DE2320391B2 - Device for weighing moving loads - Google Patents

Description

number of pulses by interposing a frequency divider (15) with a fixed division factor of one Counter (6) detected and depending on the counter reading via a memory (18) in a second Frequency divider (19). via which the pulses are fed to the counter (6) during the back integration time the number of pulses at which a pulse is passed on is marked.

8. Apparatus according to claim 6, characterized in that that ring counters are used as frequency divider with a fixed setting or can be marked via a memory.

9. Apparatus according to claim 5, characterized in that the fundamental oscillation of the pendulum load is fed to an ÄC element, and the voltage (la) and a voltage (Ub) phase-shifted by the capacitor (Q ) is fed to a comparator (27) whose Output voltage flips over at each maximum and minimum and these breakover voltages are used to switch the measuring time of the digital voltmeter.

10. The device according to claim 4, characterized in that a first contact (M 3) and a second contact (MA) are arranged at twice the distance of the measuring section on the weighing bridge in front of the measuring section and a second contact (MA) through the first Contact a constant frequency is switched to a counter for summation and the second contact stores the counter reading and at the same time the constant frequency is switched on for subtraction and the measuring time is switched on when the zero value is reached and the measuring time is ended when the negative value of the stored counter reading is reached .

11. The device according to claim 10, characterized in that that at the beginning of the measuring time the counter is set to the stored count and is counted back to zero by the incoming pulses and when the value is reached zero the measuring time is ended.

The invention relates to a device for weighing moving loads, whose load cells act on at least one load cell exerted force results in a time-varying electrical voltage curve with a digital voltmeter according to the principle of double integration, in which first a voltage to be measured and then a reference voltage of reversed polarity at an integrator with a downstream comparator (Threshold switch) are switched on and the back integration time to the initial value is measured by the number of pulses at a constant frequency, is a measure of the voltage to be measured.

For weighing moving boxes that swing, for example, on a crane hook or using one as a weighing bridge designed road section is driven, for example, from the brochure »Digital DMS measuring device, type GV 03 «from the company Keller Spezialtechnik GmbH, an arrangement is known in which during a constant period of time given by the constant integration time of the digital voltmeter is, this is supplied with the output voltage of the load cell. The constant time base is used formed with the help of a counter that counts the pulses

of an oscillator summed up to a certain count. The output voltage of the integrator then reaches a certain value, which is dependent on the output voltage of the load cell. At the end of <Jer integration period, a constant reference voltage of opposite polarity is connected to the input of the integrator and the counter is set to zero.During the discharge time of a capacitor of the integrator, the counter bu adds up the oscillator pulses to a certain value of the output voltage of the integrator. The counter reading for this point in time is proportional to the voltage to be measured and, with suitable calibration, represents a value for the weight to be determined.

A particular difficulty is that the fixed integration time determined by the digital voltmeter is given, does not optimally correspond to the conditions in the sequence of movements of the loads. To get one as possible To enable accurate measurement, one strives to get an average value of the changing voltage to be formed in a period of time that is particularly suitable for this. For example, one should have a weighing platform moving load, the integration time should be selected to be as long as possible in order to be representative To obtain mean value, on the other hand, should periods of time in which with a falsifying the mean value formation Voltage curve must be expected, be excluded with certainty, z. B. should the voltage peaks occurring when driving onto a weighing platform are not taken into account.

Furthermore, from US-PS 36 74 097 a movement indicator known for a pressure lock of a balance. The weight displayed is continuously being used corresponding pulse trains are counted and stored. The number determined in each case is compared with the previously determined number compared and only if the result of this comparison is a given several times in a row If the value falls below this, the printing process for the scales is triggered. This ensures that There is no change in the pending number during the printing process. However, this arrangement is unsuitable for determining a weight.

The object of the invention is to design a weighing device of the type mentioned at the outset in such a way that the Weight of moved loads with great accuracy while adapting the integration time to the requirements the sequence of movements of the load or the force profile can be determined.

This object is achieved according to the invention in that the beginning and end of the measuring time are dependent from the sequence of movements of the load or the force curve can be determined by switching means that the memory center store a value proportional to the variable measuring time and that the re-integration time serving as the measuring time can be corrected via a switching device as a function of the stored value. Included the integration time, i. H. the measuring time can be optimally adapted to the sequence of movements, since the start of the measurement and in particular the end of the measurement process can be placed in such a way that, on the one hand, fco the largest possible measuring time is available that but on the other hand falsifying influences remain excluded. This adaptation to the circumstances of the respective movement sequence can take place separately for each individual measuring process without <> s this requires changes in the measuring arrangement.

A particularly high accuracy of the measurement is achieved by the fact that the measurement time is proportional The value is stored digitally in the form of a number of pulses in a memory and the one used as the measured value Back integration time digital in a multiplication component multiplied by the quotient of the normal number of pulses and the number of pulses stored for the measuring time will.

The digital correction of the reintegration time can be interposed in a further training a frequency divider, which is in the ratio of the normal number of pulses to the stored number of pulses is preset for the measuring time

The cost of construction is particularly low if the concept of the invention is further developed the value proportional to the measuring time is stored in a memory analog as an integral value of the reference voltage and the back integration time serving as the measured value is analogous to that which is dependent on the measuring time Corrected the integral value of the reference voltage and the resulting steepness of the back integration will.

If the weighing device has a weighing platform over which the load travels, for. B. freight wagons in a further development of the concept of the invention, the beginning and end of the measuring time expediently by two of the load when driving onto the weighing platform and when leaving the weighing platform, the actuated switches are determined. This means that regardless of the speed of the load being moved, the largest available in each case standing, but still undisturbed measuring time utilized.

In yet another inventive embodiment, the beginning and end of the measuring time are determined by two oscillation maxima and minima, respectively, for loads swinging to the carriage, for example on crane hooks. This increases the accuracy of the mean value formation compared to a constant or arbitrarily selected measuring time. A device for determining the beginning and end of the measuring time as a function of two oscillation maxima or minima is, according to a further feature, that the fundamental oscillation of the oscillating load is fed to an RC element, and the voltage fed in is fed to a comparator which is phase-shifted by the capacitor whose output voltage changes over at every maximum and minimum and these breakover voltages are used to switch the measuring time of the digital voltmeter.

If it is not possible to arrange switching contacts on the weighing platform itself, through which the measuring time and is switched off, this can be done according to a further feature in that at twice the distance the measuring section on the weighing platform in front of this measuring section a first contact and at a single distance a second contact is arranged in front of the weighing section and a constant one due to the first contact Frequency switched to a counter for summation and stored by the second counter reading and at the same time the constant frequency for the sub-action is switched on and when the zero value is reached the measuring time is switched on and when the negative value of the stored counter reading is reached, the Measuring time is ended.

The subject matter according to the invention is based on the following description of exemplary embodiments and the schematic drawings. It shows

F i g. I a schematic representation of a weighing bridge

ke over which the load to be determined travels, with a schematic representation of the electrical Load cells,

F i g. 2 shows the course of the output voltage in FIG. 1 shown load cells as a function from the time,

F i g. 3 shows the course of the output voltage of a load cell which is acted upon by a pendulous load will,

F i g. 4 shows a block diagram of a measuring device with a digital voltmeter for determining the weight by means of a load cell,

F i g. 5 shows, in a simplified representation, an embodiment for a start-stop device in FIG. 4,

F i g. 6a, 6b voltage curves over time, which in the circuit according to FIG. 5 result. F i g. 7 is a block diagram of an embodiment for the digital voltmeter in Fig. 4, the storage of the value proportional to the measuring time takes place digitally,

F i g. 8 is a diagram of the voltage curve in the digital voltmeter according to FIG. 7,

F i g. Figure 9 is a block diagram of another embodiment of a digital voltmeter for the circuit according to FIG. 4, whereby the storage of the value proportional to the measuring time takes place analogously.

F i g. 10 is a diagram of the voltage profile over time for the digital voltmeter according to FIG. 9,

F i g. 11 shows the circuit of a modified embodiment a digital voltmeter according to the invention and

F i g. 12 shows a diagram of the voltage profile over time in a digital voltmeter according to FIG. 11th

In the case of the in FIG. 1, a weighing bridge 22 is arranged in the path of movement of a load 21 moved at the speed ν. It can, for example, be a weighbridge over which a railroad car to be weighed rolls at an approximately constant speed. their circuit in FIG. 1 is indicated schematically. The output voltage Ua of the load cells 23, which is proportional to the applied force F, shows, for example, a time curve as shown in FIG. 2 is shown over time f.

On the weighing platform 22 there are locally adjustable signal contacts Ml and M 2, which, for example, act as contact thresholds. Light barriers or the like can be executed and give a signal when they are run over by the load 21. As one can see from FIG. 2 recognizes it is assumed in the example shown that at a limited speed ν of the moving load 21 the collision impacts have subsided when the first signaling contact M 1 is reached and the mean value of the vibrations occurring due to the movement of the load corresponds to the weight of the load Contact M1 initiates the measurement and closes the second signal contact M 2. The evaluation and display is carried out by the digital voltmeter after the moving load has released the MeWekontakt M2. This gives an optimal measuring time, as can be seen from FIG. 2 recognizes

If the arrangement of signal contacts M 1 and M 2 on the weighing platform 22 is not possible. werdea said Koen contacts NEN even before the weighing platform arranged in the track Such brought forward Mekjekontak te M 3 and MA are in g F i. 1 also shown. With the contact M3 could then z. B. Let a counter be started that adds up the pulses of a constant frequency. This counter is stopped by the signal contact M4. The counter reading is saved and corresponds to the speed of the load. After the signal contact M 4 has been released, the counter counts down until the value zero is reached. If the speed ν of the load being moved remains constant, which can be assumed for this relatively short distance in most applications, then the load is at position 21 when the count is zero, ie on the weighing platform. At this point in time, the counter can be reset to a value that corresponds to the saved count. However, the counter can also continue to record the incoming pulses until its reading corresponds to the negative value of the stored counter reading. Simultaneously with the further summation of the pulses, the integration of the measuring voltage begins. If the counter reading is zero or if the stored counter reading is negative, point 31 is reached. The integration is ended. The evaluation is also carried out by the digital voltmeter.

In Fig. 3 is the voltage curve at the output of the load cell with a swaying load z. B. at a Crane scale shown. One recognizes the fundamental wave of the vibrations with the superimposed harmonics. In order to achieve a particularly good averaging of the voltage curve, several complete Oscillations of the fundamental wave are averaged, whereby the measuring voltage is determined by the digital voltmeter is integrated. In order to measure over several complete oscillations, from maximum measured to maximum or minimum to minimum.

F i g. 4 shows the circuit of the measuring device in a greatly simplified representation. The load cell 23, on which the force F acts with fluctuations Δ F , is supplied by a power supply unit 24. The output of the load cell 23 is connected to a start-stop device or a trigger device and a digital voltmeter controlled by them. F i g. 5 shows the circuit diagram of the trigger device or the start-stop device of the block circuit according to FIG. 4. In the unit 25, which consists of an amplifier and an active filter, the output signal of the load cell 23 is amplified and filtered at the same time. With the aid of this filter, which has the characteristics of a low-pass filter, the harmonics are eliminated. so that the output voltage Ua corresponds to the fundamental curve in FIG. 3 corresponds. By means of a downstream RC element 26, a phase-shifted voltage Ub is obtained at the capacitor C of the /? C element. The course of Ua and Ub is shown in FIG. 6a shown

ss The voltage Ua is compared with the voltage Ub in a downstream comparator 27 (threshold switch). When the voltage Ub is less than the voltage Ua. so there is negative voltage at the output of the comparator: if the voltage Ub however, <* is greater than the voltage Ua. so there is a positive voltage at the output of the comparator. This results in the in FIG. 6b shown curve for the comparator output voltage Uk. The impulses of the compass rator 27 caused by the course of the voltage Uk can be scaled down in any ratio in the frequency divider 28 so that the positive or negative edges of the rectangular curve serve as a start / stop signal for the digital voltmeter.

η ^8th

can be turned. The Xe.Wer- Jung 4 ^ switched ^ w.rd ^ and ^^^, ^^ _άτ ^ determined

ratio is the time of the multiple duration, over wel mcrn ^ ^ ^ ^ ^. ^^ _t0 ^ ₀ . _Count got B

which the voltmeter averages. can be multiplied by that on the calibrated scale

In Fig. 7 the circuit of the £ _{wt shown in FIG. 4 can be} obtained. Digital voltmeters shown in a block diagram. 5 ^er ^^ _r ⁿ _{correction is done} by the fact that the Upper tIf a selectable time that _is to be measured _{by the} rake ASet _{to N Come}

In order to have a _{value shifted} to the input stan by a switch S 1 in counter B. As a divi-

an integrator t switched. The Integra or 1 «3f _e ^C _{rbaustein 13} a common digital IC is used,

an upstream resistor Rl aui at the input. _{The calculated} value is entered with cycle 1 via the AND

The integrator 1 consists of the verses Vl and _G , _{ied 12 taken over into the memory 7} and for display

the parallel arranged ^con d ^ ^at ° ^r _P ^ "J; ^ e ge 8 brought, for example by means of Nixie tubes.

Time T expires at time 1 (vgK Fig. 8) eme g 8 _{measuring arrangement according to F} j _f . 9 will also Reference voltage Uv averaged the switch 5 2 on the _difference , i _c her duration of the measuring time an exact

the input of the integrator 1 switched. During _{the kaUbrierten} p _hyslka l _1S chen unit overall

The back-integration time becomes the condensate Cl enta .5 ^ _{one of the} ^ ation-duration proportion «er

the. and the counter A adds up the: pulses: d «^ Fre ^ ^. ^^ _{Execution phone} n not digital

frequency generator 3. The count .st * "" PROPORTIONAL _m ^ ^ _{d MS ana, Sp ch} "s _{<t B} emes

tional of the voltage to be measured i / m. ^{The Α} "^ ^ηε _lnte grators are stored. At the beginning of the measurement is

of the integrator 1 is connected to the input of a Kompora J ^ ^ _{3 and} a switch S '5

tors 2 (threshold switch) connected, "ί _η . _ve rbün- opens, through which the capacitor C2 was discharged,

gear with a gate circuit 4 (AND-EtanentVvertan _gi ^ ^^ _{χ g} , _{calibration time} g _d , e to be measured

is the one that leads to counters A and B. De actu. * ^ _n , _{to the} input of integrator 1.

g ^ fc ^ terS'lundS '^ derT ^ J «« "^ ^ aL Switch 5'3 is the reference voltage

9 and 10 and of the counter is performed by e ne in Fi * 7 _In integrator 11, consisting of the Verstarke

Control logic shown only as a block 5 die ^ vo ^ outside, 5 υ ^ _{Capacitor cz} is switched on

the start impulse receives As indicated ^ and «jSjei _{output voltage} Ui of the integrator 11 proportional

cher and possibly a display device, _{d "r measuring time at} the end of the measurement phase opens

downstream _f . _ ... _{T = con} . Switch S '3 and switch S' 4 w, rd to the off

The measuring arrangement is reversed for a time base Γ = kon »reference voltage integrator 11

constant calibrated where Γ- ^ .I "VuJ" d ^M J ^ J ¹ JJ ₁ ³ ° Stet, so that the capacitor Cl of the integrator ^, 1

Generator 3 corresponds; with .st N a whole : JM _{Depending on} the integration voltage Lh

z. B in the one shown in FIG. 8 is W - *. ^ further understandable that at

¹ ta F? E ^ "st de ^g r voltage variation on YY ^" ^^ ^l £ ^ _n measuring time Γ also a high one! «* £» »

game represents the normal measuring point through ^. _{v £> rhanden} ^ _so that a faster

the time determined by the payer ß or an in 35 μ- _egratio n of the integrator C1 takes place

DeTsSeriogik 5 arranged counter requires a jerk m g ^ ^^ _{removed measurement}

IS 0W) 1pulse ^g e the frequency of the; Frequency gej «to« 3 splitters ^ ^ ^^^ ^ _v

counting all counters and memories are at the beginning ^^ g ^ ^ _{Konde "ΟΓ5 C2} to achieve

A a that the .integratjon be ₄ o ^ X ^ STS ^^^

H £ # | s £ SSSS

Counter 8 zagetührl «ird. . ¹ ^ f *? ^ S pre-counter, 6 success, through

sKCsasiMSg * - as, -tstszA o> -issxiZi

is enough, the compa '"^ _{i4 The measurement} can be started with Start ur

^ rT ₁ A ^ - »g ^^ Ä S.op.S _i8 na, e or d" rc * _ «*«. »., input voltage. so that this also ν «

certain limits can be chosen arbitrarily.

The same components are given the same reference symbols as in FIG. 7 provided.

As with F i g. 7, counter 6 or a counter arranged in control logic 5 counts the pulses and, when 10 ⁴ pulses are reached, gives a signal to terminate the measuring time. If a smaller or larger number of pulses is required to adapt the measurement time to the behavior of the measurement voltage, this or the stop signal ends the measurement time. The signals S1 and Sig b are given during the measurement time. By the signal 51, the measured voltage will To consisting t via the switch 5 '1 to the integrator 1 from the amplifier V and the capacitor Cl, with the interposition of the resistor R 1 connected Further, b by signal Sig voltage to the AND element 14 switched so that the frequency divider 15 - which converts the pulses of the frequency generator 3 with the frequency fo in pulses of the frequency fo / A , where A is a predetermined number, z. B. 100 is - transmitted pulses are allowed through and fed to the AND element 4 via the OR element 16. Since the control logic 5 and the comparator 2 also apply voltage to the AND element 4, the pulses are fed to the counter 6, which sums them up

When the measuring time ends, the signals 51 and Sigb are switched off in the control logic 5 and the signal Sig c is switched on first. By switching off the signal S1, the measuring voltage Um is switched off from the integrator 1, and by switching off the signal Sig b , the voltage from the AND element 14 is switched off so that further pulses from the frequency divider 15 are no longer allowed to pass to the counter 6. The AND element 17 becomes permeable through the signal Sigcv / ird , so that the count of the counter 6 is transferred to the memory 18. After the acquisition, the signal Sig c is turned off and the counter set 6 via the leading to the control logic lines to zero will now be 'closed by means of signal S 2 the switch S 2 and the reference voltage Uv connected to the integrator 1 while at the same time via signal Sig a voltage is switched to the AND element 20, so that the pulses transmitted by the frequency divider 19 are fed to the counter 6 via the AND element 20, the OR element 16 and the AND element 4. The frequency divider 19 is designed as an electronic counter, the final number of which can be marked by the memory 18. If z. B. the number 80 is marked so when this number is reached a pulse is sent and the counter is reset to zero so that a pulse is sent out for every 80th pulse of the frequency generator 3. At this point it should be mentioned that the frequency divider 15 can have a similar structure, but with the difference that the final number is fixed

As soon as the output value z. B. the value zero is reached, the comparator 2 tilts and switches off the voltage from the AND element 4, so that further pulses are no longer allowed to the counter 6. The signals 52 and Sig a are switched off and signal Sig ^ switched on. By switching on the signal Sig d , the count of the counter 6 is transferred to the memory 7 via the AND element 31 and displayed by the display device 8. The mode of operation of the in F i g. 11 is the arrangement shown in FIG. 12 explained. All counters and memories are cleared at the beginning of a measurement.

Assume that with a normal measurement time

ίο of 10,000 pulses through integration of the measuring voltage Um the integration voltage Ua is achieved. In the frequency divider 15, the frequency fo of the frequency generator 3 is scaled down in a ratio of 1: 100, so that of 10,000 pulses sent by the frequency generator 3 only 100 reach the counter 6 and are transferred from this to the memory 18 . After switching off the measuring voltage Um and switching on the reference voltage Uv , the system is integrated back. After 4500 pulses, the value "zero" or another output value is reached again and the comparator tips over. From the frequency divider 19, since the number 100 has been marked in this by the memory 18, only 45 pulses are sent to the counter 6. The number 45 is the measurement voltage Um directly pro-

Portionally and is transferred to the memory 7 and displayed by the display device 8. If the measurement is now carried out during a shorter measuring time of 8000 pulses, only the integration voltage Ua 'is achieved. The number 80 is added up in the counter 6 and is transferred to the memory 18 and marks the number 80 in the frequency divider 15, at which a pulse is sent out and the ring counter is to be reset to zero. During the reintegration, a pulse is now output for every 80th input pulse.

sent. Since the current integration voltage UA 'is less than the integration voltage Ua, fewer pulses namely 3600 to the frequency divider 19 are supplied during the return integration time, but since emitted at each input pulse 80, a pulse

is, a total of 45 pulses are fed to the counter 6. The same number of pulses is therefore used in the counter 6 counted as with a normal measuring time.

If the measuring time for another measurement is 18,000 impulses, i.e. it is considerably longer than the normal

times measuring time 180 pulses are summed up by the counter 6 and transferred to the memory 18. The frequency divider 19 then only sends out a pulse for every 180th input pulse. The integration voltage Ua "is reached after 18,000 pulses.

During the reintegration time, 8100 pulses are fed to the frequency divider 19 Every 180th pulse a pulse is passed on, are transmitted from the frequency divider 19 to the counter 6 8100: 180 = 45 pulses supplied, so that now too

again the same value is reached as with the normal measuring time.

It should also be mentioned that the invention is not restricted to the exemplary embodiments shown, for example instead of the one shown in FIG. 11 illustrated fre-

sequence divider 15 and 19 to form the quotient the measuring time and the reintegration time, another component can also be used.

See S sheet drawings

Claims (7)

Claims: 23 1. Device for weighing moving loads, whose force exerted on at least one load cell results in a time-varying electrical voltage curve, with a digital voltmeter based on the principle of double integration, in which first a voltage to be measured and then a reference voltage of opposite polarity on one Integrator with a downstream comparator (threshold value switch) are switched on and the integration time back to the initial value, measured by the number of pulses of a constant frequency, is a measure of the voltage to be measured, characterized in that the beginning and end of the measuring time are dependent on the movement sequence the load or the force path by switching center) (signal contacts M I, Λ / 2; Vorkontakie M 3, MA: comparator 27, frequency divider 28) loading to be tuned in that storage means (B-counter integrator 11, memory 18) of one of the store the value proportional to the variable measuring time and practice the re-integration time serving as the measured value r a switching device (multiplication element 13, integrator 11. frequency divider 19) can be corrected as a function of the stored value. 2. Apparatus according to claim 1, characterized in that the digital value proportional to the measuring time is stored in the form of a number of pulses in a memory (counter B) and the back integration time serving as the measured value (counter A) is digi'al in a multiplication component (13) the quotient of the normal number of pulses and the number of pulses stored (counter B) is multiplied for the measurement time. 3. Apparatus according to claim 1, characterized in that the value proportional to the measuring time is stored analogously as an integral value of the reference voltage in a memory (integrator 11, capacitor C2) and the back integration time serving as the measured value is analogously stored by the integral value of the dependent on the measuring time Reference voltage and the resulting steepness of the jerk integration is corrected. 4. Device according to one of claims 1 to 3 with a weighing bridge (22) over which the load (21) travels, characterized in that the beginning and end of the measuring time actuated by the load when driving onto the weighing bridge and when leaving the weighing bridge Switches (MX and M2) can be determined. 5. Device according to one of claims 1 to 3 for weighing oscillating loads, characterized in that that the beginning and end of the measuring time are determined by two oscillation maxima and minima will. b. Device according to Claim 1, characterized in that the value proportional to the measuring time is stored digitally in the form of a number of pulses in a memory (> o (counter B, memory 18) and the back integration time serving as the measured value is digitally stored with the interposition of a frequency divider, which is The ratio of the normal number of pulses to the number of pulses stored for the measuring time is preset, is corrected. 7. Apparatus according to claim 6, characterized in that one of the measuring time proportional Im- ₂