Abstract:
In a remote meter reading device involving a plurality of dials, mechanical inaccuracies in the hand position are compensated for by dividing each dial into sectors, sequentially reading each dial starting with the least significant dial and adding, to each subsequent reading after the first, a correction factor based on the sector of the dial pointer of the previous reading.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to remote meter reading in general and more particularly to an improved remote meter reader which provides an accurate reading output at the meter. In U.S. Pat. No. 4,007,454, granted to Charles Cain there is disclosed a remote meter reading system which utilizes a rotating electric field concentric with the center of rotation of the meter needle. The interaction of the meter needle with this field is utilized to obtain an indication of needle position by comparing the phase of the detected signal with that of a reference signal. 
     In a meter reading device of this nature a problem may arise because of mechanical inaccuracies in the meter. As will be well recognized, most meters which must be read constitute a plurality of dials (or hands) which represent, for example, kilowatt hours, tens of kilowatt hours, hundreds of kilowatt hours and thousands of kilowatt hours. In some cases the hands are not accurately aligned. For example, if the reading of the kilowatt hand is at two, having just passed zero, the tens of kilowatt dial should be 2/10&#39;s of the digital distance beyond a significant digit, say 0.2. Due to misalignment, however, the tens of kilowatt dial may, for example, be at 9.9. If the dial readings are obtained independently, errors can clearly be carried through the system. Another approach is: data from each dial is obtained with more resolution and decoded at a central location--more data must be transmitted. 
     SUMMARY OF THE INVENTION 
     The present invention provides such a method and apparatus which insures that the reading obtained at the meter is accurate and no data beyond the reading itself for each dial be outputed and no further processing of that reading need be done. 
     Although described in terms of meters and meter needles herein, the present invention provides an error correcting system of wide application. In general, it can be applied to any type of device having equivalent operation to that of a meter. What is meant by equivalent operation is that a device must have at least two mechanically movable indicators, the position of which is remotely read or sensed. One of the indicators must represent a less significant digit and the other indicator a more significant digit in any number system. A further characteristic of the system is that the indicators are essentially continuously moveable and that movement of the less significant indicator between the two limits results in a movement of the more significant indicator over a smaller distance. Movement of the less significant indicator through the predetermined limits a number of times equal to the base of the number system in use will result in movement of the more significant indicator a distance equal to the distance between said limits. 
     If one designates the distance between the limits as X and designates the base of the number system being used as N, movement of the less significant indicator through a distance of X will result in movement of the more significant indicator a distance equal to X/N. 
     Thus, where the indicator is a dial, and the base of the number system is 10, movement of the less significant needle through 360° ten times results in the movement of the next most significant needle through 360°. 
     A further characteristic of the system is that each reading is to be rounded off. For example, when working in the base ten number system, rounding off is to the nearest whole number. Thus, if a reading of 2.5 is obtained, it is rounded off to 2. One might use as a base 36, representing the 360° of a circle. In that case, it would be desired again to have the nearest whole number. For example, if the reading was 245, representing 245 degrees, it would be rounded off to 24. 
     The error correction system of the present invention is explained in detail herein with reference to meter dials or pointers. However, this is given only as an example of what is found to be a practical embodiment of the system. It must be remembered when reading the specification that other types of mechanical indicators which are subject to mechanical error can equally well be corrected. 
     In its broadest sense, using a meter with a plurality of dials as an example, the present invention uses the position of a less significant dial between zero and 360° to generate a correction bias for the device reading for the next most significant dial reading such that it will obtain a reading which is exactly half way between the two numbers which the dial is traversing if the dial is at its exact, correct mechanical position. The reading will then be displayed as the lower of the two numbers. More specifically, this is accomplished by dividing the dial into a plurality of sectors, preferably an odd number of sectors, and by then reading sequentially each dial starting with the least significant dial and adding a correction bias to each dial reading device after the first based on the sector in which the pointer of the previous dial was located. 
     In a meter, a full rotation of a less significant dial represents movement between two numbers on the next most significant dial. For example, assume that the least significant dial represents tenths of kilowatt hours and the next most significant represents kilowatt hours. Assume that the least significant dial is at zero and the next dial is at four. One rotation of the least significant dial from zero back to zero should move the next dial from four to five. Furthermore, when the least significant dial is at the number eight, the next most significant dial should be eight lengths of the way between four and five. When readings are obtained from the dials using an apparatus such as that in U.S. Pat. No. 4,007,454 and in accordance with the present invention, they are typically obtained to one decimal place, i.e., in the example just mentioned, in reading the next most significant dial, assuming everything was correct, the reading would be 4.8. In such a situation, the reading which is to be taken from the kilowatts dial would be 4 kilowatt hours, since the tenths dial being at 8 would give the 0.8 kilowatt hours which must be added. Thus, it is the most significant digit of the measured position which is used i.e. the 4 in the example just given. The problem is that it is possible that the next most significant dial, due to a mechanical malfunction, might not be indicating 4.8, but instead might already be at the incorrect readout of 5.0. In this case a reading of 5.8 would be obtained instead of the correct reading of 4.8. 
     In its broadest sense the present invention is intended to correct the dial position of a dial or hand moving between two numbers, e.g., between four and five, such that when moving between these numbers, the sensor is biased such that it detects the hand as always positioned exactly half way therebetween, e.g. at 4.5. This allows for the maximum mechanical error, i.e., plus or minus half of the distance between the two numbers. The most accurate way of doing this would be to apply a continuous correction bias. In other words, as a less significant dial moved through 360°, a continuous correction would be applied to the next most significant dial sensor to maintain its reading at the half way position. For example, if the next most significant dial was moving between four and five, when the less significant dial was at zero, a correction of +0.5 would have to be added. Similarly when the less significant dial was at 0.1, a correction of +0.4 would have to be added and so on. When the less significant dial reached a reading of 0.5, corresponding to 180°, the correction would be zero. When the dial reached six, a correction of -0.1 would have to be applied to bring the next most significant dial back to 4.5. 
     Although the continuous correction is the most accurate, analysis has shown that acceptably accurate results can be accomplished by a quantitizing operation. In this operation, the 360° of the dial is divided in N segments, preferably an odd number of segments. Thus, the 360° can be divided into N=3, 5, 7 etc. segments. For the moment, consider a division into five segments. Each segment or sector would include twice the distance between two adjacent numbers, i.e., there will be a segment between 0 and 2, 2 and 4, 4 and 6 and so on. The correction which is added, in accordance with this embodiment of the present invention, is approximately the average correction for the sector in question. Considering the first sector between 0 and 2. The correction for zero would be 0.5 and the correction for 2 would be 0.3. The average of the two is a correction of 0.4. Thus, in such a situation, if the first dial were at 0 or 1, the correction added would be 0.4. Similarly, between 2 and 4 the correction added would be 0.2. For example, if the dial read 2 or 3 a correction of 0.2 would be added. 
     It has been further discovered that sufficient accuracy can be obtained with a division into only three sectors. Theoretically, the first sector would run from the zero to 3.33. The second sector from 3.33 to 6.66 and the third sector from 6.66 back to zero. The average correction in the first sector would be the average of 0.5 and 0.166 or +0.33. In the second sector the average would be the average of +1.66 and -1.66 or zero. Similarly, in the third sector the average would be -0.133. However, in accordance with the specific embodiment of the present invention which is described in detail herein, this correction is rounded off to 0.3. 
     To illustrate the operation of the present invention, consider the example just given above. Assume that the least significant dial reads 2.3. Only the most significant digit is used and read out. The readout is obtained by counting in a binary coded decimal counter from a zero cross over of a reference sine wave until the zero crossing of the detected signal. The readout of the next dial then commences. However, prior to this readout if the first dial reading was either zero, 1, or 2, 0.3 is preset into the counter. If the reading was 7, 8 or 9, -0.3 is preset into the counter. This is actually done by adding 9.7. The selection of the magnitude and sign of the correction is made by comprison logic. In a manner to be more fully explained below, this, in effect, corrects for a mechanical or linearity error of 3×3.6° or 10.8°. For intermediate values of the dial reading, i.e. 3-6, no correction is made. 
     The same scheme of presetting the correction into a counter can be used for five or more segments. The only difference is that additional comparison logic is needed to generate additional corrections. The manner in which this can be implemented will be obvious to those skilled in the art from the detailed description below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1a and 1b combined are a block diagram of the system of the present invention. 
     FIG. 2 is a diagram of meter dials accompanied by a table, showing operation of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The unit shown on FIGS. 1a and 1b is a unit remotely located at the meter. When reading is not being carried out, the unit simply sits in place with a clock 11 running but not enabled. Operation is initiated from a remote location by placing a signal to ground on line 13 to request an interrogation of the units hand of the meter. This signal fires a one-shot multivibrator 15, the output of which, through an OR gate 17, enables an AND gate 19 to permit the clock to provide its output to the dials. The clock operates at 2.4 mHz which is divided in a &#34;divide-by 6&#34; counter 21 down to 400 KHz. This is divided down again in a &#34;divide by 100&#34; counter 23 to 4 KHz. The 4 KHz signal is filtered in a filter 25 to obtain a sine wave. This is the reference sine wave at 0°. 
     The sine wave at 0° is passed through an RC delay 27 to delay it by 60° to obtain a sine wave at an angle of 300°. The 0° signal is also inverted through an inverter 29 to obtain a signal at 180°. The signal at 300° is inverted through an inverter 31 to obtain a signal at 120°. The 120° signal and the 0° signal are added in an adder 33 to obtain a signal at an angle of 60° and that signal inverted in inverter 35 to obtain a signal at an angle of 240°. In this way six phase signals separated from each other by 60° are generated. These signals are fed to a modulator unit 37 where they are used to modulate the 400 KHz square wave. Thus there are provided as outputs six modulated 400 KHz square waves. These are supplied to the respective segments 39 of the capacitive device associated with the dials, this device being more fully described in the aforementioned U.S. Patent. 
     The 0° signal is also provided to a zero cross over detector 41. The output of the zero cross over detector is coupled through an AND gate 43 to the set input of a flip-flop 44. The gate 43 is enabled by the output of OR gate 17 on line 45 after a delay through a delay means 47 such as a one-shot multivibrator. This delay should be approximately 0.5 milliseconds after the field is applied to the plates 39. The flip-flop output enables an AND gate 49 to couple the 400 KHz signal into a 100 count BCD counter. This counter will be reset by the signal on line 45 coupled through an appropriate one-shot multivibrator 53 or other means to generate a short pulse for reset purposes. The counter counts the pulses until a zero cross over output signal from the hand 55 is detected in a zero cross over detector 57. This resets the flip-flop 44 disabling the gate 49. The number which is stored in the counter 51 thus represents the position of the hand 55. Which of the dials is interrogated is determined by a switch or multiplexer 61 having signal inputs from each of the four hands on the dial and having switching enabling signals obtained from the one-shot multivibrators 15. In the present case, assuming the units are being interrogated the output of the units dial will be provided to the zero cross over detector 57. The output of zero cross over detector 57 resets flip-flop 44, causing gate 49 to be disabled. The output of counter 51 will now represent the meter hand position. This output is stored in a register 62 with the output of the register coupled through drivers 75 which will provide switches closure to ground in BCD output format indicating the dial position which can then be transferred to a remote location. Note that only the most significant digit is taken out of the BCD counter 51. Also note that in the case of the units reading the counter was reset to 0. 
     With reference to FIG. 2, assume that the reading of the least significant dial was 23 in the counter. An output of 2 would result from the register 62. In accordance with the present invention, since this output is less than 3, the counter 51 should now be preset to a count of 3 before the next dial is read. This is accomplished by means of a plurality of gates. The 10 and 20 outputs of the register are provided as inputs to an exclusive OR gate 63. The output of this gate is Anded with the 40 and 80 signals from the register 62 in an AND gate 64. Thus, AND gate 64 will have an output only when the count is 10 or 20. The 10, 20, 40 and 80 signals are Anded in an AND gate 65. This gate will have an output only when the count is 0. Finally, the output of gates 65 and 64 are ORed in an OR gate 66, which will thus have an output only for the counts 10, 20 and 0. Or, in terms of the final output, only for the dial reading 1, 2 and 0. These outputs are one input to two And gates 67 and 68 coupled as preset inputs for the first bits of the units portion of the BCD counter. The second inputs to these gates and to a plurality of remaining gates 69-74, are fed by a common preset signal developed from the one shot 53. Thus, in the example of FIG. 2 where, on the first dial reading the output was 2, a quantity of 3 will be added into the counter 51. This completes the first cycle. 
     The remote equipment will pick up the reading from the drivers 75 and thereafter will provide a signal on line 76 to initiate a reading of the tens. The same process will be followed. With reference to FIG. 2, now assume that 98 counts occur between the time when the flip-flop 44 is set and when it is reset. Since the counter was already at 3 the total count will be 101 and the output will be 0. With a 0 output, the counter 51 will again be preset with the count of 3. Thereafter, an input on line 77 will initiate the 100s reading. Assume that the number of counts here is 93 and with 3 added thereto the count will be 96. The output will thus be 9. With a 9 output, it is desired to subtract 3 from the next count. As indicated above, if the reading is 7, 8 or 9, such subtraction should take place. To accomplish this AND gate 81 and OR gate 83 are provided. Gate 81 has inputs coupled to the 10s output, 20s output and 40 s output and will thus have an output for 70. Gate 83 has as inputs the 80 output and also to the output of gate 81. Thus, there will be an output from gate 83 for the outputs 70, 80 or 90. This is the second input to gates 69-74. Thus, when the preset signal appears, a count of 97 will be loaded into the counter 51. This is equivalent to a subtraction of 3. In other words the first 3 counts after the setting of the flip-flop 44 will return the counter 51 to 0. 
     A signal now appears on the line 79 initiating a reading of the 1000s dial. As shown by FIG. 2 the 1000s dial is slightly past 5. Assume that the number of counts read are 51. From this count 3 is subtracted or 97 is added to give an actual count of 48. With a count of 48 the output which is provided to the register 62 and the driver 75 will be 4. It can be seen that, were it not for the correction, the output would have been 5 and would have been incorrect. 
     Reviewing what has occurred it can be seen that the 10s dial has not quite reached the 0. However, since the units dial just went through 0, now being at 2, the 10s dial should have either just passed 9 or just passed 0. Obviously, there is a mechanical misalignment and the hand should be slightly passed 0 rather than slightly before 0. Through the addition which was carried out prior to reading the 10s dial this error was corrected. In the case of the 100s dial, since the 100s hand is just about to reach 0 the 1000s dial should be slightly before 5. However, due to misalignment it is slightly past 5, i.e., at 5.1. Again through the error correction scheme, by subtracting 0.3, this mechanical error is compensated. The 100s dial has the maximum correctable error. It is shown as being at 93. In actuality, it should be exactly on 9. However, even with this large error the reading obtained is correct. Consider the case where the hand for the 100s dial was exactly on 9. The addition of 3 would do no harm and the output would still be 9. The same is true in the other cases. If the 10s dial was exactly on 0 the addition of 3 would still result in a 0 output. Similarly, if the hand of the 1000s dial was at 4.9 where it should be, the subtraction of 3 would result in 4.6 and the output would still be 4. Thus, it can be seen that the additions and subtractions carried out by the present invention act to correct errors within a reasonable degree while at the same time not introducing errors if the dials happen to be correct.