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.

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.

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.