Multi-measurement vortex flowmeter
View Patent ↗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 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.
2. The transmitter of claim 1 further comprising a current regulator coupled to an input of the switching circuit and configured to regulate the amplitude of the regulated current to encode a value of an output parameter on the regulated current.
3. The transmitter of claim 2 wherein the current regulator is configured to receive an input current over a line in a two-wire system.
4. The transmitter of claim 3 wherein the current regulator is configured to regulate the amplitude over a range extending at least from 4 milliamps to 20 milliamps.
5. The transmitter of claim 2 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.
6. The transmitter of claim 1 wherein the first and second non-unitary current multipliers each comprises a voltage divider.
7. A method comprising:
coupling, by a switching circuit having a first output and a second output, a regulated current to either the first output or the second output based on an amplitude of the regulated current;
multiplying, by a first multiplier, current by a non-unitary number, wherein the first multiplier has an input and an output and the input of the first multiplier is coupled to the first output of the switching circuit, and wherein the first multiplier is operable in a forward direction as a current multiplier and in a backward direction as a current divider; and
multiplying, by a second multiplier, current by a non-unitary number, wherein the second multiplier has an input and an output and the input of the second multiplier is coupled to both the second output of the switching circuit and the output of the first multiplier.
8. The method of claim 7 further comprising regulating the amplitude of the regulated current to encode a value of an output parameter on the regulated current.
9. The method of claim 8 wherein regulating the amplitude of the regulated current comprises receiving an input current over a line in a two-wire system.
10. The method of claim 8 wherein regulating the amplitude of the regulated current comprises regulating the amplitude over a range extending at least from 4milliamps to 20 milliamps.
11. The method of claim 8 wherein regulating the amplitude of the regulated current comprises encoding a value of a vortex frequency, a linear flow rate, or a volumetric flow rate as part of a vortex flow meter system.
12. The method of claim 7 wherein the first and second multipliers each comprises a voltage divider.