GB2107046A - Calliper gauge - Google Patents

Abstract

A calliper gauge for internal and external measurements has two relatively movable arms 2,3 which are brought into contact with the object to be measured. The movable arms actuate a measuring mechanism with a shaft of which a rotation proportional to the movement of the arm 3 is transmitted to a display system 13, 14, 18. To make possible a reliable evaluation of the measurement and a high degree of accuracy, and to facilitate the so-called two point measurement, according to the invention the shaft carries an incremental encoder. This produces signals representing in number the shaft rotation. With the encoder is at least one sensor suitable to receive the signals, and the output of the sensor is connected to a signal processing arrangement in which the train of signals is converted into digital signals for a digital display system 31. <IMAGE>

Description

SPECIFICATION Calliper gauge The invention relates to a calliper gauge of the kind which can be made suitable for internal or external measurements, having two arms, movable relatively to one another and which can be brought into contact with objects to be measured, and a measuring mechanism with a shaft driven by one of the movable arms, of which the shaft rotation proportional to the arm movement is transmittable to a display system.

Calliper gauges are known in a multiplicity of variations, so far as concerns the nature of the arms. The arms are made to suit to the type of measurement involved and can have different dimensions, shapes etc. By means of longer and multiply articulated arms, wall thickness can be determined even in inaccessible places such as the bottom of a bottle. By terminating the arms with rollers, the diameter of running threads can be measured. The true measuring part of the device with the measuring mechanism usually has the form of a clock, so that the kind of device referred to is principally known as a dial gauge. In general it is a portable, manually operated gauge.

The measurements can be made on it as two point or three point measurements. In measuring the internal diameter of a hollow cylinder in the form of a tube, for example, the procedure is that the end of one arm is pivoted in a plane radially of the tube; in this way, the maximum deflection is obtained. Then, the end of the arm is pivoted in a plane axially of the tube; in this way the minimum deflection is obtained. Here one is warned that the reading can only be taken when pivoted in both the axial and radial directions. All other intermediate values are of no consequence and cannot be used for the measurement. Details of measurements that can be carried out with calliper gauges are however well-known, so that further discussion here is superfluous.

In the known calliper gauges a pointer is arranged on the shaft of the measuring mechanism, which cooperates with a circular scale. In this way an analogue indication is produced. A high resolution at the pointer is effected by a high transmission ratio. As a rule, on the shaft of the mechanism is also arranged a sleeve, to which a smaller pointer is attached, which indicates, because of a different transmission ratio, scale units to one of two orders of magnitude greater, for example, millimetres. This pointer arrangement can obviously also be retained in gauges according to the invention.

In the prior art, the precision of measurement is however substantially dependent on the skill of the user and the degree of care he takes, to read an analogue display and interpret it correctly. The uncertainty which arises through a misaligned or an eccentric fitting of the dial gauge must clearly be taken into account in the evaluation of the result of the measurement.

The known dial gauges are limited in scope to individual measurements on machine tools, on the shop floor or in the laboratory. Using the known gauges for serial measurements and in statistical quality control is inconceivable, as a repeated cycle of measurement read-off and written noting of the measurement must be established in order to enable the measurements to be evaluated.

The invention is based therefore on the problem of making a calliper gauge of the above described form, which is easier to use, which gives more positive readings and which makes possible more accurate measurements. In particular, the problem of the so-called two point measurement is broadly eliminated, so that the invention results in a broader range of uses.

The invention comprises a cailiper gauge as above described, in which the shaft is associated with an incremental encoder, from which a number of signals proportional to shaft rotation can be generated, the encoder is associated with at least one sensor for the signals, and the output of the sensor is connected to a data processing arrangement in which the output signal is convertible to a digital signal for a digital display.

The invention has the advantage that the measurement, as before, is made in analogue fashion, but the measured value is converted to digital form before it is brought digitally to the display. Because of this conversion, the measured value can be used in all manner of computational operations in the signal processing apparatus, before the result - in digital form - is displayed.

Thus it is for example possible to display only either the maximum or minimum value of a series of measurements, or to find the relationship of the measured values to a tolerance band.

Intermediate values, which it is not necessary to indicate, and which would only confuse the user, need not even reach the display. In multiple error measurements, a display can be set up to display only measured values that are not viable. Further, an automatic zero adjustment can be provided which relieves the user of manual or mechanical adjustment operations.

Furthermore, the digitally displayed value can be transmitted for further processing in an external computer, which is in turn connected to a printer. In such case, the final results can be printed out for statistical purposes.

Erroneous results, which are produced by misalignment or eccentric setting of the mechanism, can be eliminated by a statistical computation by means of a microprocessor in the signal processing apparatus. During the determination of the result, the possible error, subject to the measured values and the program algorithm, will be displayed. As the error tends to zero, the result appears in the display. This remains stored and displayed until switched off.

If a gauge according to the invention should also have the known analogue display with a pointer, the mechanical zero adjustment of the analogue and the digital displays can be brought into coincidence.

It is particularly advantageous, according to a further inventive feature, to make the incremental encoder in the form of a disc, which is arranged on the shaft of the mechanism and has concentric markings for the production of a train of signals.

The disc can be of plastic or metal such as nickel, bronze etc. In particularly advantageous manner, the markings comprise alternate transparent or translucent and opaque areas of the disc, and at least one sensor is an optical sensor. The transparent areas can advantageously comprise slits or small windows, which, with metal discs, can be made by an etching process.

The disc-form incremental encoder is preferably arranged on the mechanism shaft so as to give the highest transmission ratio, that is to say a relative movment of the arms of two or even one millimetre produces a full rotation. Concentric with the shaft and equidistantly spaced, are arranged 200, 100 or 50 marks or windows, so that one rotation of the disc in conjunction with the, for example, pptoelectronic sensor, produces a signal train of 200, 100 or 50 electrical inpulses.

Optoelectronic sensors are - in themselves known. They comprise a light source and a photoreceiver such as a photodiode, which are connected in a fork-shaped structure which fits over the encoder so that the light source is on the one side and the receiver on the other side, and so that the markings (windows) run between source and receiver and produce thereby a train of light impulses, which the receiver converts into electrical signals having an intensity proportional to the light intensity.

It is naturally possible in other arrangements to make the markings alternately magnetic and nonmagnetic areas of the disc and to use at least one magnetic sensor It is particularly advantageous to have two sensors for the encoder to determine the direction of rotation, of which the spacing in the circumferential direction of the encoder is an integer plus a half of the spacing between two adjacent markings. With optoelectronic sensors, one sensor is then illuminated while the other receives no light. As a result, the two signal trains from the sensor exhibit a phase difference, from which the direction of rotation can be determined in the connected signal processing apparatus. The spacing of the sensors in the circumferential direction has the further advantage that inaccuracies in the division of the encoder do not appear in the result.With an optoelectronic sensor the spacing between light source and photo receiver should for this reason not exceed one millimetre. To focus the light rays and to resolve them, an apertured blind or a vernier are suitable.

On account of the high transmission ratio between the movable arm and the encoder the latter has a substantial moment of inertia. It is thus according to a further inventive feature particularly advantageous to arrange a damping element in the mechanism, and in particular to connect the movable arm with a hydraulic actuating and damping element. Such an element comprises a hydraulic unit which has a feeder and a take-up cylinder.

In particularly advantageous manner, the signal processing apparatus is a microprocessor which is so arranged and connected that the maximum and minimum value or the relationship of a value to a tolerance band can be selected for display as desired. With such a microprocessor, the further advantageous functions already described above can be produced by suitably controlling it as will be apparent to an expert.

If through a delayed actioning of the microprocessor or the sensing system, impulses should be lost, it can be ensured by a suitable control that a corresponding alarm indicator will automatically be shown.

Further the movable arm can be connected to a switch member through which the sensor and/or the signal processing arrangement can be connected to the power supply. In this way it is ensured that no current is consumed when the arm is not loaded. In addition, a timer can be connected to the switch member by which the power supply can be disconnected after a predetermined period when the device has not been used. These measures lead to further energy savings which are of importance when the power supply for the device is a nickel-cadmium or a silver-zinc cell with a duration of some eight hours. The recharging can be effected by a plug-in charger from the mains, for which a charging time from complete discharge of around 12 hours is required.

A microprocessor Series MCS 48 made by the firm National Electric Corporation of Japan is particularly suitable for the invention. The complete electronics are usefully mounted on an aluminium oxide ceramic base plate in thick film technology. As a display, a five position digital display is particularly preferred.

One embodiment of the invention will now be described with reference to Figures 1 to 10.

These shown Figure 1 a lengthwise section through the complete calliper gauge, Figure 2 an under plan view of the gauge shown in Figure 1 in the open position, Figure 3 a perspective view of the gauge of Figures 1 and 2, Figure 4 a block diagram of the signal processing apparatus, Figures 5a to 5f flow charts for the different operating modes of the microprocessor, Figure 6 a plan view of a variant of the gauge of Figures 1 to 3, however without a pointer and with only a digital display system, in which several film switches are included at the edge, Figure 7 a plan view of the display system of Figure 6 to a larger scale and with a simultaneous display of all additional display elements, Figure 8 a cross section through one of the film switches, Figure 9 a partial section through the calliper gauge in the region of the actuating and damping elements, and Figure 10 a further section through the actuating and damping element along the line X-X in Figure 9 to a larger scale.

In Figures 1 to 3 is shown a casing 1 from which project two calliper arms 2 and 3 which are designed for internal measurements in tubes or groove interiors. The arm 2 is fixedly connected to the casing, while the arm 3 is movably supported in the casing by means of a pivot bearing 4. The movable arm 3 is connected to a hydraulic damping element, which damps the pivoting movement and reduced the speed of pivoting.

The end 6 of the movable arm 3 adjacent the pivot bearing 4 transmits its movements in the usual manner to a lay shaft 7, and then by means of a thread 8 of metal, synthetic material or silk, which is wrapped around the lay shaft and is stretched over a fork, not further referenced, at the end of the arm 3, substantially perpendicular to the plane of the drawing of Figure 1. One end of the thread is fastened in an adjustment device 9 which serves to optimise the transmission ratio so that the position of the lay shaft 7 is proportional to the distance between the points 2a and 3a of the calliper arms.

The rotation of the lay shaft 7 is transmitted by a large toothed wheel 10 to a pinion 11 , which is part of a measuring mechanism shaft 12. A pointer 13 is also fastened to this shaft, which runs over a circular scale 14 which is divided into 1/100 mm. On the lay shaft 7 is also fastened a smaller toothed wheel 15, which meshes with a further toothed wheel 16, which is connected to a smaller pointer 1 7 by a sleeve, not referenced, which runs over an inner scale 18, which is divided into millimetres.

For the purpose of supporting the parts described the casing 1 has a bulkhead 1 9 on which also a scale plate bearing the scale 18 is fixed. The scale 14 is however not fixed to the bulkhead 19, but arranged on a scale ring, which is fixedly connected to a transparent scale cover 20, which is rotatably fastened on the upper or front face of the casing 1 for the purpose of adjusting the apparatus.

Operation of the apparatus is effected by a push button 34 which, with the illustrated internal callipers, closes the arms 2 and 3 for the purpose of inserting them into the object to be measured, and opens the arms in the equivalent external callipers.

So far as described in detail, the elements of the gauge are known in the art and require no further explanation. In the further course of the description, however, the realisation of such a device according to the invention will be explained.

Fixed for rotation with the shaft 12 is an incremental encoder 21 in the form of a circular disc of extremely thin metal, which has equally spaced markings 22 concentric with the shaft 12, of which only a small number are shown in Figure 2. The total number of markings 22 is generally specified in the description. In the present case the markings are formed from alternative transparent and opaque areas of the disc, i.e. they are etched in the form of extremely small radial slots or windows in the disc.

In the region of the markings 22 at the periphery of the encoder 21 two optoelectronic sensors 23 are arranged, fixed in a fork-shaped support 24 which fits over the encoder 21 at its edge on both sides (Figure 1). On the basis of the arrangement described, the optoelectric sensors 23 produce two phase-shifted trains of electrical impulses at their output from passage of the markings 22 of the encoder, in which the number of impulses corresponds to the distance between the points 2a and 3a of the arms 2 and 3.

The outputs of the two optoelectronic sensors 23 are connected by leads 25 and 26 to a signal processing arrangement 27, which will be further explained with reference to Figure 4.

In the casing 1, an additional space 28 is provided in which three dry cells are accommodated as power supply 29.

From Figures 1 and 2 it is to be seen that the casing 1 has a projection 30, in which a display system in the form of a digital display is accommodated. With the aid of push buttons 32 and 33, different functions of the gauge are switched on or off. [The push buttons can also be provided in the form of film switches in the region of the display area.] In Figure 4 like parts are given the same reference numerals as in the previous Figures.

There is in any event shown only the part of the gauge required for the electrical signal processing. It comprises the shaft 12, the encoder 21 and the optoelectronic sensors 23. On the side of the encoder 21 opposite the sensors 23, light sources 35 are arranged, which are realised as photodiodes.

Leads go from the sensors 23 to triggers 36 by which the signals can be converted to square wave form. The square wave form is then fed to the signal processing device 27 which comprises the microprocessor above described. An external frequency generator in the form of a quartz oscillator is not separately shown; neither is an arrangement for resetting the counter, which is actuated on switching on the power supply.

As external switch elements, the already described push buttons 32 and 33 are provided as well as a further push button 37, which have the following functions: The push button 32 is a limiting value setter with which a lower and an upper limiting value can be preset. The two limiting values define for example a tolerance range for the measurement of a workpiece. As long as the measured value lies within the tolerance range, the display reads "Good'. If, However, the measured value falls outside the tolerance range, the display then reads "Out". Pressure on the push button sets the digital display to begin counting proceeding from the beginning of the measuring region. As soon as the desired limiting value is attained, the push button 33 is actuated, as a result of which the desired limiting value is stored. The function is also displayed as "set".

A third bush button 37 serves for zeroing after each measurement. At all events, each scale value can be zeroed, so that the gauge then shows only the departure from nominal value.

Multiple leads 38 and 39 run from the signal processing arrangement 27 to the digital display system 31, which has five positions and two decimal positions after the decimal point. The digital display is multiplexed in the usual way, for which the usual driving circuits are used.

A further lead 40 runs from the signal processing arrangement to a serial data port 41.

In Figures 5a to 5f are shown different signal flow charts which are generally self-evident from their captions. Figure 5a represents the so-called main program. A switch-on process defines the start of the main program; the microprocessor receives its start command. The program switch setting can, according to the type of device, result from different connections in the electrical switch circuit There follows a zeroing in which the subject of Figure 3 can be produced for example by actuating the push button 37. Then there follows next a test for whether the program followed is to produce a difference indication, that is to say an indication of a measured value in relation to a reference value. If the answer is 'yes', the program continues as shown in the flow chart of Figure 5d.

If the answer is 'no', then there is a test for whether a range measurement is to be carried out, that is to say whether the measured value lies within a given tolerance range. If the answer is 'yes', then further signal processing is carried out according to the flow chart in Figure 5e. If the answer is 'no', then there is a test for whether a 'two point measurement' should be carried out, that is to say, whether it should be determined if the currently determined measurement passes through a maximum (for example, in the measurement of a tube diameter by pivoting the arm in a plane radially of the tube), or if it passes through a minimum (for example, in the measurement of a tube diameter by pivoting the arm in a plane axially of the tube).If the answer is 'yes', the further signal processing is carried out according to the flow chart of Figure 5f. If the answer is 'no', the measured value is simply fed into the display store. The measured value can for example also be fed back into the flow chart behind the zeroing, in order to be used for example as a reference value.

Figure 5b shows the signal process for the correction of the counter corresponding to the motion of the incremental encoder 21. This correction takes over the microprocessor in the routine for external interrupt. After the start of the program, the counter state is corrected. If an error is detected, "ERR 1" will be put into the display store.

The signal flow chart for the multiplex drive of the display as well as the interrogation of the push buttons is shown in Figure 5c. The corresponding functions take over the program section of the Timer-lnterrupt. The start of this program execution is shown as "TI-Start". The follows the loading of the display store, then an interrogation of the input buttons and finally the re-setting.

Figure 5d shows, as already mentioned, the signal flow chart for carrying out the "difference indication" (Figure 5a). First it asks for the reference level, which can be put in via the keyboard. Then the counter state of the display store is interrogated and the value of the reference level subtracted. The difference can either be returned to the position "1" in the program sequence according to Figure 5a, by means of keyboard instruction, or to the position "5" in the program sequence according to Figure 5d.

Figure 5e shows the program sequence for the case of the "range measurement of Figure 5a.

Input of the range limits is effected from the keyboard. it is first determined if the counter state lies within the range limits. If the answer is "no", then "no GO (reject) appears in the display. If the answer is "yes", then "GO" (acceptable) appears in the display. The output value can either be returned to the position "1" in the program sequence according to Figure 5a, or to the position "6" in the program sequence according to Figure 5e.

Figure 5f finally shows the program sequence for the "two point measurement" according to Figure 5a. It is first determined if the counter state is 'falling' or 'rising'. The signal processing is effected separately according to the type of measurement chosen (either with a minimum or a maximum). In either case it is queried if the hysteresis should be overriden or not. The follows, either the determination of the maximum or the minimum value, depending on the type of measurement used.

Knowledge of the flow charts put the expert in position to set up the block diagram of Fig. 4 in connection with the appropriate microprocessor.

In Figure 6 is shown a calliper gauge with a casing form modified from that of Figures 1 to 3.

In this case the scales and pointers for (supplementary) analogue display are eliminated, and the digital display system 31 is arranged in the centre of the casing 1 in an enlarged format and with additional functions and takes up a considerable portion of the surface. From the casing, a push button 34 extends sideways, which is connected to an actuating and damping element 5, of which more will be said in connection with Figures 9 and 10.

Just about the whole upper face of the casing 1 is provided with a flat recess, of which only one wall 42 is visible. In this recess Is a film system, to be further explained in connection with Figure 8, with film switches which are shown as a total of five external switches 43 to 47. Of the five external switches the switch 43 is a selector for the choice of dimensions "mm" or "inch", the switch 44 is an ON/OFF switch and the switch 45 is a program selector switch for the selection of the different measurement modes "internal", "external", "groove", "absolute measurement", "comparative measurement", "tolerance measurement", and "non-optimised measurement".A further switch 46 is a setting switch for setting comparison values and tolerance limits, and the last switch 47 is a setting switch for the verification of the selected program, the measuring and comparison values as well as the tolerance limits. All the switches are constructed as shown in Figure 8. The switches in question are connected in full analogue manner to the signal processing arrangement 27 as shown in Figure 4 for the external switches 32, 33 and 37.

Of the film arrangement 48 at least the uppermost film is formed to be continuous within the rim 42 and has a transparent window 49 below which is located the digital display system.

In this manner there is provided a completely closed, smooth face, which even in a harsh workshop environment allows no dirt to lodge or penetrate.

In Figure 7 is shown the digital display system 31, as far as it can be seen through the window 49, to a larger scale. From the display of numerals a six place display is provided in the usual way as is familiar with pocket calculators.

Additionally, the display system 31 is provided however with display elements 50 to 53, of which the element 50 is a symbol for the measurement of a bore, the element 52 is a symbol for the measurement of a shaft and the symbols 51 and 53 are symbols for the measurement of a groove or flute.

Furthermore, the display system 31 is provided with additional display elements 54 to 57, which show the measuring program selected at the time. The display elements provide alphabetic information and comprise the display element 54 for absolute measurements, the element 55 for comparative measurements, element 56 for tolerance measurements and element 57 for nonoptimised measurements. It is to be understood that not all the symbols or written information will be shown at the same time; rather the display will show them individually, as for example is seen in Figure 6 for the measurement of a bore in a non optimised measuring program.In this way, a "user's guide" is produced since the chosen methods of measurement are displayed, just as the corresponding measurement and computation program in the computer, so that in use of the calliper gauge, the action to be taken by the user is fully indicated.

From Figure 8, it can be seen that the film system 48 and the film switches formed thereby comprises two films, namely an outer film 54 and an inner film 55 on which contact faces 56 and 57 are arranged. The films 54 and 55 comprise flexible insulating material, while the contact layers 56 and 57 are made in the form of parallel metallic strips, of which the strips of one contact layer run at right angles to those of the other contact layer, as shown in Figure 8. The contact layers are held, when no force is applied, spaced from one another by a spacing film 58, but require a relatively small finger pressure in the direction of the arrow 59 in order to close the switch in question. As already remarked above, the outer film 54 is continuous over the display system 31.

From Figures 9 and 10 it is apparent that the actuating and damping element 5 comprises a push button 34 which is connected to the inner end 6 of the movable arm 3 by a first piston 60, a restrictor 61 and a second piston 62. Positive connection is effected by a return spring 63 which pulls the end of the arm 3 against the second piston 62 (Figure 9). The return spring 63 is connected for this purpose with its one end on a projection 6a of the end of the lever 6 and with its other end to the casing 1. The arm 3 is pivotable about the pivot bearing 4, while the arm 2 is fixedly connected to the casing.

From Figure 10 it is further to be seen that the pistons 60 and 62 are arranged inside a cylinder block 64 in bores 65 and 66, which form a Ushaped fluid channel for an hydraulic medium.

Here, the horizontal of the "U" is formed from the restrictor 61. The hydraulic medium is a viscous liquid with only a very small variation of viscosity with temperature. Preferably, a silicon oil is considered, which is admitted through a filling screw 67. Through the bore of the filling screw 67, a suitable calibrated restrictor can also be inserted. The pistons 60 and 62 are sealed by ring seals 68 and 69 with regard to the bores of the cylinders. The cylinder block 64 is fixed to a part of the wall of the casing 1.

By the described combined actuating and damping element 5, the movable arm 3 can only be moved with a highest velocity which is predetermined by resistance to flow of the restrictor 61 in combination with the viscosity of the hydraulic medium. That holds good not only for the actuating of the push button 34, but also for the working of the return spring 63. In this way it is ensured that the mechanical parts of the gauge are protected from overloading and that also the electrical parts are not fed with too high a frequency of impulses which is proportional to the speed at which the movable arm moves.

Claims (23)

Claims

1. A calliper gauge having two relatively movable measuring arms which can be brought into contact with the object to be measured and a measuirng mechanism with a shaft driven from the movable arm, of which the shaft rotation proportional to the arm movement is transmittable to a display system, comprising an incremental encoder by means of which is produced a number of signals proportional to the shaft rotation, the encoder is provided with at least one sensor receiving its signals, and the sensor output is connected to a signal processing arrangement in which the signal train is convertible into digital signals for a digital display system.

2. A gauge according to claim 1, the encoder comprising a disc which is arranged on the shaft and which has concentric markings for producing a signal train.

3. A gauge according to claim 2, in which the said markings comprise alternate translucent (or transparent) and opaque areas of the dics, and at least one sensor is an optoelectronic sensor.

4. Gauge according to claim 2, in which the said markings comprise alternate magnetic and non-magnetic parts of the disc and at least one sensor is a magnetic sensor.

5. A gauge according to any one of claims 1 to 4, in which an actuating and damping element is connected to the mechanism.

6. A gauge according to claim 5, in which at least one movable arm is connected with an hydraulic actuating and damping element.

7. A gauge according to any one of claims 1 to 6, in which the digital display system is integrated together with the signal processing arrangement in a casing holding the mechanism and a bearing for the arm.

8. A gauge according to any one of claims 1 to 7, in which the casing comprises a projection in which the digital display system is arranged.

9. A gauge according to any one of claims 1 to 8, in which the display system comprises a digital display.

10. A gauge according to any one of claims 1 to 9, in which the signal processing arrangement comprises a microprocessor which is so arranged and connected that a display of the maximum value, the minimum value or, as desired, the optimum value is displayed depending on the type of measurement.

11. A gauge according to any one of claims 1 to 10, in which the incremental encoder has two sensors for detecting the direction of movement, of which the spacing circumferentially of the encoder is a whole number plus a half of the spacing between two adjacent markings.

12. A gauge according to any one of claims 1 to 11, in which a switch member is arranged with at least one movable arm, by which the sensors and the signal processing arrangement are connected to the power supply.

13. A gauge according to claim 12, in which the said switch member is connected to a delay, by which the power supply is switched off after a predetermined duration of non-use of the gauge.

14. A gauge according to any one of claims 1 to 13, in which the signal processing arrangement comprises at least three external switches of which one is a limiting value setter, which starts the running of the digital display from the beginning of the measuring region, of which a second has a SET-function, by which the displayed limiting value in question is stored in the memoryof the microprocessor, and of which the third effects zeroing.

1 5. A gauge according to any one of claims 1 to 14, in which the display system has additional display elements for the type of measurement ("inner", "outer" "groove").

1 6. A gauge according to any one of claims 1 to 15, in which the display system has additional display elements for the measuring program ("absolute", "comparison", "tolerance", "nonoptimising").

1 7. A gauge according to any one of claims 1 to 16, in which the signal processing arrangement has five external switches of which one is a "mm/inch" converter, another is an on/off switch, a third is a program selector switch, a fourth is a setting switch and a fifth is a value setting switch.

18. A gauge according to claim 14 or claim 17, in which the external switches are formed as film switches.

1 9. A gauge according to claim 18, in which the film switches comprise at least two films on which contact layers are arranged, which when there is no pressure on the switch are spaced apart by a spacing film.

20. A gauge according to claim 19, in which the outer film is formed to be continuous over the display system and the film switches are arranged at the edge of the display system.

21. A gauge according to claim 6, in which the actuating and damping element has a push button which is connected by means of a first piston, a restrictor and a second piston to the movable arm, which lies against the second piston under the action of a return spring.

22. A gauge according to claim 21, in which the first and second pistons are arranged in cylinder bores which are arranged in approximate U-form in a common cylinder block and connected by a restrictor, and in which the cylinders move in opposite directions.

23. A gauge according to claim 10, in which the signal processing arrangement has a delay by which the signal processing is delayed by at least about 0.4 seconds with respect to the measurement.