CA1198776A - Electrical joule meter and accumulator - Google Patents

Abstract

ABSTRACT
A device which takes an alternating or direct signaling current from a sensor and when integrated to a predetermined maximum establishes a quantifiable event. The input to this device can be a low level current coming from a sensor such as; a current transformer, photocell, thermistor, solar cell, radiation sensor, direct current sensor, microphone or other alternating or direct current output sensing device. The low level input current is processed through a precision rectifier, an analog integrator and a Schmitt trigger which sets the time base, to generate an output pulse when an appropriate number of Joules have been accumulated.

Description

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This invention can be related to measurement of electrical energy, ~or exa~ple, ln volt-Joules or kilowatt-hours. It accumulates such measurements and then when a maximum accumula~ion has occurred a consistent and predict-able event in the form of a pulse is generated. The input to this device can be a low current function of the power carried in a conductor conveying direct or alternating voltage and the current function can be derived from a current sensor. Such a current sensor may be a current transformer, photocell, thermistor, solar cell, radiation sensor, direct current sensor, microphone or other alternating or direct current output sensing device.
Vnited States Patent 4,039,897 issued August 2, 1977 to J.E. Dragoset, discloses a system for controlling power by sensing the power during a half cycle and to the provision of output signals proportional to the voltage and current across and to the load. The output signals are multiplied and a resultant product signal is compared to a reference signal and time integrated and fed to a pulse width modulator.
United States Patent 4,055,803 issued October 25, 1977 to Raymond L. Kraley, et al discloses a simultaneous watt or VAR indicator and includes current and voltage trans-formers and a modulator.
United States Patent ~,080,568 issued March 21, 1378 to L.L. ~unk discloses an energy monitor wherein a voltage/
proportional to the load current, is generated and conveyed to a linear voltage controlled oscillator. A waveform derived by a counter from timing pulses provided by an electronic clock circuit gates the output of the VCO to a counter, and also provides for alternation of a display hetween a representation of energy consumed and time of day.
Se~ective adjustment of the ~oltage to frequency converting circuit's gain provides an output indication in appropriate electrical or monetary units. All gatin~ and resetting of counters, display multiplexing and timekeeping functions are provided by the electronic clock circuit. This patent ~r~

98'7'i~6 disclQses only limited similarity with the present invention, that is in the generation of a voltage proportional to the load current and converts this voltage into a ~requency via a voltage controlled oscillator. The pulse counting net-work counts the number of waves generated and using a variably set gated counter counts until "an event" is completed (ie the total number of wave co~ts occurs). A pulse output would then result in a single increment when the ~ave counter resets to zero. On the other hand, the present invention converts the voltage to a linear charging current of an integrator. Then when an adequate amount of integration occurs the total allowable system voltage (which can be variably s~t via ~ presettable time base or variable integration speed is achieved. Then the integrator is reset to a pre-determined base voltage by the Schmitt trigger~ A pulse results and again the display can be incremented.
In summary, the U.S. patent in question relies on a voltage controlled oscillator and counter ~or accuracy, whereas the "citameter" relies on a precision integrator and Schmitt trigger for accuracy. That is how the two circuits di~fer. The result is that the present invention can perform the same result substantially more reliably, with lower enqr~y consumption and in a more cost effective manner.
The meter described in United States Patent 4,080,568 is most unsatisfactory since it relies on the linearity o~
the voltage controlled oscillator and such linear ~C
oscillators are extremely difficult to build. In addition, the circuitry of the disclosure of this patent is complex, expensive, re~uires high tolerance components and is not susceptible to mass production.
United States Patent 4,224,671 issued September 23, 1980 to Fumio Sugiyama discloses an electronic watt hour meter which again mulkiplies curren and ~oltage signal and puls~-width modulates the voltage signal. The current signals are integrated and the counter decodes and establishes a display signal. This apparatus is merely a 7~

relatively complicated watt~hour meter which employs arithmetic operation.
One object of the invention is to provide an accurate, simple and inexpensive electrical Joule meter which over-comes the deficiencies residing in the above-discussed prior art.
Another object of the invention is ~o provide a Joule meter which may be operated from signals derived from current and voltage transformers, radiation sensors, heat or light sensitive cells and microphones.
Another object of the invention is to provide a device for measuring and accumulating energy consumption which is reliable and portable and susceptible to the use of integrated circuits.
Another object of the invention is to provide a device to interface a signal current from a sensor with a computerized monitoring device.
A preferred embodiment of ~he invention will now be described with reference ~o the accompanying drawings in which:
Fig. 1 is a block diagram of the circuit used in the invention;
Fig. 2 is a circuit diagram of an example of a sensorO Vsing this type of sensor the circuit diagram displays the connection be ween a single phase mains voltage source and a load, showing a current transformer connected to one side of the line;
Fig. 3 is a circuit diagram of an absolute value converter stage;
Fig. 4 is a circuit diagram of an analogue integrater stage;
Fig. 5 is a circuit diagram of a Schmitt txigger stage;
Fig. 6 is a circuit diagram of an example of a pulse counter and count accumulator to di~play interface, and Fi~ 7 is a circuit diagram of the complete circuitry of t~e device;
Referring to Fig. 1, the device is divided into thre~ distinct sub-circuits compri ing a precision absolute value converter 200, a pre~ision analogue integrator 400 ''~ ,~l 3'7'~qi a Schmitt trigger 500. The input may be obtained ~rom a current transformer (which will be used as an example in this disclosure1 or other sensor. Fig. 2 shows the derivation o~ a voltage ~1 to be applied the input of the circuit shown in Fig. 1. A current transformer 20, having a single turn primary coil 22 and a secon~ary coil 24, may have a l:N turns ratio. The secondary coil 24 is terminated by a resistor R301 (shown in Fig. 3) in an absolute value converter stage, so that the output voltage is:
1 = (Ip - excitation current) R/N (The excitation current is very small with respect to any registerable values of Ip)~
Since it is intended that the device be used with selected s~andard line voltage, i.e~ 115 volts, 220, 440, etc., the sensing of line current provides, with the line voltage, a product which is proportional to the in-phase power transmitted. Integration of the product, over a selected period, provides a summation of the energy which may be in Joules, watt-seconds, kilowatt-hours, foot-pound-seconds, etc.
Referring now to Fig. 3, the simplified circuit diagram of an absolute value converter stage (200 in figure 1 is shown. The function of this stage is to take any current Is whether it be positive or negati~e r generate a proportional voltage on the positive input terminal of operational amplifier 30 and cause a proportional (but positive only) voltage across capacitor C302. Capacitor C301, is used only to suppress high frequency line trans-missions. Operational amplifier 30 is used as a standardizing buffer and is not required for lower accuracy metering.
Operational amplifier 35 and its two f~edback diodes D301 and D302 do the actual absolute value converting. The output of operational ampli~ier 30 is rectified then fed back to its input to assure unity gain and i6 fed to the absolute value converter stage output V2. The capacitor C303 is to assure a no ripple d.c. output. The potentiometer P301 trims the entire device for manufacturing tolerances~

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The precision integrator 400 in Fig. 1 will now be described. Ref~rring now to Fig. 4, the output V2 from the converter (20-0 in FigO 1~ is fed to an operational amplifier 40 via a resistor R408. The output from the integrator is present across terminals VT and V3 and the capacitor C409 sets the time base of the integrator as follows:
R408.C409 = t The integrator receives the voltage V2 and converts it to a constant charging current through the capacitor C303 in Fig. 3. The value of the voltage at V3 lowers as the capacitor C303 is charged and this changing voltage is monitored by the Schmitt trigger, 500 in Fig. 1, now to be described with reference to Fig. 5.
The output ~73 from ~he integrator, shown in Fig. 4, is applied to an operational amplifier 550 via resistor R505.
The output of the operational ampli~ier 550 is fed to the base of a transistor T501 via resistor R5090 The Schmitt trigger circuit maintains a consistent time base. This is accomplished by keeping V4 low until V3 is low enough to be equal to V+~ Then V5 goes high causing the transistor T501 to conduct. Since the capacitor C409 is connected across VT and V3 (see Fig. 4) C409 is thereby discharged as C303 discharges, V3 rises until preset voltage is achieved internally in the Schmitt trigger. The transistor T501 stops conducting as V4 goes low and the process is repeated. V4 is also utilized to activate an indicator.
Fig~ 6 shows the interface between the Schmitt trigger output and a LC~ display 600. Although the display is not part of the patent, the desired action would be: the pulses V5 are applied to an integral pulse count and accumulator 620 which may be an ICM 7224 (Manufactured by Intexsil Inc.) The ICM 7224 provides 29 segment outpu s and a backplane driver output, generating the zero d.c.
component signals necessary to drive a conventional 4 1/2 or less digit liquid crystal display 600~ This device al50 includes a complete RC oscilla~or and divider chain to 7~

generate the backplane frequency. This device may be a CM~S 4 l/2 digit counter including decoders, output latches, display dri~ers and reset circuitry. In summary the ICM 7224 will take an input pulse, count and display the total number of pulses presented to it.
Fi~. 7 is a circuit diagram of the three stages together, using four standard operational amplifiers, a description is deemed unnecessary~
Examples of applications of the subject invention:
a) A current transformer generating output resulting from a.c. feeders, current would provide input for this device which would in turn be processed through this device so that once 313 Joules were accumulated, an output pulse would be generated. Once one hundred of these pulses have occurred at an average of 115 Volts one kilowatt hour has been measured, b) A direct current sensing device resulting from a battery and/or battery charging system would provide input for this device ~hich would in turn be processed through this device so that the number of Joules used or gen-erated would be accumulated and the battery' 5 energy level can be quantified, a charging system could be turned on or off at a predetermined level which would be a function of the amount of energy removing out of that battery's potential energy capacity. Alternately, after an appropriate energy level is indicated as used by the invention, a modification of the current it is monitoring to alternate supplies or uses, is possible.
c) A radiation sensor generating output resulting from radioactive emissions would provide input for ~his device which would in turn be processed by the inven-tion so that the number of millirems is not only sensed but also accumulated over time and the level of this accumulation c~n be quantified and~or a resulting reactiQn initiated.
d) A solar or photo cell generating output resulting from light intensity ~ould provide input for the Electrical 7'~

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Joule Mete~ ~cc~eter and Indicator which would in turn fie prQcessed ~y the E.J~M.A ~nd I so that the amount of light o~er a ti~e period is accumulated for quantif-icati~n and~or resulting action such as ending a photo-grap~ic development process, turning off the lights in a green~ouse, protection of a painting from the fading process, etc.
e) A microphone generating output resulting from acoustic pressure would provide input for the E.J.M.A &I whioh woul~
in turn be processed by the invention so that the amount of acoustic pressure totalled over time (i.e. decibel seconds~ could be quantified and a possible action initiated such as, turning down the volume level, turning off the noise-source (eg. machinery) could-be ini~iated ~efore serious ear or other damage resulted.
Further, because of the invention, the cost of measuring, accumulating and triggering the xeaction is reduced, to ~t least l/lOth of alternative methods when it is used in its integrated circuit form. Certainly, ~hrough the use o~ combinations of other devices the accumulated measurement of ~nergy used, in its various forms, is possible. However, with the pres~nt inven~ion, similar accuracy can ~e accomplished at extremely low cost with increased reliaBility and portability due to the use of ~he limited number of discr~te, xeadily available, components required. The ability to function accurately with so few components is a result of the adapted Schmitt trigger functioning for low level operation and so will easily adapt itself to integrated circuit operations, or f) An interface for transferring signal current rom a ~ensor to a computerized monitoring device.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An electrical energy measuring and/or indicating device comprising:
i) absolute value converter means connected to receive a voltage, V1, which varies as a function of the energy being measured, said converter means producing a voltage V2 which is proportional to the absolute value of said voltage V1.
ii) integrator means connected to receive said voltage V2, said integrator means having a set time base t and which converts the voltage V2 into a charging current, said charging current being applied to a capacitor, said capacitor having a voltage V3 thereacross which reduces as the said capacitor is charged, and, iii) a Schmitt trigger circuit connected to receive said voltage V3, said trigger circuit providing a consistent time base and producing output pulses V4 the number of pulses varying in response to value of voltage V3.