HU213827B - Traffic monitoring equipment - Google Patents

Abstract

Traffic monitoring equipment including traffic speed measuring equipment has a signal validation facility incorporated to enhance reliability of the equipment. This facility permits the monitoring operation, for example speed measurement, to proceed only if the validation is positive, if negative the operation is aborted and/or a warning signal or shutdown is activated. Validation is made of pulse sequence, pulse strength, radio frequency interference, insulation breakdown, cable integrity (where cables are used) and the like.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to traffic control equipment, in particular to measuring the speed of vehicles in traffic. However, in principle, the invention can be applied to any traffic-collecting data collection device under the conditions described below.

As a primary application of the device of the present invention, traffic monitoring devices which include cables or cables laid across a road or other surface and which provide electrical signals are exemplified. As is known, the generation of signals of this kind can be traced back to one or more physical origins, including piezoelectric effect, whether resistive and / or generative piezoelectric effect, but also capacitive or triboelectric effect.

Validation or security checks should be performed to increase reliability, accuracy, and ease of operation of this type of equipment. The use of such equipment to enforce traffic rules has many legal benefits. In general, reliability is less dependent on the operator and more reliable measurements are made by the operator.

The measurement of vehicle speed is based on the fact that the speed can be obtained by dividing the distance and the time needed to travel the distance. The accuracy and reliability of such measurements can be improved by automatic error checking and automatic signal printing, malfunctioning, or malfunctioning by malfunctioning and malfunction indication. Accuracy can be achieved by controlling one or a combination of the factors described below.

A device for a similar purpose is described in U.S. Patent No. 4,368,428, which reads signals from two loops and compares and interpolates them. However, since this device only compares two readings, it does not provide the ability to test a single read validation, with the disadvantage that it does not confirm the validity of each read or measurement.

U.S. Patent No. 4,276,539 discloses another apparatus which does not need to be set to a common level when used with similar systems, and which apparatus is capable of distinguishing whether the change is caused by a vehicle or by environmental conditions. It is also suitable for detecting a stationary vehicle and distinguishing it from a moving vehicle. This apparatus is based on the principle of periodically comparing voltage samples taken from the envelope of the received signal, and the circuit operates when the difference between successive samples exceeds a specified value. However, this known apparatus does not perform validation testing on any of the received signals.

Peter Lingensfelser and Per Tilo, entitled "Schleifendetektoren zum Messen des Strassenverkehrs" (Siemens-Zeitschrift Vol. 44, 1970, IL, IL), discuss in detail aspects of the design of magnetic field loop sensors for urban traffic. The article mentions the need to avoid the dependence of equipment operation on climate or weather, the use of moving mechanical components, and the need for the presence of operating personnel. However, this article does not deal with how to enforce individual signs, nor does it provide tools for doing so. According to the article, both the phase position and the amplitude of an alternating current can be used to measure the presence of vehicles, and the effect of long-term variations in loop inductance and the effect of parking vehicles that have been stopped can be eliminated. An important and highlighted feature of this solution is that it operates reliably over a long period of time, regardless of the inductance and condition of the loop. The article deals specifically with the effect of reinforced concrete surfaces and emphasizes that the result is that it operates at the extreme limits of the efficiency of the measuring equipment. However, this article does not disclose how to perform a validation test on some of the signals received from a vehicle detection device.

The solutions described above can have many faults that cannot be eliminated. As a result, the operation of known equipment is dependent on possible errors due to these causes. These include errors due to cable swap (similarly wrong sequence of signals), inadequate signal amplitudes, errors due to radio frequency or electromagnetic interference of useful signals, false signals, or irregularly timed signals from faulty cables.

There is, therefore, a need for further development, for example, of vehicle speed measurement, where speed is determined by the distribution of distance over time, and how this measurement can be made more accurately and reliably.

To meet this need, we have developed a traffic monitoring device comprising an evaluation unit provided with a computing unit for processing pulses generated by a vehicle passing over a sensor formed by cables, sensor strips or other sensors. It is a feature of the present invention that it comprises a sequence unit which checks the correct sequence of the pulse sequence generated by the vehicle passing through the sensor and compares it with the correct sequence, which is associated with the calculator.

In a preferred embodiment of the device according to the invention, the sequence unit comprises detector-erasable and writable bistable multivibrators to which logic grids containing inverters, ES gates, OR gates are connected, which receive a different order of pulses to receive pulses defined in conjunction with bistable multivibrators forms a generating sequence.

The device may be configured to check the correct sequence of signals from one or more cables and / or sensor systems or other sensors according to the actual configuration of the device. This can provide a guarantee against failures, for example2

EN 213 827 Β ul cables are routed to the surface of the carriageway with appropriate arrangement of sensors or the like, for example, when double-spaced cable pairs are placed over the full width of the road to verify compliance with speed regulations and are improperly connected to the equipment. In this case, the correct sequence of pulses is as follows: First, the first start cable, then the second start cable, then the first stop cable, then the second stop cable, with the first pulse on the other side of the carriageway traveling in opposite directions. pulse from the stop cable, then the first stop cable, then the second start cable, and finally the first start cable. Any other order other than this will be rejected by the device as a result of the validity check feature being used. In this way, speed control is measured by independent timing devices, such as a first gauge, from first start to first stop, independently of a second gauge that measures from second start to second stop, and each front or rear or physical contact with the road surface. in relation to any other vehicle axle. Such cables can also be used with the validation device of the present invention to measure deceleration and acceleration. This order-based validation (disabling in case of failure) can be generalized and extended to the respective arrangement of the desired or required cable or cables and / or sensor systems for magnetic loop sensors and other devices.

Operation of the device according to the invention can also be disabled in the event of other types of errors or malfunctions.

Radio frequency interference monitoring can be performed in the equipment to observe radio interference during and between measurements, and in addition, interference free measurement can be achieved. The cables act as antennas and can also provide a radio frequency signal. The risk of measurement error caused thereby can be eliminated by such radio frequency interference check and validation provided by the validation device according to the invention.

In addition, electromagnetic interference from various sources, such as two-way radios, high-frequency communications, high-voltage cables, or lightning, should be monitored. This can easily be accomplished by radio frequency interference or other electromagnetic interference monitoring equipment, which can be operated during and between measurements to ensure interference-free measurements.

Further validation can be achieved by continuously monitoring the level of insulation resistance between conductors, especially in cables, by monitoring low impedance when it is below a specified threshold. For example, the apparatus memorizes the initial value of the cable impedance and / or sets a required minimum impedance limit to be monitored using impedance measurement and this measurement shows a loss of cable insulation. In this way, gradual or sudden degradation of the cable operating parameters can be monitored, leading to a reduction in insulation resistance, erroneous measurements, decreasing accuracy or reliability. The equipment may be switched off and / or warned in the event of a cable failure exceeding a specified level. It will be appreciated that a decrease in the impedance of the insulating material between the conductors of the cable (whether it is a coaxial cable or, for example, a twin cable) may seriously reduce the magnitude of the signal generated between the conductors, for example by the piezoelectric property of the insulating material. For example, low impedance will result in physical contact between conductors due to mechanical damage to the conductor insulation material. Low impedance can result in moisture and water penetrating the cable, for example in rainy weather, when the outer shielding of the cable has previously been wet and, for example, water is injected into the cable due to mechanical damage or at the end or otherwise. The cable insulation can also be damaged in operating conditions, such as heat, sunlight, mechanical pulses on vehicles, or other usage effects.

The device of the invention may be provided with additional validation capabilities by making it suitable for monitoring signal strength. Thus, each pulse, whether piezoelectric, triboelectric, or both (see, for example, ZA 66/0493) must pass through a minimum signal level in order to be a valid trigger for time pulses.

In the solution of ZA 66/0493, the device comprises a circuit which renders it insensitive to "weak" signals. To accomplish this, each sensor (or cable) is associated with one amplifier that amplifies the received signal. The voltage is cut to a threshold value at a threshold current, and preferably a monostable multivibrator produces a pulse within a given time constant. The amplifier only transmits pulses of the required polarity and is also designed to minimize the sensitivity of the scattered pulses. If a pulse is emitted from the sensor, it can, for example, be output to a Schmidt-trigger circuit after amplification of 400 times, and a cut-off rectangular pulse of 3 V can be obtained after cutting. The time constant of the monostable multivibrator can be about 100 ms. During this time, any sensed or scattered signals to the circuit have no effect.

Thus, signals below a minimum threshold level should be neglected to avoid errors due to slow rise due to signal weakness. The validation capability of the apparatus thus provided serves to prescribe the minimum signal strength that must develop within a certain minimum amount of time from the initial threshold in order to validate the timing. Thus, based on the time curve of the signal, the first pulse (positive or negative) must reach a minimum slope, i.e. the pulse magnitude

EN 213 827 első the first differential quotient must reach a minimum value. For example, for a minimum required signal level, the minimum rise time should be in the order of 1 msec to 20 msec, depending on the application and the characteristics required in different circumstances. As mentioned, this validation test is typically performed on both positive and negative signals, whichever comes first. Reference is made to the teachings of ZA 76/495 in connection with signs starting with a positive or negative value.

The apparatus described in this document is preferably designed to operate independently of the initial polarity of the pulses received from each cable, since it is capable of separating the positive or negative phases of the electronic signals from each cable and then processing them separately. In the process, one phase is inverted and then recombined. The phase separation and reunification unit must include active elements, such as transistors, so that the voltage of the pulse generated during vehicle passage is not significantly reduced.

This phenomenon, as well as the design of an appropriate circuit based on it and suitable for accurate measurements, is described in detail and in the appropriate context. The features described there supplementing the signal strength monitoring or validation feature further increase safety, reliability, and ease of use of the equipment. The apparatus is designed so that if the timing signal is positive, the validation signal must be of the same polarity, that is, positive and, of course, vice versa if the negative signal is caused by the trigger. If an error occurs during this check, the start signal will not be accepted.

In the case of a coaxial cable, the capacity of the cable changes as a result of a failure of the internal fiber or shielding and can thus be used to validate the results obtained. In this case, the device must be designed to monitor for frequency change, phase change, and self frequency change. For example, ringing a cable or detecting a change in capacity by other means is particularly suitable. For each cable, a certain amount of capacity per meter can be detected, and in the event of a break, of course, this capacity changes, which can produce an error signal that indicates a cable failure. In this way, the integrity of the internal conductor and / or coaxial shielding can also be observed and thereby make the operation of the device more reliable regardless of the operator.

The apparatus may further be adapted to detect any false signal that does not match the typical signals generated by a normally operating cable that are actually required to monitor traffic and / or measure speed. Thus, for each signal, the parameters within which the parameters of the relevant signal must fall are determined, and then the parameters of each signal produced by the cable can be compared with the required parameters. If such a false signal occurs, for example more than a specified number, this cable may be identified by a suitable error message displayed on the control equipment.

In the foregoing and other aspects, the apparatus of the present invention can be made "fail safe" by stopping or disabling its operation until an appropriate correction is made, whenever a specified threshold value is exceeded or a specified condition is not met.

The monitoring of the cables described above can be extended to coaxial cables, triaxial cables, shielded cable pairs, or any other cable structure or arrangement. In the foregoing, coaxial cables are referred to by way of example only.

These validation tests and safety measures are particularly applicable to the apparatus described in Z A 81/6666 and ZA 88/2312.

ZA 88/231 discloses a useful cable in which the piezoelectric effect is the most significant, compared to other effects, which is achieved by providing a crystalline piezoelectric material pulverized as a filter into a synthetic polymeric material having piezoelectric properties.

Preferably, two types of coaxial cable are used, in which the insulation between the inner conductor and its concentric outer conductor shows the advantageous electrical effect and the outer conductor protects against noise from external sources. This known device further provides a solution for reducing unwanted interference between cables and noise from surrounding sources.

ZA 81/6666 discloses an apparatus which is not only capable of measuring and controlling speed but is also capable of recording and analyzing other traffic data for other purposes. This specification also describes a solution that can automatically compensate for changes in the inductance of the cables over a long period of time, depending on each installation and other factors.

The invention will now be described in more detail with reference to the examples set forth in the accompanying drawings. In the drawing: Figure 1 is a schematic diagram of the vehicle wheel passing through the sensor cable at various time points and a signal generated by the passage through the cable, Figure 2 is a schematic electrical replacement of piezoelectric sensor cable, Figure 3 is a sensor unit with four sensor cables vehicle side view, Figure 4 is a schematic of a sequence unit for verifying the order of the signals provided by the cables shown in Figure 3, the signal shape and resulting thresholds of relatively weak and normal signals in Figure 5, and validation signals in various wheel positions; A block diagram of a device for processing signals provided by ZA 76/14959 for two sensor cables.

As shown in Figure 1, the wheel 1 of the vehicle rotates in the direction indicated by 2 arrows and moves along an arrow 3

EN 213 827 Β on the surface of roadway 4 on which a piezo-electric shielded sensor cable 5 is laid. Thus, as the wheel 1 moves, it moves to position 1 'when completely over the cable 5 and then to position 1' when it is just leaving the cable 5.

Fig. 6 is a diagram showing the voltage pulse U produced by the piezoelectric sensor cable 5, where the relationship between the pulse size and the positions of the wheel 1 is indicated by lines 7,8 and 9, while the wheel 1 takes different positions along the arrow 3; up. Thus, first, the location of the first contact of the wheel sensor 1 with the cable 5 is indicated by line 7, whereby the pulse at line V _b leaves the line of zero voltage 10. The peak pulse reaches position 1 'as indicated by the line 8 drawn to V _p . The voltage then decreases to 0 at position 1, represented by line 9, where the voltage intersects line 10, indicating value 0. The pulse voltage then changes in a negative direction and shows an overshoot followed by a damping vibration 11. The time T between the moment of first and last contact of the wheel casing with the cable, normally at constant speed, is divided into two parts, namely t | and t _{2 are} period periods where ti = t ₂ and T = t] +1 ₂ . For example, if the wheel rim of the vehicle 1 contacts the road surface at a length of 20 cm, then

At 100 km / h:

Thio ⁼ 0.2 * 3600/100 ⁼ 7.2 msec.

km / h:

T ₂ o = 0.2 * 3600/30 = 24 msec,

For a speed of 160 km / h:

Ti60 ⁼ 0.2 * 3600/160 ⁼ 4.5 msec.

For conventional speed measuring equipment, the cables are spaced parallel to each other on the road in a suitable arrangement and the time between pulses generated by the wheel in the first cable and in the second cable by the wheel on the same vehicle is measured. On this basis, speed is determined by dividing the distance by time:

,, ... distance (meters x 3600) speed (km / h) time (msec)

Figure 2 shows a cable and a replacement image. The concentric cable 12 has a central core 13 which transmits the signal while the outer shield 14 is grounded. The insulating material 17 between the core 13 and the shield 14 generates an output signal in the form of a voltage V _out . The figure also provides a replacement image of a generator-type piezoelectric and / or triboelectric sensor cable.

In the replacement image:

V _g = piezo-triboelectric voltage generator,

R _s = series internal resistance,

C _s = serial capacity,

R _l = leakage resistance,

Cl = cable capacity.

This replacement image is a generic piezoelectric or triboelectric phenomenon that occurs in the insulating material 17 between the core 13 and the shield 14 under mechanical stress.

Figure 3 is a side view of a vehicle that intends to pass through four arrangements comprising A, B, C, D cables.

As shown in Figure 3, the vehicle activating the layout activates the layout elements in the order in which they appear on the road surface. The vehicle shown in Figure 3 will activate these elements in ABCD order, while the vehicle in the opposite direction will activate the arrangement in DCBA order. Consequently, any other order is invalid and will be rejected as described. This sequence check can be implemented as shown in Figure 4.

Figure 4 is a circuit diagram of a sequence unit 54 for verifying the sequence of signals from the cables of Figure 3.

The sequence unit 54 comprises 400 -403 bistable multivibrators of the RS type, each of which is enrolled in its associated threshold 1 application. The inverters 404 are connected to the outputs of the bistable multivibrators 400-403, the AND gates 405 connected directly to the outputs of the bistable multivibrators 400-403 or via the respective inverters 404 and the OR gate 406 connected to the outputs of the AND gates 405. circuit can be evaluated by a conventional method. At the output of OR gate 406, it outputs a signal with an appropriate combination of input signals, the output of which 407 is connected to a traffic computing unit 49. (see Figure 6),

The sequence unit 54 has input lines A, B, C, D connected to the sensors, in this case cables A, B, C, D of Figure 3, and connected to the input input of the bistable multivibrators 400-403. Their wipe inputs are connected via this line to the output of the computing unit 49 indicating the completion of the measurement and preparing for the next measurement, from where they receive a wipe at the start of measurement 5, i.e. when the circuit is ready for signal evaluation or signal analysis.

Output of first 400 bistable multivibrator to first input of first AND gate 405, second and fourth

An input 404 of the inverter and a first input of a fourth AND gate 405; the output of the second bistable multivibrator 401 to the second input and the fifth and sixth inverter inputs 404 of the first ES gates 405 and second 405; a third bistable multivibrator 402 output to a first inverter input 404 and a third

The third input of an ES gate 405; the output of the fourth bistable multivibrator 403 is connected to the third input of the inverter 404 and the third input of the fourth ES gate 405. The output of the first inverter 404 to the third input of the first ES gate 405, the output of the second inverter 404 to the first input of the second AND gate 405, the output of the third inverter 404 to the third input of the second ES gate 405, the fourth and fifth inverters 404 outputs to the first and second inputs of the gate, the output of the sixth inverter 404 is connected to the third input of the fourth AND gate 405.

HU 213 827 Β

The operation of the circuits of the sequence unit 54 of Figure 4 is illustrated in the following table. The table indicates the following logical states:

= write = delete

400 401 402 403 fault 407 the 1 0 0 0 0 b 1 0 1 0 0 c 1 1 1 0 0 d 1 1 1 1 0 e 0 0 0 1 0 f 0 1 0 1 0 g 0 1 1 1 0

Taking into account the practical possibilities, seven combination possibilities are created when the vehicle passes through the cables A, B, C, D in the arrangement shown in Figure 3. These seven combinations are represented by the letters a, b, c, d, e, f, g in the table above. The next four columns in the table assigned to these combinations show the status of the 400-403 bistable multivibrators. Each of the seven options specified validates the display at output 407, which means that there is no sequence error in the fifth column of "error 407" in the table. For any other combination, the status combination of the 400-403 bistable multivibrators shown in the table will cause a malfunction and activate the 407 output diagnostic function.

Indicates that if a combination other than that specified occurs, it produces an error signal at its 407 output, which is interpreted by the evaluation unit described below.

Figure 5 graphically depicts a weak and normal signal, with the resulting threshold signal and the validation signal shown below, in appropriate situations and in accordance with the invention.

Figure 5 is a graph of the upper graph showing the lacquer of the normal pulse signal 18 of the kind shown in Figure 1, which is comparable to a weak signal 18 '. The threshold level is indicated by dashed line 19, the current level is indicated by dashed line 20 and the device according to the invention is set to these levels. Lines 21 and 21 'indicate the start of pulses 18 and 18', lines 22 and 22 'indicate the start of the start signals 23 and 23, respectively, with a delay t _{d from} the start of the signal.

The start of the validation signal 24 is indicated by the moment indicated by line 25. The maximum time available for signal validation is triggered by triggers 23 and 23 ', which are continuous for a specified duration tn, _v . If the validation signal 24 does not occur by the end of these maximum periods 27 and 27 ', the circuit generates a validation error signal 28.

The pulse sequence may be rejected for measurement purposes using the validation error signal 28 as follows:

In the case of a vehicle traveling at 100 km / h in accordance with Figure 1, tj = 3.6 ms and t _d <t, if the received signal is normal and good. However, for a weak signal, tdl'-tl'-3.6 ms (see Figure 5). Based on the corresponding delay t _d ', the above velocity is measured at a distance of 1.5 m (see note below), and the signal strength error does not occur if: from the starter cable (e.g., cable A) and the stop cable (C). cable) receives two unified signals with t _do during the time the first wheel of a vehicle at 100 km / h takes 54 ms to complete the 1.5 m measurement distance.

time = 1.5 m * 3600 = 54 ms (T in Figure 5)

If the start is triggered by the peak of the signal (delayed by 3.6 ms) (t _d ), the maximum time error with the 1 wheel on the starter cable (for example, Cable A) is 3.6 ms, while the stop cable (Cable C) is 1 good signal (delay t _d = 0 ms) triggered by wheel touch as shown in Figure 5% error = 3.6x100%: 54 ms = 6.6%.

As a note, the measuring distance should be less than the minimum wheelbase of the vehicle in order to avoid starting timing by one of the rear wheels which would be stopped by the front wheel of the vehicle.

As shown in Figure 5, the detection of a minimum threshold by polarity check is a very important validation test in the present invention. In Figure 5, the upper graph shows a normal pulse of the kind shown in Figure 1, as compared to a graph of a weaker pulse 18 '. The threshold level set on the device according to the invention is shown by dashed lines 19 and the validation level by dashed lines 20. Start pulse 18 of the graph 21 dashed line 18 pulse start of the graph is the beginning of the dotted line 22 shows the start signal 23 after the delay _d. The validation signal 24 begins at the moment indicated by the dashed line 25. In contrast, in the case of a weak signal, the validation signal is omitted, as shown by the line segment 26 and consequently the measurement stops.

For a vehicle traveling at 100 km / h t = 3.6 msec and t _d less than t for a normal good signal. However, if the signal is weak, tdl = tl-3.6 msec. If you take into account that the measurement distance must be less than the shortest wheelbase of the vehicle and the distance is measured at 1.5 m, to avoid starting the vehicle from the rear axle, the following error may occur when omitting the minimum threshold value: 100 For km / h, the real time is t _r = 1.5x3600 / 100 = 54 msec.

The maximum error may be 3.6 msec if the measurement is started at the peak of the signal (delay 3.6 msec). The measurement is stopped by touching the cable with a good signal and the delay is about 0 (0 msec delay), then the error rate, "3.6x100 error bars = - 6.6%

Minimum threshold validation can be applied based on other criteria, namely, the validation signal must occur within a specified minimum time, such as 1 msec, or with an adjustable delay that is determined after the vehicle speed is determined.

EN 213 827 Β, for example, to 3 msec if the speed is 30 km / h or 0.3 msec at 160 km / h and allows a constant maximum error over the entire speed range (for example, 1% error).

The device is preferably configured so that its operation is not affected by the initial polarity of the pulses from each cable. A suitable electronic processing device is shown in detail in Figure 6.

A triple cable 41 is connected to the electronic processing apparatus of FIG. 6, one of which has a common ground 41, a second power sensor 41b connected to a cable 37, and a third power sensor 41c transmits its signals.

The cable 41 first transmits the signal to the evaluation unit 42 delimited by the dotted line. The evaluation unit 42 includes a phase splitter 43 connected to the sensor cable 36 and a phase splitter 44 which is coupled to the sensor cable 37. Each phase splitter 43 and 44 also includes an amplifier. Apart from amplifying the signal, the impedance adapters 39 and 40 and the phase divider combinations 43 and 44 respectively connect the signal and the sensor cables 36 and 37 to the cable 41. One of the phase divider combinations 43 and 44 is connected to an inverter 45 which performs an inversion operation in the present. The signals are then applied to a gate unit 46 and connected to one of the trigger inputs and the other to the stop input. In addition, a gate oscillator 47 is coupled to the input of the gate unit 46, which outputs a relatively large 2 MHz signal to achieve a small gating error. The gated signal then carries the measured time and is connected to 48 counters through frequency divider 53. The frequency divider 53 divides the frequency of the gated signal to 10 kHz. The value obtained from the counting of the divided signal is then connected to 49 computing units. The calculating unit 49 performs the necessary operations on the value bearing the result of the time measurement and calculates the speed value relative to the distance between the sensor cables 36 and 37. The validation input of the computing unit 49 is further coupled to the sequence unit 54, the input of which is indirectly connected to the cables A ... C. The calculating unit 49 will only produce results if the ordering unit 54 finds the detection order to be correct. The measured speed value is connected from the computer 49 to the decoder 50, from where it is connected to a display 51 as a decimal value and, if desired, to a storage display 52. The measured speed value can be displayed in either km / h, mile / h or other desired units.

Claims (2)

PATENT CLAIMS A traffic monitoring device, comprising a unit for evaluating a pulse generated by a vehicle passing through a sensor formed by cables, sensor strips, or other sensors, characterized in that a sequence of pulses generated by a vehicle passing through the sensor is verified and ordered in the correct order comprising a unit (54) communicating with the computing unit (49). A traffic control device according to claim 1, characterized in that the sequence unit (54) comprises erasable and writable bistable multivibrators (400-403) connected to their sensors inputs, the outputs of which on inverters (404) and AND gates (405). connected via an OR gate (406) whose output (407) is connected to the validation input of the computing unit (49), and the bistable multivibrators (400-403) are connected to the computing unit (49) by a wipe input.