GB1561845A - Energy monitoring systems for electrical devices - Google Patents

Description

(54) IMPROVEMENTS IN ENERGY MONITORING SYSTEMS FOR ELECTRICAL DEVICES (71) We, BRITISH NUCLEAR FUELS LIMITED, a British Company, of Risley, Warrington, Cheshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to monitoring systems for plant having a plurality of electrical devices, and more particularly for monitoring the electrical energy consumed by the electrical devices.

According to the present invention, there is provided a monitoring system for a plant having a plurality of electrical devices arranged to be energised by a common alternating current supply and to operate under substantially the same load conditions, the system comprising monitoring means for each device for monitoring the rate of consumption of energy by the device and providing an output signal proportional to said rate, the monitoring means having a first means for connection to the supply and adapted to provide a first output of coincident equal amplitude positive and negative rectangular pulses having a repetition rate greater than the supply frequency and which have been pulse width modulated by either the voltage or the current supplied by the supply, the pulses after pulse width modulation varying in width between the maximum positive and negative supply voltage or current half-cycles in proportion to the height of the respective supply voltage or current waveform from a datum position on the waveform, the monitoring means having second means for deriving an output signal proportional to the supply current or voltage to the device, the current being selected when the first output has been pulse width modulated by the supply voltage and vice-versa, a positive and a negative gating means connected between the first output and said output signal for arranging amplitude modulation of the first output by the output signal, and an integrator means to which the amplitude modulated output is arranged to be supplied for providing an integrated output signal proportional to the energy consumed by the device, and a display means to which the output signals are arranged to be supplied for enabling a comparison of the output signals to be made by an observer and thereby the detection of any difference in rate of energy consumption of a said device from that of the other devices.

The invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 shows in block diagrammatic form a monitoring system for an electric device; Figures 2a to 2e show the waveforms at different stages of the operation of the system shown in Figure 1; Figure 3 shows a circuit diagram of an arrangement for providing a light signal from the output signal provided by the system of figure 1; Figure 4 shows in block diagrnmmatic form monitoring systems of Figure 1 arranged as a system to monitor a plurality of electric motors; Figure 5 shows a pictorial representation of an arrangement for recording and displaying output signals from the monitoring system of Figure 4; Figures 6a and 6b show circuit diairnms of part of the arrangement of Figure 5; Figure 7 shows a block schematic diagram of the operation of the circuits shown in Figures 6a and 6b; Figure 8 shows a raster used in the arrangement of Figure 5, and Figure 9 shows in block diagrammatic form an alternative monitoring system to that shown in Figure 4.

In the above Figures like parts have like numerals.

Referring now to Figure 1, part of the monitoring system for an electric device, for example an electric motor 10, energised by an alternating current supply 11 of substantially constant voltage, has a first means in the form of a pulse generator 12 connected in parallel across the supply 11.

The pulse generator 12, for example an operational amplifier connected as an oscillator, provides coincident equal amplitude positive and negative rectangular pulses which are arranged to be modulated in width as a function of the supply voltage, varying from zero width at a datum represented by maximum negative supply voltage to maximum width at maximum positive supply voltage. The repetition rate of the pulses from the pulse generator 12 is arranged to be greater than the supply frequency, for example, twenty times greater than the supply frequency. The positive and negative output lines from the pulse generator 12 are connected to gating means in the form of oppositely arranged diodes 16a and 16b respectively.

A second means in the form of a current transformer 13 is arranged to be energised by the supply current to the motor 10 and to provide an output voltage proportional to the supply current. The output voltage is gated by the diodes 16a and 16b so that on one half-cycle of output current it amplitude modulates the positive pulses from the pulse generator 12 whilst the negative pulses are suppressed by diode 16b, and on the other half-cycle it amplitude modulates the negative output from the pulse generator 12 whilst the positive output is suppressed by diode 16a.

The subsequent pulse width and amplitude modulated output is fed to an integrator 14, for example a capacitance integrator, whose substantially direct current output signal 15 represents the integrated pulse area of the pulse width and amplitude modulated output with time. Since the aforedescribed pulse width and amplitude modulation of a signal is equivalent to the multiplication of voltage and current required in a wattmeter, the output signal 15 is proportional to the electrical energy consumed by the motor 10 and can be used to enable deviations in energy consumption and thereby the performance of motor 10 to be maintained. A graphical representation of the aforedescribed description is shown in Figures 2a to 2e to which reference is now made.

Figure 2a represents the graph of the supply voltage waveform and shows the datum of zero voltage. Figure 2b represents a graph of the coincident positive and negative rectangular pulses from the pulse generator 12 at a repetition rate shown for clarity ten times greater than the supply frequency, the pulses being modulated in width in proportion to the height of the voltage waveform of Figure 2a. Figure 2c represents the graph of the current waveform to the machine and thereby the output voltage from the transformer 13, the phase angle being represented by "ç". Figure 2d represents the amplitude modulating effect of the output voltage from the current transformer 13 on the gated positive and negative pulses from the pulse generator 12, and Figure 2e represents the substantially direct current output waveform from the integrator 14, the broken line indicating the mean direct current output.

To monitor the performance of the motor 10, the output signal 15 may be connected to an oscilloscope (not shown), a milliameter or a recording instrument (not shown), for example, an electro-mechanical chart recorder so that a visible permanent presentation of the output signal 15 as a function of time is obtained.

In an arrangement shown in Figure 3 to which reference is now made, the output signal 15 from the integrator 14 is connected through a resistor 17 to the base of an n-p-n junction transistor 18 controlling the brightness of a light emitting diode 19 through a resistor 20 connected to the collector of the transistor 18 so that variations in the value of output signal 15 result in a corresponding change in the brilliance of diode 19. A variable resistor 21 connecting the emitter of the transistor 18 to earth sets the initial brilliance of the diode 19, whilst a negative potential source is connected to the emitter circuit through a resistance 22.

A plurality of devices 10 supplied from a common voltage source and arranged to operate under substantially the same load conditions are monitored for energy consumption as shown in Figure 4 to which reference is made.

The electric supply 11 in the circuit shown in Figure 4 provides the current for several electric motors 10 (two only being shown in the Figure) by way of parallel circuits 25, and a current transformer 13, integrator 14 and gating diodes 16a and 16b are provided for each machine 10. The pulse generator 12 is arranged to provide coincident equal amplitude positive and negative rectangular pulses which are pulse width modulated by the supply voltage for the parallel arrangement of gating diodes 16a and 16b to which the current transformers 13 are connected to provide an amplitude modulated input to the respective integrator 14. The integrated output signal 15 from each integrator 14 is supplied to a comparing means 27, for example an electro-mechanical chart recorder, so that the records of the output signals 15 grouped together on a chart enables deviations in performance of individual motors 10 to be ascertained.

In an arrangement shown in Figure 5 to which reference is now made, the output signal 15 from each integrator 14 (not shown) of a monitoring system is converted into a light signal by a light emitting diode 19 as shown in Figure 3 to which reference may be made, and the plurality of diodes 19 grouped together and displayed as a matrix in a comparing means having a multi-channel display means 30 for direct viewing and a video camera 31 for recording the matrix in a video recording unit 32.

A camera mixer means 33 connected between the video camera 31 and recording unit 32 and synchronised by a unit 34 enables several monitoring systems (not shown) to be recorded simultaneously in a single recording unit 32. The recorded video picture in the recording unit 32 may be played back through a readout selector 35 and displayed as a matrix of light dots 37 on a monitor screen 36, for example, at the same speed as the input speed to the recording unit 32, or at a faster or slower speed, or as still pictures, to provide an opportunity for the detection and detailed examination of transient signals after their occurrence. The video signals represented by selected light dots 37 on the screen 36 may be converted into equivalent electrical signals by the readout selector 35 for connection to an amplifier 38 and a multichannel chart recorder 40 or an oscilloscope (not shown).

Selection of the required light dots 37 is made by the use of movable square marker elements 41 (four being shown in Figure 5) which may be positioned over selected light dots 37 by simple adjustment at the readout selector 35 of a horizontal shift control 42 and vertical shift control 43 associated with each marker element 41. Once the marker elements 41 are positioned over their respective light dots 37, only the video signals to these selected light dots 37 are converted to equivalent electrical signals.

Circuit diagrams of the readout selector 35 are shown in Figures 6a and 6b, and referring now to Figure 6a, the video signal from the video recording unit 32 (not shown) is fed to a capacitor C1 and to the base of a transistor T1 having its collector joined to a 5V supply and its emitter connected to the base of a transistor T2. Resistors Rl, R2 are connected in parallel one either side of the capacitor C1 to earth potential and resistor R3 connected to earth potential from the emitter of transistor T1. Resistor R4 is connected to the 5V supply from the collector of T1.

The emitter of transistor T2 is connected to the 5V supply whilst the collector of T2 is joined through a capacitor C2 to the input of a Schmitt limiter S1 the output of which is connected to the base of a transistor T3 through a resistor R5, transistor T3 having its emitter at earth potential and its collector joined both to the input of a Schmitt limiter S2 and through a resistor R6 to the 5V supply whilst a capacitor C3 is connected in parallel across the resistor R6.

A transistor T4 has its base connected to a tapping between the emitter of transistor T1 and the capacitor C2 through a capacitor C4, the collector of the transistor T4 being connected to the 5V supply and the emitter through a capacitor C5 and resistor R7 to the composite video output terminal CV2. Resistor R8 and R9 are connected in parallel at the base of transistor T4 to the 5V supply and earth potential respectively.

A diode Dl is connected between resistors R10 and Rl 1 which are connected between capacitor C2 and the base of transistor T2 and earth potential.

A resistor R12 is connected between the emitter of transistor T2 and earth potential, and a resistor R13 connected between the emitter of transistor T4 and earth potential.

The outputs from Schmitt limiters S1 and S2 are connected to terminals L and F respectively which may be connected to identical circuits in parallel, one of which is shown in Figure 6b and to which reference is now made. In Figure 6b, terminal L is connected to a timer TC1, and terminal F connected to a timer TC2. Timer TC1 is connected through a resistor R20 and variable resistor VR 21 to a 5V supply and through capacitors C20 and C21 to earth potential. The output from timer TCl is connected through a capacitor C22, diode D20 and capacitor C23 to the base of a transistor T20, having its emitter at earth potential. Resistors R22 and R23 are connected between either side of diode D20 and earth potential. The collector of transistor T20 is connected to the input of a Schmftt limiter S20 having its output connected to a gate G20 whose output is fed to another gate G21. The collector of transistor T20 is also connected through a resistor R24 to the 5V supply and has a parallel connected resistor R25.

Timer TC2 is connected through a resistor R26 and variable resistor VR27 to the 5V supply and through capacitors C24 and C25 to earth potential. Timer TC2 provides an output through a capacitor C26, diode D21, and capacitor C27 to the base of a transistor T21 having its emitter at earth potential. Resistors R28 and R29 are connected between either side of diode D21 and earth potential. The collector of transistor T21 is connected to the input of a Schmitt limiter S21 having its output connected to a gate G22 whose output is fed to the gate G21. The collector of transistor T21 is also connected through a resistor R30 to the 5V supply and has a parallel connected resistor R3 1. The output of gate G21 is fed to a gate G23 connected to a terminal P1.

Referring again to Figure 6a, terminal P1 of Figure 6b is connected to a tapping in the connection between the resistor R7 and the composite video output terminal CV2, and an analogue switch SWl, the connection having a resistor R14 arranged in series. The analogue switch SW1 is connected to a tapping between the capacitor C4 and the emitter of transistor T1.

The analogue switch SW1 also provides an output to the base of a transistor T5 through a capacitor C7, the transistor T5 having its emitter connected to earth potential and its collector connected to a signal out terminal SO1. Resistors R15 and R16 are connected between either side of the capacitor C7 and to earth potential. The collector of transistor T5 is also connected through a resistor R17 to the 5V supply, and a resistor R18 and capacitor C8 are connected in parallel between the base of the transistor T5 and the 5V supply, a connection being made between the resistor R18 and capacitor C8 and the signal out terminal SO1.

The operation of the readout selector 35 may be more easily understood from the block schematic diagram of Figure 7 to which reference is now made. The video signal from the video recording unit 32 (not shown) is fed to an input emitter follower circuit 70 which provides an output signal to an output emitter follower circuit 71 which in turn provides a signal to the monitor 36 and to an analogue switch 77.

The input emitter follower circuit 70 also provides a signal to a line sync separator 72 and a frame sync separator 73, the line sync separator 72 then being connected in parallel to four horizontal shift control circuits 74 (only one being shown for clarity) and the frame sync separator 73 being connected in parallel to four vertical shift control circuits 75 (only one being shown for clarity) to control the position of the four marker elements 41 (see Figure 5).

The outputs of the horizontal shift control 74 and the vertical shift control 75 are connected to a marker generator circuit 76 whose output is connected to the analogue switch 77, to gate the switch 77, and at the same time is added to the video output to the monitor 36 to generate the marker element 41. The gated analogue switch 77 provides an output to an integrator 78 which integrates an entire video signal within a respective marker element 41 to provide an output to the amplifier 38 which is connected to the multi-channel chart recorder 40.

A simplified raster for one marker element 41 is shown in Figure 8 to which reference is now made, and illustrates the fixed horizontal and vertical pulse widths and the variation produced by operation of the variable horizontal and vertical variable shifts respectively of Figure 7.

Referring again to Figure 7 and Figure 5, the horizontal and vertical shift control generate pulses of fixed widths and are coordinated in gate circuits (not shown) which allow only the pulses forming the required position of the marked element 41 to be present at the output from. the marker generator circuit 76. This output then control the analogue switch 77 and also brightens up the area on the monitor 36 so as to show which light dot 37 is being selected. The video sample is taken over three consecutives lines of the raster shown in Figure 8 and, therefore, consists of three consecutive pulses, whose height is proportional to the signal level. The three pulses are integrated in the integrator 78 to form an average value for the area and the final integrated signal, which is a video pulse, is then recorded.

It will be understood that the readout selector 35 enables a video signal to be sampled directly land independently of the monitor 36 brightness and contrast (not shown).

Although the invention has been described in relation to the use of four marker elements 41, an alternative number of marker elements 41 may be used.

As an alternative to the use of the readout selector 35, the intensity of the light dots 37 on the monitor 36 may be detected by a photo-probe (not shown) to derive an electrical signal, for example, for a multichannel chart recorder 40, or oscilloscope (not shown).

Although the invention has been described by way of example with reference to its use for monitoring electric motors, it also has applications for monitoring the electrical energy consumption of other alternating current electrical devices.

The invention has been described in relation to the use of an operational amplifier as the pulse generator means but other pulse generator means may be used, for example a transistor arranged to operate as a pulse generator.

Although minimum negative voltage has been used in the aforedescribed example as the datum from which the height of the supply voltage waveform has been measured upwardly to determine the proportions of the widths of the modulated pulses, other datums may be used, for example, maximum positive supply voltage or open circuit voltage at the cross-over position on the time base of the waveform.

In the case of maximum supply voltage when used as a datum, the height of the waveform is measured downwardly from the datum so that maximum pulse width occurs at maximum negative supply voltage.

On the other hand when the cross-over position on the time base is used as a datum, the height of the waveform is measured from the time base as positive or negative heights, and the pulse widths are increased with positive height from a datum width at zero height and decreased in width with negative height or vice versa to suit the application.

It will be appreciated that the invention may also be used in a reverse arrangement to monitor the electrical energy consumed by a plurality of devices in applications where the value of the current is the factor common to all the devices, and variations in voltage across individual devices represent differences in performance of the individual devices.

An example of such a reverse arrangement is shown in Figure 9, and referring to Figure 9, the circuit shown is similar in many respects to that shown in Figure 4 but the electric motors 10 (two only being shown) are now arranged in series and a signal, dependent upon the load current, is fed from a current transformer to the pulse generator 12. The pulse generator 12 is arranged to provide coincident equal amplitude positive and negative pulses which are pulse width modulated by the supply current, for the parallel arrangement of gating diodes 16a and 16b. Each electric motor 10 is provided with a voltage trans former 50 whose output is connected to a respective pair of gating diodes 16a and 16b to provide an amplitude modulated input to the respective integrator 14. The integrated output signal 15 from each integrator 14 is supplied to a comparing means 27 as in the case of the circuit shown in Figure 4, to enable deviations in performance of individual motors 10 leading to deviations in the output from a respective voltage transformer 50 to be ascertained.

WHAT WE CLAIM IS: 1. A monitoring system for a plant hav ing a plurality of electrical devices arranged to be energised by a common alternating current supply and to operate under substantially the same load conditions, the system comprising monitoring means for each device for monitoring the rate of con sumption of energy by the device and pro viding an output signal proportional to said rate, the monitoring means having a first means for connection to the supply and adapted to provide a first output of coincident equal amplitude positive and negative rectangular pulses having a repetition rate greater than the supply frequency and which have been pulse width modulated by either the voltage or the current supplied by the supply, the pulses after pulse width modulation varying in width between the maximum positive and negative supply voltage or current half-cycles in proportion to the height of the respective supply voltage or current waveform from a datum position on the waveform, the monitoring means having second means for deriving an output signal proportional to the supply current or voltage to the device, the current being selected when the first output has been pulse width modulated by the supply voltage and vice-versa, a positive and a negative gating means connected between the first output and said output signal for arranging amplitude modulation of the first output by the output signal, and an integrator means to which the amplitude modulated output is arranged to be supplied for providing an integrated output signal proportional to the energy consumed by the device, and a display means to which the output signals are arranged to be supplied for enabling a comparison of the output signals to be made by an observer and thereby the detection of any difference in rate of energy consumption of a said device from that of the other devices.

2. A system as claimed in claim 1 wherein the display means is arranged to record the output signals for subsequent representation thereof.

3. A system as claimed in claim 2 wherein the display means is arranged to represent the output signals at a different speed from that of the input speed thereof to display means.

4. A system as claimed in any one of claims 1 to 3 wherein the output signals are arranged to be provided by light signals each having a brilliance proportional to the valve of the respective output signal.

5. A system as claimed in claim 2 or claim 3 wherein sampling means are provided for selectively sampling the repre sented signals to provide an electrical output proportional to the selected represented signal.

6. A monitoring system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   the widths of the modulated pulses, other datums may be used, for example, maximum positive supply voltage or open circuit voltage at the cross-over position on the time base of the waveform.

   In the case of maximum supply voltage when used as a datum, the height of the waveform is measured downwardly from the datum so that maximum pulse width occurs at maximum negative supply voltage.

   On the other hand when the cross-over position on the time base is used as a datum, the height of the waveform is measured from the time base as positive or negative heights, and the pulse widths are increased with positive height from a datum width at zero height and decreased in width with negative height or vice versa to suit the application.

   It will be appreciated that the invention may also be used in a reverse arrangement to monitor the electrical energy consumed by a plurality of devices in applications where the value of the current is the factor common to all the devices, and variations in voltage across individual devices represent differences in performance of the individual devices.

   An example of such a reverse arrangement is shown in Figure 9, and referring to Figure 9, the circuit shown is similar in many respects to that shown in Figure 4 but the electric motors 10 (two only being shown) are now arranged in series and a signal, dependent upon the load current, is fed from a current transformer to the pulse generator 12. The pulse generator 12 is arranged to provide coincident equal amplitude positive and negative pulses which are pulse width modulated by the supply current, for the parallel arrangement of gating diodes 16a and 16b. Each electric motor 10 is provided with a voltage trans former 50 whose output is connected to a respective pair of gating diodes 16a and 16b to provide an amplitude modulated input to the respective integrator 14. The integrated output signal 15 from each integrator 14 is supplied to a comparing means

   27 as in the case of the circuit shown in Figure 4, to enable deviations in performance of individual motors 10 leading to deviations in the output from a respective voltage transformer 50 to be ascertained.

   WHAT WE CLAIM IS: 1. A monitoring system for a plant hav ing a plurality of electrical devices arranged to be energised by a common alternating current supply and to operate under substantially the same load conditions, the system comprising monitoring means for each device for monitoring the rate of con sumption of energy by the device and pro viding an output signal proportional to said rate, the monitoring means having a first means for connection to the supply and adapted to provide a first output of coincident equal amplitude positive and negative rectangular pulses having a repetition rate greater than the supply frequency and which have been pulse width modulated by either the voltage or the current supplied by the supply, the pulses after pulse width modulation varying in width between the maximum positive and negative supply voltage or current half-cycles in proportion to the height of the respective supply voltage or current waveform from a datum position on the waveform, the monitoring means having second means for deriving an output signal proportional to the supply current or voltage to the device, the current being selected when the first output has been pulse width modulated by the supply voltage and vice-versa, a positive and a negative gating means connected between the first output and said output signal for arranging amplitude modulation of the first output by the output signal, and an integrator means to which the amplitude modulated output is arranged to be supplied for providing an integrated output signal proportional to the energy consumed by the device, and a display means to which the output signals are arranged to be supplied for enabling a comparison of the output signals to be made by an observer and thereby the detection of any difference in rate of energy consumption of a said device from that of the other devices.
2. 2. A system as claimed in claim 1 wherein the display means is arranged to record the output signals for subsequent representation thereof.
3. 3. A system as claimed in claim 2 wherein the display means is arranged to represent the output signals at a different speed from that of the input speed thereof to display means.
4. 4. A system as claimed in any one of claims 1 to 3 wherein the output signals are arranged to be provided by light signals each having a brilliance proportional to the valve of the respective output signal.
5. 5. A system as claimed in claim 2 or claim 3 wherein sampling means are provided for selectively sampling the repre sented signals to provide an electrical output proportional to the selected represented signal.
6. 6. A monitoring system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.