U.S. patent number 3,593,966 [Application Number 04/860,637] was granted by the patent office on 1971-07-20 for added-fluid-metering system.
This patent grant is currently assigned to Columbia Machine, Inc.. Invention is credited to Lonnie E. Munroe.
United States Patent |
3,593,966 |
Munroe |
July 20, 1971 |
ADDED-FLUID-METERING SYSTEM
Abstract
A system for monitoring and controlling the addition of water to
dry concrete mix. The water is added through a solenoid-controlled
supply valve to a truck-mounted mixing container rotatable by a
three-phase AC motor. The power consumption of the motor, which
decreases as water is added to the mix, is monitored by a load
sensor transducer which produces a related DC control signal. A
voltage comparator and latching circuit are provided to deenergize
the solenoid and stop water flow when the DC control signal voltage
equals a precalibrated DC reference voltage.
Inventors: |
Munroe; Lonnie E. (Mississauga,
Ontario, CA) |
Assignee: |
Columbia Machine, Inc.
(Vancouver, WA)
|
Family
ID: |
25333655 |
Appl.
No.: |
04/860,637 |
Filed: |
September 24, 1969 |
Current U.S.
Class: |
366/40 |
Current CPC
Class: |
B28C
7/026 (20130101) |
Current International
Class: |
B28C
7/02 (20060101); B28C 7/00 (20060101); B28c
007/14 () |
Field of
Search: |
;259/154,168,164,149,11,12,21,22,23,24 ;137/386 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Jenkins; Robert W.
Claims
I claim and desire to secure by Letters Patent:
1. An added-fluid-metering system comprising
an electric control value for selectively controlling the flow of
fluid from a fluid source to a load,
electric motor means for conditioning the load,
transducer means for monitoring the power consumption of said motor
due to the load and producing an indicating signal in response
thereto,
means for producing a second signal corresponding to a desired
fluid value,
comparator means responsive to said indicating signal and said
second signal for producing a trigger signal when the magnitude of
said indicating signal exceeds the magnitude of said record signal,
and
latching circuit means responsive to said trigger signal for
selectively operating said control valve.
2. A fluid-metering system as described in claim 1 further
including
a mix-ready-indicating lamp, a source and timing circuit means
responsive to said trigger signal for supplying said source to said
lamp.
3. An added-fluid-metering system as described in claim 1
wherein
said motor is adapted to be energized from a three-phase supply and
said transducer means includes probe means for sensing the current
supplied to a first phase of said motor and producing a third
signal proportional thereto, transformer means for sensing the
voltage supplied to the first phase of said motor and producing a
fourth signal proportional thereto, and storage means for combining
the in-phase portions of said third and fourth signals to produce
said DC indicating signal.
4. A metering system as described in claim 3 further including a
wet-enough-indicating lamp and circuit means for energizing said
lamp in response to said trigger signal.
5. Apparatus for monitoring and controlling the flow of liquid into
an electrically motor-driven mixer wherein the introduction of
liquid into the mixer affects the power required to drive the motor
for the mixer, and the amount of such power required is related to
the amount of liquid in the mixer, said apparatus comprising
conduit means adapted to connect said mixer to a liquid supply
including an electrically operable valve means placeable
selectively in open and closed states,
transducer means adapted to be operatively connected to said motor
operable to produce an indicating signal which reflects the level
of power supplied to the motor,
circuit means operatively interconnecting said transducer and said
valve means, operative with said transducer producing an indicating
signal reflecting power supplied the motor above a certain level to
place said valve means in one of its said states, and
with said transducer producing an indicating signal reflecting
power supplied the motor below said certain level to place said
valve means in its other state.
6. Apparatus as described in claim 5 wherein the introduction of
liquid into the mixer decreases the power required to drive the
motor and wherein said valve means is open in its said one state
and closed in its other state.
7. Apparatus as described in claim 6 further including adjustable
means for establishing said certain power level.
8. Apparatus as described in claim 7 wherein the indicating signal
produced by said transducer means comprises a DC voltage,
said adjustable means produces a DC reference voltage, and said
circuit means further includes a comparator responsive to said DC
voltage and said DC reference voltage for controlling the states of
said valve means.
9. Apparatus as described in claim 8 wherein said comparator places
said valve means in an open state when the magnitude of said DC
voltage exceeds the magnitude of said DC reference voltage and
places said valve means in a closed state when the magnitude of
said DC voltage is less than the magnitude of said DC reference
voltage.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a metering system for controlling
the amount of fluid delivered to a motor-driven mixer container for
blending with dry material, such as a dry concrete mix, in the
container. More specifically, the invention pertains to a control
system which monitors the power consumption of the motor driving
the container, and shuts off the flow of water when the level of
power consumption reflects that a proper amount of water has been
added.
In mixers for particulate materials, such as concrete mix or
foundry sand, it is desirable to provide a simple
operator-controlled system for monitoring the flow of materials,
particularly water, being added to dry material in the mixer's
container. In the case of concrete, where varied dry mixes are used
for different applications, widely varied amounts of water are
required per pound of dry mix to produce concrete having the proper
slump and other characteristics. It is, of course, possible to
calculate or to determine empirically the correct amount of water
to be added to a particularly dry mix, and then directly meter the
desired amount of water. However, this is a time-consuming and
expensive task, and accordingly is not too satisfactory.
A number of systems have been devised in the prior art to overcome
the above problem and to control fluid feed to a mixer. For
example, and in the case of preparing concrete, systems have been
designed for continuously measuring the electrical conductivity of
a concrete mixture, which increases as the mixture becomes more
moist, as an indication of wetness of the mix. Other systems have
been provided for the same purpose wherein the density of a mix is
sensed as an indication of water content. These and other systems
have not satisfactorily solved the problem, since they usually
require the use of expensive and sensitive monitoring elements
affixed within the mixing container. Furthermore, they do not
enable the fast and accurate delivery of water to the mixer by a
system which can be easily controlled or adjusted by the truck
operator.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide means for
accurately controlling the amount of fluid delivered to a
motor-driven mixer container for blending with dry material in the
container.
It is a further object of the invention to provide automatic means
responsive to the condition of a load for delivering the proper
amount of water to a mixing container containing the load.
It is yet a further object of the invention to provide in a system
of the type mentioned a transducer for monitoring the power
consumption of the drive motor for the container, and for producing
a control signal indicative of the moisture conditions of wet
concrete and to provide latch circuit means for controlling the
flow of water to the mixer in response to such control signal.
The foregoing and other objects of the invention are accomplished
by a novel system especially designed for use with truck-mounted
rotary-type mixers, though equally usable with station-type
installations. In conceiving the system described herein, the
inventor determined that the power required to drive a rotary-type
mixing container varies inversely with the amount of water added to
dry concrete mix within the container. Thus, with totally dry mix
in the container a relatively large amount of power is consumed.
However, as water is added to achieve usable wet mix the power
consumption is noticeably reduced. It is a significant aspect of
the invention that measurement of the parameter of power
consumption of an electric motor, such as are commonly used on
rotary-type mixers, is more simple and inexpensive than the direct
measurement of instantaneous moisture content in the mixing
container which has been carried out in the prior art.
In the system described water is selectively added through a
conduit from a supply to a rotary-type mixing container under the
control of a solenoid-actuated supply valve. The mixing container
may be stationed or truck mounted and is rotatably driven by
suitable means such as a three-phase electric motor. A transducer
is provided to monitor the power consumption of the motor and to
produce a DC control voltage signal directly proportional thereto.
A second signal is provided from a metered DC reference voltage
source adapted to be adjusted by the operator to a desired
calibrated value which corresponds to the proper amount of water to
be added. A voltage comparator receives both signals as inputs and
produces a trigger signal output having either a positive or a
negative polarity as determined by the relative levels of the input
signals. A power amplifier and latching circuit, responsive to the
trigger signals, is provided to selectively energize the solenoid
of the water supply valve and control water delivery.
BRIEF DESCRIPTION OF THE DRAWINGS
Other features and objects of the invention will be apparent from
the following description taken in conjunction with the
accompanying drawings, wherein:
FIG. 1 is a block diagram of the system of the invention;
FIG. 2 is a schematic diagram of a load sensor power transducer
circuit utilized in the system;
FIG. 3A is an illustrative circuit diagram used to explain the
voltage states in a portion of the load transducer under a first
set of conditions;
FIG. 3B is an illustrative circuit diagram used to explain the
voltage states in the same portion of the load transducer under a
second set of conditions; and
FIG. 4 is a schematic diagram of a power amplifier and latching
circuit used in the system.
DETAILED DESCRIPTION OF THE INVENTION
Referring now FIG. 1, a mixing container 1 is diagrammatically
shown to include a mix barrel 3 having an open top end 4 and a
discharge orifice 5. A three-phase motor 7 is provided to rotate
the barrel by means of shaft 9 when the motor is energized from
three-phase input lines T1, T2, T3, respectively. A water source 10
is provided to furnish water to the mixing container through
conduit 12 and supply valve 14. It should be noted that the mixing
container may be of any suitable type, for example either stationed
or truck mounted. Likewise it should be understood that the gate of
supply valve 14 is electrically controlled, being responsive to the
energization of a solenoid contained within the valve which
receives power from a latching circuit 15, via lines 16, 17.
A transducer 18 is provided to monitor the power consumption of
motor 7; deriving an input via terminal 26 from supply line T3, as
well as an input via terminal 27 from supply lines T1, T2 through
balancing resistors 24, 25. In addition, transducer 18 receives
inputs via terminals 30, 31 from resistor R32 bridging a probe 33
which comprises a conventional current transformer. It should be
apparent that terminals 26, 27 receive a voltage which is
substantially the same as and in phase with that existing across
the phase of motor 7 connected to line T3. Input terminals 30, 31
receive a voltage signal proportional to the in-phase component of
current in line T3. Consequently, the transducer is provided at its
inputs with the parameters which reflect power consumption in motor
7.
The output of transducer 18, which is a DC voltage substantially
proportional to motor power, serves as one input to a conventional
voltage comparator 35; while a second input to the comparator is
derived from a metered adjustable DC reference source 37. In the
embodiment illustrated, the comparator output is a fixed negative
voltage when the magnitude of the signal received from transducer
18 exceeds that of the signal from source 37, and changes to a
fixed positive voltage when the motor power declines to produce a
signal from transducer 18 having a magnitude less than that of the
reference signal. Thus, the comparator output is used to trigger
the latching circuit in response to the presence of sufficient
water in the mix. The latching circuit includes a control panel 40
having a control switch and three indicator lights. As shown the
control switch may be moved from an off position to either an
automatic or a manual position to achieve control of the mixer in a
manner to be explained. The indicator lights are energized to
indicate, respectively, wet enough, water on, and mix ready. The
significance of these indicators will also become more apparent
from a description of the operation of a cycle.
Referring now to FIG. 2 a schematic diagram of transducer 18 is
shown within the dotted outline. As previously explained the
transducer receives inputs via terminals 26, 27 from lines T3 and
T1, T2, and also via terminals 30, 31. As shown the inputs 26, 27
are connected across the primary 44 of a transformer 45, with the
secondary 47 of the transformer being connected in parallel with
resistors R48, R49. A first circuit loop is defined from the upper
terminal of secondary 47 including diode 54, the parallel
combination of resistor R55 and capacitor C56, on through bridging
resistor R32, and resistor R48. A similar circuit loop is defined
from the lower terminal of secondary 47 including diode 58, the
parallel combination of resistor R59 and capacitor C60, and
returning through resistors R32 and R49. As shown diode 54 is poled
to permit conduction on alternate negative half cycles of current
through secondary 47 (i.e., with the bottom end of secondary 47
positive relative to the top end in FIG. 2), while diode 58 is
poled to permit conduction on position half cycles. An output
terminal 65 derives a signal from the junction of diode 58 and
resistor R59 through a load resistor R64 and a filter capacitor
C63.
The transducer described is in effect a low cost, high-output watt
transducer. Thus, the voltage appearing on the secondary of
transformer 45 is derived from a resistive load and is compared to
the probe voltage which is slightly out of phase depending upon the
power factor of the motor. However, if the motor were replaced by
an equivalent resistive load the voltage from the probe would be
entirely inphase with the transformer voltage and would produce a
maximum difference in charge between capacitor C56 and capacitor
C60 in a manner to be explained. It is this voltage difference that
is monitored at the output terminal 65 as an indication of the
motor power consumption.
Referring now to FIGS. 3A and 3B, the manner in which the
transformer voltage is compared to the probe voltage is more easily
understood. Fig 3A shows instantaneous voltage conditions which
exist in the transducer circuit during the first positive half
cycle of operation. With, for example, 20 volts appearing across
each of R48, R49, a positive 5 volts appearing across R32 from the
probe, no current flows in the upper loop and current flows in the
lower loop. It should be apparent that C56 is uncharged and that
C60 is charged to a value of 15 volts of the polarity shown, since
the probe voltage bucks the transformer voltage in the lower
loop.
The instantaneous conditions existing during the first negative
half cycle are shown in FIG. 3B. With 20 volts of opposite polarity
appearing across each of R48, R49, a negative 5 volts appearing
across R32 from the probe, no current flows in the lower loop and
current flows in the upper loop. As shown the transformer voltage
and probe voltage are aiding in the upper loop and therefore, C56
charges to a value of 25 volts of the polarity shown. However, C60
has no current flow in its loop, is unaffected and instantaneously
retains its 15 volt charge. Consequently under normal operations
the probe voltage aids the voltage charging C56 and bucks the
voltage charging C60. This effect is increased by an increase in
motor current and decreased by the effects of phase shift due to
power factor, which is negligible for purposes of effective circuit
operation.
The net effect is to produce a DC voltage at terminal 65 relative
to ground which accurately reflects the power consumption of the
motor 7. Thus, under the conditions described, the transducer
produces the DC output from 0 to 10 volts depending upon the power
actually consumed by the motor, caused by motor load exclusive of
reactive current flow. This signal is compared by comparator 35
with an adjustable DC reference signal derived from source 31, as
shown in FIG. 1.
The comparator 35 is an operational amplifier of conventional
design which produces a positive voltage output when the magnitude
of the DC voltage from transducer 18 is less than that supplied by
adjustable DC reference source 37, and which produces a negative
voltage output when the reverse is true.
Referring now to FIG. 4 a schematic diagram of a power amplifier
and latching circuit utilized in the system described is shown
within the dotted outline. The output of comparator 35 is supplied
to the base of NPN transistor 70 via a biasing resistor 71. The
emitter of transistor 70 is connected to ground while the collector
is connected through a lamp 73 to a source of positive DC voltage.
The collector of transistor 70 is also connected to the base of NPN
transistor 75 via a biasing resistor 76. The emitter of transistor
75 is connected to ground while the collector is connected to
terminal 80 of switch 82 as well as to the cathode of a diode 84.
Diode 84 is connected in parallel with variable resistor 85 and has
its anode connected to the emitter of a unijunction transistor 86.
A firing capacitor 87 is connected between the emitter of the
unijunction transistor and ground while the lower base of the
unijunction element is connected to the gate of a
silicon-controlled rectifier 88. The cathode of SCR 88 is connected
to ground while the anode is connected through a lamp 90 to
terminal 81, a switch 82. The lower base of unijunction transistor
86 is also connected to ground via a resistor 92 while the upper
base is connected to the positive voltage source via resistor 93. A
diode 94, winding 95 of solenoid that controls valve 14 and lamp 96
are connected in parallel between the positive voltage source and
the upper terminal of lamp 90. As shown terminal 78 of switch 82 is
grounded and terminal 79 is open.
Under conditions of operation with the mixer empty, switch 82 of
the circuit of FIG. 4 is set in the off position and comparator 35,
with motor power at a low level, provides a positive output signal
which holds transistor 70 in a normally conducting state.
Transistor 75 is in a nonconductive state and coil 95 and lamps 90,
96 are not energized. When the mixer is filled with dry mix and
rotated the motor load increases and the resulting negative signal
from comparator 35 biases transistor 70 to a nonconductive state,
thereby providing a more positive level at the base of transistor
75. When switch 82 is closed thereafter to the automatic position
transistor 75 is biased to a conductive state, solenoid coil 95 is
energized to overcome the spring-loaded valve 14 and supply water
to the mixer, while parallel connected lamp 96 is energized to
indicate that the water is on, and lamp is extinguished.
Water is continually added until the wet concrete reaches proper
slump conditions as indicated by equality between the decreasing
transducer signal and the reference control signal. It should be
noted that the reference control signal has been preset by the
operator to a desired value determined by empirical methods or by
running an experimental batch, for example. When the reference
signal exceeds the transducer signal, the resultant switching of
the comparator output signal from a negative to a positive level
biases transistor 70 to conduction again and lights lamp 73 to
indicate the mix is sufficiently wet. Upon conduction of transistor
70 the base of transistor 75 becomes more negative and transistor
75 cuts off. With transistor 75 nonconductive, coil 95 is
deenergized stopping water flow through valve 14 and extinguishing
lamp 96. At the same time, capacitor 87 is no longer short
circuited by transistor 75 and begins charging through adjustable
timing resistor 85. After a predetermined period corresponding to a
desired mixing interval the charge on capacitor 87 reaches a value
sufficient to trigger unijunction transistor 86 and fire
silicon-controlled rectifier 88. Firing of the SCR completes the
circuit to light lamp 90 as an indication that the mix is ready for
placement.
The manner in which the metering system is used in cycles of
operation should now be apparent. It should be noted that movement
of the switch 80 to the off position permits meter reading (for
precalibration and other purposes) without water being added, and
that water flows continually while the switch is in the manual
position. While the invention has been described in connection with
a three-phase mixer motor, it is equally functional with systems
using single-phase motors.
* * * * *