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Description  |
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FIELD OF THE INVENTION
This invention relates to electronic components for controlling power drawn
by a measurement device.
PROBLEM
It is known to use Coriolis effect mass flowmeters to measure mass flow and
other information for materials flowing through a conduit in the
flowmeter. Exemplary Coriolis flowmeters are disclosed in U.S. Pat. No.
4,109,524 of Aug. 29, 1978, U.S. Pat. No. 4,491,025 of Jan. 1, 1985, and
U.S. Pat. No. Re. 31,450 of Feb. 11, 1982, all to J. E. Smith et al. These
flowmeters have one or more conduits of straight or curved configuration.
Each conduit configuration in a Coriolis mass flowmeter has a set of
natural vibration modes, which may be of a simple bending, torsional or
coupled type. Each conduit is driven to oscillate at resonance in one of
these natural modes. Material flows into the flowmeter from a connected
pipeline on the inlet side of the flowmeter, is directed through the
conduit or conduits, and exits the flowmeter through the outlet side of
the flowmeter. The natural vibration modes of the vibrating, material
filled system are defined in part by the combined mass of the conduits and
the material flowing within the conduits.
When there is no flow through the flowmeter, all points along the conduit
oscillate due to an applied driver force with identical phase or small
initial fixed phase offset which can be corrected. As material begins to
flow, Coriolis forces cause each point along the conduit to have a
different phase. The phase on the inlet side of the conduit lags the
driver, while the phase-on the outlet side of the conduit leads the
driver. Pick-off sensors on the conduit(s) produce sinusoidal signals
representative of the motion of the conduit(s). Signals output from the
pick-off sensors are processed to determine the phase difference between
the pick-off sensors. The phase difference between two pick-off sensor
signals is proportional to the mass flow rate of material through the
conduit(s).
Materials flowing through the Coriolis flowmeter can be hazardous
materials. In order to safeguard the flow of hazardous materials, there
are requirements for environmental seals and hazardous area approvals. One
set of requirements are Intrinsically Safe (IS) requirements which
minimize risks for an electric spark that could ignite explosive gases.
Therefore, designs of measurement devices that comply with IS requirements
must account for a reduced amount of power provided to the measurement
device.
In one prior Coriolis flowmeter, a power supply is connected to an IS
barrier. The IS barrier limits the current and voltage provided to the
Coriolis flowmeter. The IS barrier is connected to a sensor of the
Coriolis flowmeter via a power link. One problem relates to a lead
resistance of the power link. The length of the power link varies
depending on how far the power supply and the IS barrier are from the
sensor in the hazardous area. Increasing the length of the power link
increases the lead resistance of the power link. Thus, the increased
resistance of the power link reduces the power available to the
transmitter and the sensor.
Another problem with the increased resistance of the power link is a
resetting problem. The resetting problem occurs when too much resistance
exists in the power link. When power is initially applied to the
electronics part of the flowmeter, current flow through the power link is
relatively low, because the electronics have not yet begun to apply power
in turn to the mechanical sensor. As the electronics begins to apply power
to the sensor, current flow through the power link may increase enough to
decrease the input voltage to the electronics to a threshold where the
electronics goes into reset, and all power draw ceases. The cycle may then
repeat.
One solution for this resetting problem is a worst case usage solution. A
worst case usage of current is calculated from an assumption of a worst
case sensor. The maximum lead resistance is then calculated from the worst
case usage of current. The maximum lead resistance limits the maximum
length of the power link. However, many sensors operate normally on much
less current than the worst case sensor. For example, one low power sensor
operates on one tenth the current of the worst case sensor. This low power
sensor could support a longer power link with more resistance than the
worst case sensor. Another option of larger gauge wires, which have a
lower resistance per unit distance, also do not solve the above problems
due to the UR ratio of the larger gauge wires.
SOLUTION
The invention solves the above problems and other problems by controlling
the power drawn by a measurement device. The measurement device measures a
first voltage across the measurement device. The measurement device then
determines an operating current based on the first voltage. The operating
current is a maximum current that the measurement device draws without
dropping a measurement device voltage below a threshold voltage to prevent
resetting of the measurement device. The measurement device then generates
a signal to change the power to use the operating current.
The measurement device using this invention determines an operating current
that is higher than the current for a measurement device that assumes a
worst case sensor. Thus, the measurement device advantageously has more
power available than the measurement device that assumes a worst case
sensor. The power available is maximized for any type of sensor in the
measurement device. Another advantage is the measurement device prevents
resetting for a measurement device with a large lead resistance in the
power link. Previously, the measurement device with a large lead
resistance resets. Also, the measurement device supports a longer length
of the power link than the measurement device that assumes a worst case
sensor.
One aspect of the invention is a measurement device for controlling power
drawn by the measurement device where the measurement device comprises a
transmitter configured to measure a first voltage across the measurement
device, determine an operating current based on the first voltage wherein
the operating current is a maximum current that the measurement device
draws without dropping a measurement device voltage below a threshold
voltage to prevent resetting of the measurement device, and generate a
signal to change the power to use the operating current, and a sensor
connected to the transmitter and configured to draw the operating current.
Another aspect of the invention is where the transmitter is configured to
apply a minimum quiescent current to the measurement device and measure
the first voltage across the measurement device occurs in response to
applying the minimum quiescent current.
Another aspect of the invention is where the measurement device is
configured to determine a lead resistance of the measurement device and
determine the operating current based on the lead resistance.
Another aspect of the invention is where the transmitter is configured to
receive and process the signal to change a variable resistance to change
the power.
Another aspect of the invention is where the transmitter is configured to
increase a first current of the measurement device, measure a second
voltage across the measurement device, determine a linear relationship of
current and voltage based on the first voltage, the second voltage, and
the increase in the first current, and determine the operating current
based on the linear relationship and a minimum voltage to prevent
resetting.
Another aspect of the invention is where the measurement device is a
Coriolis flowmeter.
Another aspect of the invention is a method for controlling power drawn by
a measurement device where the method comprises the steps of measuring a
first voltage across the measurement device, determining an operating
current based on the first voltage wherein the operating current is a
maximum current that the measurement device draws without dropping a
measurement device voltage below a threshold voltage to prevent resetting
of the measurement device, and generating a signal to change the power to
use the operating current.
Another aspect of the invention is a software product for controlling power
for a measurement device where the software product comprises (1)
transmitter software configured when executed by a processor to direct the
processor to measure a first voltage across the measurement device,
determine an operating current based on the first voltage wherein the
operating current is a maximum current that the measurement device draws
without dropping a measurement device voltage below a threshold voltage to
prevent resetting of the measurement device, and generate a signal to
change the power to use the operating current and (2) a software storage
medium operational to store the transmitter software.
DESCRIPTION OF THE DRAWINGS
The present invention can be understood from the following detailed
description and the following drawings:
FIG. 1 illustrates a Coriolis flowmeter in the prior art;
FlG. 2 illustrates a block diagram of a power supply and a measurement
device in an example of the invention;
FIG. 3 illustrates a block diagram of a Coriolis flowmeter device and a
power supply in an example of the invention;
FIG. 4 illustrates a block diagram of a transmitter of a Coriolis flowmeter
device in an example of the invention;
FIG. 5 illustrates a flowchart of a transmitter for calculating lead
resistance in an example of the invention;
FIG. 6 illustrates a flowchart for a transmitter for determining a linear
relationship of voltage and current in an example of the invention; and
FIG. 7 illustrates a graph of current vs. voltage in an example of the
invention.
DETAILED DESCRIPTION
FIG. 1 depicts an exemplary Coriolis flowmeter in the prior art. Coriolis
flowmeter 100 includes a flowmeter assembly 110 and meter electronics 150.
Meter electronics 150 are connected to a meter assembly 110 via leads 120
to provide for example, but not limited to, density, mass-flow-rate,
volume-flow-rate, and totalized mass-flow rate information over a path
125. A Coriolis flowmeter structure is described although it should be
apparent to those skilled in the art that the present invention could be
practiced in conjunction with any apparatus having loads require currents
of alternating voltage.
A Coriolis flowmeter structure is described although it should be apparent
to those skilled in the art that the present invention could be practiced
in conjunction with any apparatus having a vibrating conduit to measure
properties of material flowing through the conduit. A second example of
such an apparatus is a vibrating tube densitometer which does not have the
additional measurement capability provided by a Coriolis mass flowmeters.
Meter assembly 110 includes a pair of flanges 101 and 101', manifold 102
and conduits 103A and 103B. Driver 104, pick-off sensors 105 and 105', and
temperature sensor 107 are connected to conduits 103A and 103B. Brace bars
106 and 106' serve to define the axis W and W' about which each conduit
oscillates.
When Coriolis flowmeter 100 is inserted into a pipeline system (not shown)
which carries the process material that is being measured, material enters
flowmeter assembly 110 through flange 101, passes through manifold 102
where the material is directed to enter conduits 103A and 103B. The
material then flows through conduits 103A and 103B and back into manifold
102 from where it exits meter assembly 110 through flange 101'.
Conduits 103A and 103B are selected and appropriately mounted to the
manifold 102 so as to have substantially the same mass distribution,
moments of inertia and elastic modules about bending axes W--W and W'--W',
respectively. The conduits 103A-103B extend outwardly from the manifold in
an essentially parallel fashion.
Conduits 103A-103B are driven by driver 104 in opposite directions about
their respective bending axes W and W' and at what is termed the first out
of phase bending mode of the flowmeter. Driver 104 may comprise any one of
many well known arrangements, such as a magnet mounted to conduit 103A and
an opposing coil mounted to conduit 103B and through which an alternating
current is passed for vibrating both conduits. A suitable drive signal is
applied by meter electronics 150 to driver 104 via path 112.
Pick-off sensors 105 and 105' are affixed to at least one of conduits 103A
and 103B on opposing ends of the conduit to measure oscillation of the
conduits. As the conduit 103A-103B vibrates, pick-off sensors 105-105'
generate a first pick-off signal and a second pick-off signal. The first
and second pick-off signals are applied to paths 111 and 111'. The driver
velocity signal is applied to path 112.
Temperature sensor 107 is affixed to at least one conduit 103A and/or 103B.
Temperature sensor 107 measures the temperature of the conduit in order to
modify equations for the temperature of the system. Path 111" carries
temperature signals from temperature sensor 107 to meter electronics 150.
Meter electronics 150 receives the first and second pick-off signals
appearing on paths 111 and 111', respectively. Meter electronics 150
processes the first and second velocity signals to compute the mass flow
rate, the density, or other property of the material passing through
flowmeter assembly 110. This computed information is applied by meter
electronics 150 over path 125 to a utilization means (not shown).
It is known to those skilled in the art that Coriolis flowmeter 100 is
quite similar in structure to a vibrating tube densitometer. Vibrating
tube densitometers also utilize a vibrating tube through which fluid flows
or, in the case of a sample-type densitometer, within which fluid is held.
Vibrating tube densitometers also employ a drive system for exciting the
conduit to vibrate. Vibrating tube densitometers typically utilize only
single feedback signal since a density measurement requires only the
measurement of frequency and a phase measurement is not necessary. The
descriptions of the present invention herein apply equally to vibrating
tube densitometers.
In Coriolis flowmeter 100, the meter electronics 150 are physically divided
into 2 components a host system 170 and a signal conditioner 160. In
conventional meter electronics, these components are housed in one unit.
Signal conditioner 160 includes drive circuitry 163 and pick-off
conditioning circuitry 161. One skilled in the art will recognize that in
actuality drive circuitry 163 and pick-off conditioning circuitry 161 may
be separate analog circuits or may be separate functions provided by a
digital signal processor or other digital components. Drive circuitry 163
generates a drive signal and applies an alternating drive current to
driver 104 via path 112 of path 120. The circuitry of the present
invention may be included in drive circuitry 163 to provide an alternating
current to driver 104.
In actuality, path 112 is a first and a second lead. Drive circuitry 163 is
communicatively connected to pick-off signal conditioning circuitry 161
via path 162. Path 162 allows drive circuitry to monitor the incoming
pick-off signals to adjust the drive signal. Power to operate drive
circuitry 163 and pick-off signal conditioning circuitry 161 is supplied
from host system 170 via a first wire 173 and a second wire 174. First
wire 173 and second wire 174 may be a part of a conventional 2-wire,
4-wire cable, or a portion of a multi-pair cable.
Pick-off signal conditioning circuitry 161 receives input signals from
first pick-off 105, second pick-off 105', and temperature sensor 107 via
paths 111, 111' and 111". Pick-off circuitry 161 determines the frequency
of the pick-off signals and may also determine properties of a material
flowing through conduits 103A-103B. After the frequency of the input
signals from pick-off sensors 105-105' and properties of the material are
determined, parameter signals carrying this information are generated and
transmitted to a secondary processing unit 171 in host system 170 via path
176. In a preferred embodiment, path 176 includes 2 leads. However, one
skilled in the art will recognize that path 176 may be carried over first
wire 173 and second wire 174 or over any other number of wires.
Host system 170 includes a power supply 172 and processing system 171.
Power supply 172 receives electricity from a source and converts the
received electricity to the proper power needed by the system. Processing
system 171 receives the parameter signals from pick-off signal
conditioning circuitry 161 and then may perform processes needed to
provide properties of the material flowing through conduits 103A-103B
needed by a user. Such properties may include but are not limited to
density, mass flow rate, and volumetric flow rate.
The present invention is described more fully hereinafter with reference to
the accompanying drawings, in which embodiments of the invention are
shown. For instance, meter electronics 150 could be mounted integrally to
flowmeter assembly 110. Those skilled in the art will appreciate that the
invention may be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein; rather, these
embodiments are provided so that this disclosure is thorough and complete,
and fully conveys the scope of the invention to those skilled in the art.
In the drawings, like numbers refer to like elements throughout.
Measurement Device--FIG. 2
FIG. 2 depicts a block diagram of a power supply 210 and a measurement
device 220 in an example of the invention. The power supply 210 is
connected to the measurement device 220 via a power link 212.
The power supply 210 could be any power supply configured to provide power
to the measurement device 220 via the power link 212. The measurement
device 220 could be any device for measuring configured to (1) measure a
first voltage across the measurement device 220, (2) determine an
operating current based on the first voltage, and (3) generate a signal to
change the power to use the operating current. The operating current is a
maximum current that the measurement device 220 draws without dropping a
measurement device voltage below a threshold voltage to prevent resetting
of the measurement device 220. One example of the measurement device 220
is a Coriolis flowmeter device as described below in FIG. 3.
Resetting is when the measurement device 220 is powered off and then
detects enough voltage to turn on. When the measurement device 220 is
powered on, the current increases enough to decrease the terminal voltage
to a point where the measurement device 220 powers off.
In operation, the power supply 210 provides power to the measurement device
220 via the power link 212. The measurement device 220 measures a first
voltage across the measurement device 220. The measurement device 220 then
determines an operating current based on the first voltage. The
measurement device 220 then generates a signal to change the power to use
the operating current.
Coriolis Flowmeter Device--Intrinsically Safe--FIGS. 3-5
FIG. 3 illustrates a block diagram of a Coriolis flowmeter device 320 and a
power supply 310 in an example of the invention. The Coriolis flowmeter
device 320 includes an Intrinsically Safe (IS) barrier 330, a power link
340 with a lead resistance, a transmitter 350, and a sensor 360. The
transmitter 350 drives the sensor 360 with drive signals via a drive link
352. The sensor 360 is an electromechanical device attached to the
Coriolis flow tube. As material flows through the flow tube, the
transmitter 350 receives resultant signals from the sensor 360 via a
pick-off link 354. The mass flow, density, and temperature are then
derived from the resultant signals.
FIG. 4 depicts a block diagram of a transmitter 350 of a Coriolis flowmeter
device 320 in an example of the invention. The transmitter 350 includes a
Read Only Memory (ROM) 410, a Random Access Memory (RAM) 420, a processor
430, a Digital to Analog (D/A) converter 440, and an Analog to Digital
(A/D) converter 450. The ROM 410 is connected to the processor 430 via a
ROM link 412. The RAM 420 is also connected to the processor 430 via a RAM
link 422. The processor 430 is connected to the power link 340. The
processor 430 is connected to the D/A converter 440 via a drive link 442
and is connected to the A/D converter 450 via a pick-off link 452. The D/A
converter 440 is connected to the drive link 352. The A/D converter 450 is
connected to the pick-off link 354. In other embodiments, there may be
numerous pick-off links and A/D converters to receive signals from the
sensor 360 but are not discussed here for the sake of simplicity.
FIG. 5 depicts a flowchart of the transmitter 450 for calculating lead
resistance in an example of the invention. FIG. 5 begins in step 500. In
step 502, the processor 430 measures the voltage across the power link 340
when a minimum quiescent current is applied. There are numerous places
where the voltage could be measured across the transmitter 350 to
eventually determine the operating current. Some examples are the power
link 340 and the IS barrier 330. The minimum quiescent current is the
minimum current to turn on the drive circuitry of the sensor 360. In step
504, the processor 430 then determines the lead resistance of the power
link 340 using Ohm's law, the minimum quiescent current, and the voltage
measured in step 502. In step 506, the processor 430 determines the
operating current based on the lead resistance, the resistance of the
sensor 360, and the voltage of the power supply 310. The processor 430
then generates and transmits a signal to change the power to use the
operating current in step 508. In one embodiment, the signal may alter a
variable resistance, whether passive or solid-state, to change the power
to use the operating current. In an alternative embodiment, the power
supply 310 receives and processes the signal to change the power to use
the operating current. FIG. 5 ends in step 510.
Coriolis Flowmeter Device--Non-Intrinsically Safe--FIGS. 3, 4, and 6-7
In one non-intrinsically safe embodiment of the invention, the Coriolis
flowmeter device 320 in FIG. 3 does not include the IS barrier 330. FIG. 6
depicts a flowchart for the transmitter 350 for a linear relationship of
voltage and current in an example of the invention. FIG. 7 depicts a graph
of current vs. voltage in an example of the invention. FIG. 6 begins in
step 600. In step 602, the processor 430 measures a first voltage 702 at
the pick-off link 452. The processor 430 then generates and transmits an
increase signal to increase the current in step 604. The processor 430
then measures a second voltage 704 in step 606.
In step 608, the processor 430 then determines a linear relationship 710 of
current and voltage based on the increase in current, the first voltage
702, and the second voltage 704. In step 610, the processor 430 determines
the operating current 708 based on the linear relationship 710 and the
minimum voltage 706 to prevent resetting. The processor 430 then generates
and transmits a signal to change the power to use the operating current in
step 612. FIG. 6 ends in step 614.
The above-described elements can be comprised of instructions that are
stored on storage media. The instructions can be retrieved and executed by
a processor. Some examples of instructions are software, program code, and
firmware. Some examples of storage media are memory devices, tape, disks,
integrated circuits, and servers. The instructions are operational when
executed by the processor to direct the processor to operate in accord
with the invention. Those skilled in the art are familiar with
instructions, processor, and storage media.
Those skilled in the art will appreciate variations of the above-described
embodiments that fall within the scope of the invention. As a result, the
invention is not limited to the specific examples and illustrations
discussed above, but only by the following claims and their equivalents.
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