MEASURING INSTRUMENT PROVIDED WITH ANALOG AND DIGITAL DISPLAY

Abstract: A display for a measuring instrument comprises an array of liquid crystal display segments (14-16) forming a scale and a multi-digit numerical display (18) in which each digit position comprises a multi-segment liquid crystal display. An input cir­ cuit comprises a transducer (32), which may be responsive to mechanical, electrical or any other form of signal, and an ana­ log-to-digital converter (36) to provide digitised input signals. Under the control of a signal processing circuit (38) which may use a microprocessor, the digitised signals are applied to re­ spective decoder/drivers (40, 40a) for the scale array and numerical display such that the scale is stepped by one seg­ ment for each unit change in the next to least significant digit (18b) of the numerical display. The least significant digit there­ by provides an interpolation of the input value between adja­ cent segments of the scale array which provides a stepped or quasi-analog display. The display may also provide limit annun­ ciators (24, 26) driven by comparator means (42, 43; 44, 45) re­ sponsive to the current digital values.

Description: Title: Analog and Digital DisDlay Device This invention relates to a display device and is concerned with a device providing a display both in the form of a scale and numerically (digitally). A particular, thoagh not exclusive, application of the invention is the provision of a display for a measuring instrument, for example a gauge. There is in the prior art a number of devices which digitally indicates measurements as, for example, a micrometer of the kind disclosed in United States Patent Specification 3,924,336 and height gauges as disclosed in United States Patent Specifications 3,924,337 and 4,037,325. Devices such as this are satisfactory when a fixed part is to be measured but may not be satisfactory when a part being measured is moving with respect to the gauge so that the decimal numerals are changing to rapidly to be followed by the eye. This forces the operator to slow the machinery down to a point where he can make a visual indication with some accuracy and/or see the measurement variation that is occurring. The present invention enables us to provide a display device for a measuring instrument in which a value is displayed on a quasi-analog scale simultaneously with its display in numerical form to a higher degree of accuracy whereby the analog scale is interpolated. The analog scale enables variations to be better seen by the operation: the numerical scale enables values to be read out with accuracy. There are a number of devices in the prior art that provide visible displays in both analog and digital form which are representative of various phenomena. For example, there are prior art devices that will display time, such as that suggested in United States Patent 3,772,874. This device is purely showing time generated from a clock source. United States Patent 3,696,385 discloses a digital readout of values corresponding to those on a conventional rotatable mechanical scale. Broadly stated, according to one aspect of the present invention there is provided a display device comprising: a viewable display face; an array of liq#uid crystal display segments supported on said face in the form of a scale; a numeric display comprising a plurality of digit displays in line, each digit display comprising a multi-segment liquid crystal display supported on said face and selectively operable to show numbers; and an electronic circuit for activating said array and numeric display comprising: an analogue-to-digital converter for receiving an analog input signal for conversion to digital form; first decoder/driver means connected to selectively activate said array in response to the digital form signal so as to activate a segment of said scale in accord with the value of the input signal; second decoder/driver means connected to selectively activate said numeric display in accord with the value of the input signal; and the operation of the said first and second decoder/driver means being related with respect to the values displayed such that an increment of one segment of the array scale equates to a unit change of number in the second least significant digit of the numeric display whereby the least significant digit provides an interpolation of values lying between adjacent scale segments. One preferred form of scale is to have the arrangement in a circle. The numeric display is then located within the circle. It is also preferred that the numeric display has at least three digits. In another aspect of the invention there is provided a measuring instrument comprising: an input transducer for providing an analog electrical signal representative of an input quantity; and a display device that comprises: a viewable display face; an array of liquid crystal display segments supported on said face in the form of a scale; a numeric display comprising a plurality of digit displays in line, each digit display comprising a multi-segment liquid crystal display supported on said face and selectively operable to show numbers; and an electronic circuit for activating said array and numeric display comprising: an analog-to-digital converter responsive to the analog electrical signal from said transducer to convert said analog signal to digital form; first decoder/driver means connected to selectively activate said array in response to the digital form signal so as to activate a segment of said scale in accord with the value of the input signal; second decoder/driver means connected to selectively activate said numeric display in accord with the value of the input signal; and the operation of the said first and second decoder/driver means being related with respect to the values displayed such that an increment of one segment of the array scale equates to a unit change of number in the second least significant digit of the numeric display whereby the least significant digit provides an interpolation of values lying between adjacent scale segments. The display device in such a measuring instrument may be provided with a further display segment set in the viewable face, and comparator means connected to activate the further segment and responsive to the digital form signal to cause the further segment to display when a preset limit is equalled or exceeded. More particularly, this arrangement can be duplicated to detect and display signal excursions beyond defined upper and lower limits. For convenience in use, additional display segments may be provided such as a low battery indicator segment or segments. Through the use of the electronic circuitry associated with the device, the least significant digit in the numerical display serves as a vernier in interpolating between analog segments. In the measuring instrument the transducer may have a mechanical displacement as the input quantity, for example by being provided with a movable measuring stem which contacts a part being measured. In other uses the transducer may be coupled to an electrical line to respond to an electrical input quantity. In both cases the transducer produces an electrical analog signal which analog signal is then converted by an analog-to-digital converter. The invention and its practice will be further described in relation to a measuring gauge instrument embodying the invention and illustrated in the accompanying drawings, in which: Figure 1 is a perspective view illustrating the measuring gauge instrument in one practical application; Figure 2 is a perspective view illustrating the instrument in another application; Figure 3 is an enlarged, more detailed, view of the display face of the instrument; Figure 4 is a block schematic diagram of the circuitry of the display device whose face is seen in Figure 3; and Figure 5 is a block diagram illustrating an alternative transducer for the circuit of Figure 3. For the purposes of illustration, the invention is shown embodied in measurement systems for machine parts. In the system of Figure 1 there is illustrated a gauging station which is known, for example, as a comparator and which includes a ground base 60 with a vertical column 61 rising from the base. On the column 61 is a mounting attachment 62 to which the case 10 of the measuring instrument is attached. As will be seen by referring to the drawing, the instrument has a displaceable measuring stem 30 that is engaging a workpiece W which lies on the ground base 60 and may be rolled thereon to give a measurement as the measuring stem 30 engages the periphery thereof. In the system of Figure 2 a gauging station is shown in use on a rotating part on a lathe or a similar machine which includes a bed 70. As is usual in a rotating tool machine there is rising from the bed a fixture such as 71 that carries a center point such as 72 or the like, a chuck (not shown) being used to drive the rotating machine part here illustrated as W'. On the bed 70 there is mounted a base 74 which may be of the permanent mallet type that carries an upright post 76 and like the illustration in Figure 1 there is an attachment member 77 which carries the instrument case 10. Referring now to Figure 3 contained within the case 10 of the instrument is electronic circuitry as well as display segments selectively driven by the circuitry and which are supported on a display face of a suitable material such as glass or the like as well known to those skilled in the art. The display face which is viewable through a window 12 of the case comprises an array of, for example, one hundred and one segments circularly arranged in a scale to indicate dial divisions. For ease in illustration one segment 14 is shown in the visible state while two segments 15 and 16 are shown in broken lines to indicate non-illuminated or non-visible segments. It will be of course understood as well known to those skilled in the art that each of the segments is connected to an electrical lead so that it may be appropriately energized by electronic driver circuitry. Representative scale indicia are provided for the array segments which may indicate some form of measurement either in thousandths of an inch, tenths of an inch, appropriate metric system units, volts, millivolts, milliamps, grams, or whatever units corresponding to the variable being measured, and accordingly suitable digits and scale divisions as seen in Figure 3 are provided. It will be seen from the Figure that the scale segments 14-16 and so on are formed as pointers to the marked scale indicia. Thus measurements indicated on this scale are incremental or stepped without any interpolation between next adJacent segments. This is what has been called above a quasi-analog display and may also be referred to in the illustrated form as a pointer-type display. The segments could be alternatively all activated up to the value to be indicated in the manner of a bar graph. Various scale layouts are possible. Within the central area of the circularly arranged segments there is provided a multi-digit numerical display comprising a line of digit indicators each comprising groups of segments selectively operable to display a required number as, for example, seven individual segments for each digit position. There are illustrated and generally indicated at 18 five such digital display areas, two of which are indicated as 18a and 18b. In addition, there are provided at least three decimal point segments as, for example, the decimal point indicated by the reference numeral 20 and two further sets of segments 22 and 23 which will indicate a direction or polarity in the form of a plus or a minus as the case might be. For certain purposes it is desirable to provide means which will indicate when a part is within a given tolerance. It is appropriate to be able to put into and store in the instrument an upper limit of measurement as well as a lower limit of measurement and when these are reached or exceeded, annunciator segments such as segments 24 and 26 can be illuminated. Additionally, since the illustrated instrument is of a portable nature, it is battery powered and segments such as 28 are provided to display the symbol of a battery indicating to the user that the battery needs to be replaced. It will be understood, of course, that the segments and the input leads thereto maybe formed on the suitable support layer by a variety of methods such as sputtering, evaporation, photo masking or etching and the segments may be made of a suitable transparent electricallyconductive reflective or transparent material depending upon whether the display is operated in a reflective or transmissive mode, all as well known to those skilled in the visible binary segment display art, including such devices as light-emitting diodes, liquid crystals, gas discharge tubes, plasma displays, and so forth. More particularly the display uses liquid crystal display (LCD) segments to form both the numerical display and the analog scale. The scale segments are individual LGD elements. Each digit position is a multi-segment LCD display selectively operable to show numbers. The display shown in Figure 3, which is a combination analog display and a digital display, has been particularly structured to provide a display for a distance measuring device, which is generally known in the art as a dial indicator. Dial indicators have long been known in the measuring art and are exemplified as, for example, by U.S. patent 2,484,770. Basically, they have been used to ascertain the value of a variation from a standard or they might be used to measure the eccentricity of a rotating part, such as a part which is being trued in a lathe. The analog display is necessary to search for high and low points in such a situation. These prior art devices are mechanical devices in which magnification is obtained with gears and accuracy is necessarily limited and is a direct result of tolerance in the mechanical parts. By using an electrical method, there is only one moving part and there is no gear nor bearing wear resulting in error as in the prior devices. Further, the resistance to shock is excellent. Accordingly, the present instrument utilizes an input transducer, and in the mechanical distance measuring version has the measuring stem 30 which is coupled directly to the transducer. Referring now to Figure 4, there is shown a part 31 which is being measured for tolerance or eccentricity for example as mentioned above. The part is contacted by the displaceable measuring stem 30 (Figure 3) whose movement is communicated to a transducer 32. The transducer 32 may take a variety of forms but it is preferred to utilize a differential transformer which is well known in the art as consisting of a primary coil, a pair of secondary coils and a core member which is carried by the movable member or measuring stem 30. The primary coil of a differential transformer system is, as well known to those skilled in the art, energized by an oscillator which energizes the primary coil at a frequency say of 5 kHz. The outputs of the secondary coils develop a differential voltage or other analog signal such as a variable inductance that varies as a function of the position of the core member relative to the secondary coils, and this analog signal is then passed through a suitable amplifying transducer interface 34 and thence to an analog-to-digital converter 36 which, for example, could be a type LD131 made by Siliconix. This converter generates signals in a coded form representative of the instantaneous amplitude or frequency of the analog signal being evaluated. The signals are then provided to an electronic circuit 38 consisting of logic gates interconnected in a certain prescribed manner enabling their use for carrying out such operations as digital signal comparisoni counting, bit incrementing and decrementing and signal power amplification. The circuit 38 can be realised with the aid of a microprocessor device programmed to perform the functions stated. The circuitry is also designed to accept inputs from switches manually actuated to alter the circuits function. An additional function of the circuit is to provide electrical signal outputs to external computers, signal processors, process control systems, statistical analyzers and the like. The signal processing circuit 38 may include a memory location which will be loaded with the contents of a bus 39 when the zero switch 37 is activated. This number will be subtracted from future readings. An increment switch 50 will cause this stored number to increase at the rate of approximately three numbers per second as long as the switch is held closed. A decrement switch 51 will cause this stored number to decrease at the rate of approximately three numbers per second as long as the switch is held closed. The bus 39 provides communication between the circuit 38 and a number of other circuits comprising decoder/driver 40, a decoder/ driver 40a, a limit one latch 42, a limit two latch 44, and also a comparator 43 and a comparator 45. Decoder/driver 40 provides sufficient voltage for driving the segments of the digit indicators of the digital display 18 and is responsive to a binary coded input from bus 39. Decoder/driver 40a is also responsive to a binary-coded input, which may be the same input as for unit 40, from bus 39 and will drive up to 101 segments of the so-called pointer display as seen generally in Figure 3. The operational relationship between the decoder/drivers is such that in the decoder/driver 40a for the scale segments steps the indication one segment for each unit change in the decimal numerical value of the next to least significant digit 18b of the numerical display. Thus, when the digit 18b reaches zero effectively it will be accompanied by an incrementing or decrementing of the analog scale by one causing a different position to illuminate adjacent to the previously illuminated position. For example, by referring to the drawing, if the digit 18b increments by "one" and assuming that 15 was illuminated, then 16 will become illuminated at the time of the increment. The decoder/driver 40, however, is working to a finer degree of resolution in driving the fifth, least significant digit of the display and thereby provides an interpolation of the analog display scale or, for example, a grad splitter. As seen in Figure 3 by way of example, it will be noticed that the analog display shows by illuminated position 14 the digit 9, while the digital display shows 0.00093, the last digit being effectively the fifth decimal digit represented on bus 39 to which the decoder/driver 40 is responsive, and of course, indicates that the actual position as seen by the transducer 32 is three-tenths of the way between 9 and 10. Limit latch 42 is used to store a reading by pressing button 53, and it can be readily seen by referring to the drawing that the reading is stored in latch 42 and is compared with the reading currently found on the bus 39 by the comparator 43. The comparator will energise an annunciator such as 24 as seen in Figure 3 on the display to indicate when the bus value equals or exceeds in one direction the limit stored in latch 42. A similar operation occurs for limit latch 44 on the drawings, and this can store a different reading in an opposite direction by pressing button 54, and when its comparator 45 senses the equalling or exceeding in the opposite direction of that reading, then it will pulse the other annuniciator 26. Thus excursion beyond set high and low limits are indicated. For convenience of operation a low battery sensor 48 may be provided which will be sensitive to the battery voltage, and if the battery voltage drops below a preset level will pulse the display segments 28 and shut down the rest of the system. Referring to Figure 5 an alternate transducer 32a is illustrated as coupled to electric lines 31a, the transducer 32a being sensitive, for example, to voltage current or resistance or any other electrical parameter desired. For example, one can conceive of a situation in which the electrical transducer 32a could also be sensitive to pressure, could indicate force in the form of a strain gauge or temperature, and divers other applications. In this embodiment, the disadvantages of the slow response of usual analog meters, due in large measure to the ballistics of the movement, are avoided and, for example, the tuning of resonant circuits may be easily facilitated.

Claims: Claims: 1. A display device comprising: a viewable display face; an array of liquid crystal display segments supported on said face in the form of a scale; a numeric display comprising a plurality of digit displays in line, each digit display comprising a multi-segment liquid crystal display supported on said face and selectively operable to show numbers; and an electronic circuit for activating said array and numeric display comprising: an analog-to-digital converter for receiving an analog input signal for conversion to digital form; first decoder/driver means connected to selectively activate said array in response to the digital form signal so as to activate a segment of said scale in accord with the value of the input signal; second decoder/driver means connected to selectively activate said numeric display in accord with the value of the input signal; and the operation of the said first and second decoder/ driver means being related with respect to the values displayed such that an increment of one segment of the array scale equates to a unit change of number in the second least significant digit of the numeric display whereby the least significant digit provides an interpolation of values lying between adjacent scale segments. 2. A display device as claimed in Claim 1, in which said scale array is arranged in a circle and said numeric display is located within the circle. 3. A measuring instrument comprising: an input transducer for providing an analog electrical signal representative of an input quantity; and a display device that comprises: a viewable display face; an array of liquid crystal display segments supported on said face in the form of a scale; a numeric display comprising a plurality of digit displays in line, each digit display comprising a multi-segment liquid crystal display supported on said face and selectively operable to show numbers; and an electronic circuit for activating said array and numeric display comprising: an analog-to-digital converter responsive to the analog electrical signal from said transducer to convert said analog signal to digital form; first decoder/driver means connected to selectively activate said array in response to the digital form signal so as to activate a segment of said scale in accord with the value of the input signal; second decoder/driver means connected to selectively activate said numeric display in accord with the value of the input signal; and the operation of the said first and second decoder/driver means being related with respect to the values displayed such that an increment of one segment of the array scale equates to a unit change of number in the second least significant digit of the numeric display whereby the least significant digit provides an interpolation of values lying between adjacent scale segments. 4. A measuring instrument as claimed in Claim 3 in which said display device comprises a further display segment set in said face, and comparator means connected to activate said further segment and responsive to said digital form signal to cause said further segment to display when a preset limit is equalled or exceeded.

Inventors: CLARK, EARL S.
Applicants: FEDERAL PRODUCTS CORPORATION
Application year: 1980
Main classification: G01R13
IPC codes: G01R13, G01D7