An analog flow meter instrument includes a flow meter monitoring
the flow of fluid. A sensor unit is secured to the flow meter and
include an indicator rod in an oil filled tube. The rod extends
into the flow meter and is positioned in accordance with the flow.
The sensor includes a housing having a slot to visually read the
location of the rod. A light beam unit is mounted to one side of
the tube and a plurality of phototransistors in a linear array are
mounted to the opposite side of the tube. The phototransistors are
connected in a current summing network to generate an analog current
signal, the amplitude of which is linearly related to the fluid
flow. The output signal is amplified and connected to output devices.
The analog signal can be reliably transmitted over relatively long
distances within the factory environment using conventional low
voltage wiring. A "dirty" oil monitor is connected to
the zero flow phototransistor and includes an LED which is energized
at zero flow and with flow if the dirty oil blocks proper light
1. A linear analog flow meter apparatus, comprising a transparent
sight glass tube coupled to a movable indicator unit positioned
within said sight glass tube in accordance with the flow, a housing
coupled to said sight glass tube and establishing a substantial
light enclosure, a light bank secured within said housing and establishing
a light beam aligned with and passing through said tube, a plurality
of individual light sensitive elements arranged in a bar fashion
to the opposite side of said tube and operable to establish a current
flow in response to engagement by said light beam, and a summing
circuit means connected to said light sensitive elements and summing
the output current flow of said elements and establishing a current
signal linearly proportional to the position of the indicator in
2. The analog flow meter apparatus of claim 1 including an amplifying
means connected to said summing circuit means for amplifying said
3. The apparatus of claim 2 wherein said amplifying means establishes
a floating D.C. current signal including a positive output signal
line and a negative output signal line.
4. The apparatus of claim 3 having an adjustable potentiometer
means for adjusting the output range of said D.C. current signal.
5. The apparatus of claim 1 including a visual readout coupled
to said indicator unit and operable to provide a continuous visual
readout of the flow.
6. The apparatus of claim 1 wherein said tube is filled with a
light transparent oil, said oil being subject to foreign matter
to reduce the transparency to said light beam, said elements being
spaced to define a minimum flow element at one end and a maximum
flow element at the opposite end, and an oil monitor unit connected
to one of said light sensitive elements spaced from said minimum
flow element and establishing a dirty oil output in response to
the present of a selected level of foreign material in the oil aligned
with said connected element.
7. The apparatus of claim 6 wherein said oil monitor unit is connected
to the element immediately adjacent said minimum flow element.
8. A linear analog flow meter instrument, comprising a float rod
assembly moving within a passageway through which fluid flows for
positioning in accordance with the rate of flow of fluid therethrough,
a transparent sight glass tube coupled to said passageway, said
rod assembly extending into said glass tube and having a movable
indicator within said sight glass tube, a light transparent oil
filling said tube, a housing coupled to said sight glass tube and
establishing a substantial light enclosure, a light bar within said
housing aligned with the sight glass tube and establishing a light
beam passing through said sight glass tube, a plurality of individual
phototransistors arranged in alignment in a bar fashion within said
housing and aligned with the light beam to the opposite side of
said sight glass tube, and a resistive summing network coupled to
sum the output of each of said phototransistors and establishing
a current signal linearly proportional to the position of the indicator
in said sight glass tube.
9. The apparatus of claim 8 having adjustable means for setting
the range of the flow rate.
10. The linear analog flow meter instrument of claim 8 wherein
said light bar includes a plurality of LED diode lamps arranged
in alignment, and transmitting said light beam through said tube.
BACKGROUND OF THE PRESENT INVENTION
The present invention relates to an analog flow meter instrument
and particularly to such an instrument for establishing an analog
electrical signal linearly related to a fluid flow.
In various operating systems, the flow of a fluid is monitored
on a continuous basis to insure appropriate functioning of the system.
The flow may be monitored by a flow meter and provide a visual readout
of the flow rate. The flow monitor or sensor may be connected into
a control system to control the flow, or provide outputs indicative
of the system condition including alarm conditions. In either system,
the flow sensor may require mounting at the machine or some other
remote location, with the signal transmitted to a remote control
station. With modern day computer designs and the like, various
digital monitors with digital transmission of the flow-related signals
have been developed and operated satisfactorily in various environments.
A typical digital system is shown in U.S. patent application "Linear
Digital Flowmeter" with Ser. No. 06/669090 now U.S. Pat.
No. 4774676 filed by Stenzel et al and assigned to a common assignee
with the present invention. Such systems are relatively complex
and thereby costly. Although digital signals are readily transmitted
over long lengths, extraneous signals may be induced into the signal
line in various commercial installations.
There is therefore a need for a less costly system which will also
provide for a reliable transmission of the flow meter signal over
relatively long lines in a manufacturing and operating environment.
SUMMARY OF THE PRESENT INVENTION
The present invention is particularly directed to an analog flow
meter instrument having means for monitoring of the flow with direct
creation of an analog signal proportional to the flow. Generally,
in accordance with the present invention, the flow meter includes
a flow responsive element coupled to a sensor unit, and particularly
to position an indicator rod-like element in an oil filled monitoring
tube. A light bar is mounted to one side of the tube and a plurality
of photosensitive current output elements are mounted in a linear
array to the opposite side of the tube. In accordance with the teaching
of the present invention, the photosensitive elements are connected
in a current summing network to generate a current signal directly
related to the position of the flow positioned rod-like element.
The output signal is amplified to produce an analog current signal,
the amplitude of which is linearly related to the fluid flow. The
analog signal can be reliably transmitted over relatively long distances
within the factory environment using conventional low voltage wiring.
The oil in the tube is generally a clear light transmitting oil
with the position related indicator providing an essentially precise
definition of the location of the flow related element. If however,
the oil becomes dirty as a result of foreign matter in the surrounding
environment, the current signal is essentially lost or at least
at a minimum becomes unreliable. The present invention monitors
the output of a selected phototransistor to detect dirty oil. The
lowermost phototransistor is advantageously selected to respond
to any settlement of foreign matter in the tube. A suitable alarm
or other output alerts the user of the condition.
In a particularly practical application, the instrument is constructed
with a housing essentially as disclosed in the previously identified
patent application, with an LED light bar and a plurality of phototransistors
to the opposite sides of the oil filled tube. The phototransistors
are secured to an analog circuit board and mounted within the housing.
Each of the phototransistors is connected through a summing resistor
to a common output line. A shaping and amplifier unit is mounted
on the board and connected to the output line to develop an output
control signal suitable for transmission to a control system.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawings furnished herewith generally illustrate the best mode
presently contemplated for the invention and are described hereinafter.
In the drawings:
FIG. 1 is a diagramatic illustration of a flow metering system
incorporating a flow meter and sensor unit with a electrical analog
output signal in accordance with the teaching of the present invention;
FIG. 2 is a view of a sensor unit forming an integrated part of
the flow meter system shown in FIG. 1; and
FIG. 3 is a schematic diagram of the readout circuit of the flow
meter unit shown in FIGS. 1-2a.
DESCRIPTION OF THE ILLUSTRATED EMBODIMENT
Referring to the drawings and particularly to FIG. 1 a flow meter
1 is illustrated connected in a flow line 2 for measuring the flow
rate of the fluid flowing through the line. The flow meter may be
constructed to monitor the flow rate of a liquid or the flow rate
of a gas. In either system, the flow meter 2 is coupled to a related
sensor unit 3 mounted to the lower end of the flow meter 1. The
sensor unit 3 generates an analog signal at an output cable 4 and
provides a direct visual output reading on a scale unit mounted
to the front of the sensor unit 3. The electrical analog signal
is transmitted over the cable 4 to various control and recording
devices 5. For example in FIG. 1 the output cable 4 includes signal
lines 6 and 7 with appropriate coupling resistors 8 to a computer
unit 9 a data logger 10 and a flow control unit 11 for controlling
of the flow.
The sensor unit 3 includes an outer housing 12 with a tube 13 aligned
with the flow meter 1. The tube 13 is filled with a suitable oil.
A float rod 14 is mounted within the tube 13 with a disk-like indicator
15 secured at the lower end and providing a visual readout of the
location of the float rod 14 within the tube 13. The float rod 14
projects upwardly from the sensor unit 3 into the flow meter 1.
The float rod 14 is moved by the flow through meter 1 with its
position within the flow meter directly and proportionally related
to the rate of flow. The indicator 15 thus is positioned within
the tube 13 in accordance with the flow rate. A suitable readout
scale 16 is provided on the front side of the housing 12 immediately
adjacent a slot 17 exposing the tube 13. The housing 12 projects
laterally from the enclosed tube. An LED light bar 18 is secured
within the one side of the housing 12 shown to the left in alignment
with the tube 13. A phototransistor bar 19 is secured to the opposite
side of the housing 12 in alignment with the two. The LED light
bar 18 includes a bank of longitudinally spaced LED's 20 to form
a continuous bar or beam 21 of light transmitted to and through
the tube 12 and into the opposite side of the housing 12. The phototransistor
bar 19 includes a plurality of immediately adjacent phototransistors
22 mounted on a suitable support plate or board 23 and located in
close spaced relation throughout the length of the tube 12. The
float rod 14 thus functions to interrupt the light beam 21 to the
phototransistors 22 in accordance with the float related location
of the float rod 14 in the tube 12. With zero flow, the float rod
14 drops downwardly with the indicator 15 at the lower or zero flow
end of the tube 12. The float rod 14 breaks the complete light beam
21 and all of the phototransistors 22 assume the quiescent or off
state. As flow is established through the meter 1 the float rod
14 rises with the indicator moving upwardly within the tube 12
and the indicator 15 provides visual readout of the flow rate on
the scale 16. Simultaneously, the upward movement of the rod 14
and indicator 15 exposes and allows the transmission of the light
beam 21 through the lower portion of the tube 12 to provide corresponding
energization and activation of the phototransistors 22.
The housing structure, the light bars and the support of the phototransistors
can all be made in accordance with the previously identified patent
application. The basic structure of the flow meter with the visual
output indicating unit is also disclosed in U.S. Pat. No. 4440028
which issued Apr. 3 1984 to Ralph W. Ramlow and is assigned to
the assignee of the present invention.
The above application discloses a digital output with a corresponding
digital logic system for transmitting of the control signal to various
devices. The present invention is particularly directed to an analog
signal output generator circuit for directly generating an analog
signal in accordance with the output of the bank of phototransistors.
The illustrated sensor unit 3 includes a sensing circuit 25 shown
in FIG. 3 having a voltage dividing network 26 connected to a low
voltage supply line 27. The network 26 includes two series connected
fixed resistors 28 and 29 and an adjustable series connected potentiometer
30. The series connected resistors 28-30 are connected between the
positive 15 volt DC supply line 27 and ground 32. A small capacitor
33 is connected between the supply line 27 and ground to protect
the circuit, eliminate transient signals and the like.
Each of the phototransistors 22 is illustrated as a NPN transistor
having a collector-to-emitter circuit 34 connected in series with
a resistor 35 in an output branch circuit 36. Each branch circuit
36 is connected in parallel with each other and in parallel with
the series resistors 28-30. Each of the phototransistors 22 has
its base 37 exposed and aligned with the light beam 21. The phototransistors
22 are normally off and non-conducting with a dark base. When the
light beam 21 is broken, the corresponding phototransistor 22 is
therefore non-conducting or off and the corresponding resistor 35
is effectively removed from the circuit. When the light beam 21
is passed through the tube 12 onto the corresponding phototransistor
22 the exposure of the base 37 to the light generates a current
of a selected level. The parallel circuit and connection of the
resistors 35 provides for summing of the individual currents to
form a low level output current linearly proportional to the location
of the rod 14 and indicator 15 and therefore of the flow rate. This
is a small but accurate current signal.
The summed current is applied to a suitable operational amplifier
38 and amplified to provide an output current which varies linarly
between a low or zero flow reading and a maximum flow reading of
the sensor unit.
In the illustrated current, the inverting input 39 of the amplifier
38 is connected to ground in series with a potentiometer 40 in series
with a fixed resistor 41 and in parallel with an output resistor
42. The potentiometer 40 provides for adjustment of the maximum
output of amplifier 38. In a typical application, the amplified
output current may vary between 4 millamp (Ma) and 20 Ma as a typical
range. With the indicator 15 at the lowest level breaking the complete
light beam 21 an output of 4 Ma is established across the output
terminals of the amplifier.
The potentiometer 30 adjusts the minimum output current level with
all of the phototransistors turned off. In the typical application,
the output level equal to 4 Ma is provided.
Thus, in the illustrated embodiment of the invention, the DC current
loop with a current range of 4 to 20 Ma DC is compatible with standard
current instrumentation widely used in industry. A single output
is illustrated with the positive and negative signal lines 6 and
7. The voltage compliance is 20 volts permitting resistive loads
up to 1000 ohms. With the positive and negative signal lines, the
output is a current loop floating above ground. The output signal
must therefore be interconnected through the coupling resistors
8 and not tied directly to power supply ground.
The system preferably includes a dirty oil indicator to generate
an output signal if the oil in tube 12 prevents transmission of
light beam 21 and thus gives a false output with the indicator rod
14 displaced from within the light beam 21. An amplifier 43 is illustrated
connected between the common line from the 15 volt power supply
and the collector of a selected phototransistor 22a. The phototransistor
22a selected is the first phototransistor at the low end of the
unit 3 or one of the phototransistors spaced from the first phototransistor.
The amplifier 43 is biased to provide an output signal with the
transistor off. The output of amplifier 43 is connected to energize
a dirty "oil" lamp 44. If the indicator 15 moves past
the selected phototransistor 22a without providing a summing signal,
the amplifier 43 continues to conduct and energizes the dirty oil
light 44. The amplifier 43 is connected to the power supply through
an appropriate potentiometer 45 to preset the signal level necessary
to operate the dirty oil lamp, and allows factory calibration of
the unit to insure accurate detection of the condition of the oil.
The dirty oil indicator lamp 44 is preferably an LED lamp mounted
within the phototransistor chamber of housing 12 and when energized
is visable at the lower end of the sight glass tube 13. The LED
lamp 44 is illuminated with the unit at zero flow and will continue
to be illuminated as the indicator moves from zero flow if the oil
level is so dirty as to interfere with forming the desired linear
output signal. Thus, the movement of the indicator from the zero
phototransistor and the selected phototransistor 22a should operate
to turn on the selected phototransistors. When the phototransistor
22a turns on, the voltage at the collector decreases and the "dirty"
oil amplifier 43 compares the voltage to the reference voltage at
potentiometer 45. With clean oil, the comparator turns off the lamp
44. As the oil becomes dirty, the level of conductivity of the phototransistor
22a is less and the voltage at the collector increases. At a selected
level of dirt in the oil, the voltage rises above the reference
voltage at the potentiometer, and 1 and 44 remains "on".
The output amplified signal is transmitted via the output lines
6 and 7 to the several output devices. The line can be a simple
low voltage wire such as 20 to 22 gage. The length and guage of
the wire is not critical nor is sheathing required other than in
environments where extreme electrical interference is anticipated.
Thus, the present invention which uses a direct analog signal transmission
is not sensitive to extraneous signals such as encountered in digital
signal transmission systems.
The adjustable factory calibrating potentiometers are mounted to
the circuit board within the housing and preferably locked in place
to permit only factory adjustment.
The output signal can be readily correlated by the user at all
times to a visual inspection of the readout on the sensor unit.
In the event of any electronic or electrical problems not only within
the unit but within the total installation, the user can conveniently
and readily observe the flow rate on the sensor unit and provide
any necessary adjustments on a manual basis. Thus, the loss of the
automatic control does not totally shut down and require a shut
down of the system but can provide for continued manual response.
The illustrated embodiment includes the oil filled tube. The sensor
may be operated without oil, and with air or ther medium. Certain
applications such as monitoring the flow of oxygen may require the
sensor to operate filled with the medium being monitored.
Various modes of carrying out the invention are contemplated as
being within the scope of the following claims particularly pointing
out and distinctly claiming the subject matter which is regarded
as the invention.