the first non-unitary factor or the second non-unitary factor; and   providing the multiplied amplitude and the constant set of operating voltages to circuitry.