DE1548694C - Test device for the digital display of the measurement error of a measuring device which measures the time integral of a variable - Google Patents

Description

The invention relates to a test device for the digital display of the measurement error of a measuring device, which measures the time integral of a quantity. To the group of measuring devices that use the time integral

German

determine any variable α include, for example, electricity meters, ampere-hour meters and flow meters for gases and liquids.

These measuring devices generally suffer from a measurement error. The determination of the same is usually done in such a way that the measurement result displayed at a certain point in time of the measuring device to be tested is compared with the measurement result obtained at the same point in time of a reference measuring device regarded as error-free, which, starting at the same point in time as the test object, is the time integral the same size α measures. The relative measurement error F "=:

of the test item, where l / l = A'-A is the deviation of the measurement result A 'of the test item from the reference integral / 1, ie from the integral value measured by the reference measuring device. If no special auxiliary measures are taken, the determination of the relative error after the measurement has been carried out still requires a division, which requires trained personnel. B. occur in electricity meters, is very annoying because of the time involved.

The invention is based on the object of creating a test device which determines the relative deviation the measurement result of the device to be tested directly from the measurement result of the reference measuring device digitally, regardless of the duration of the measurement time and regardless of whether the variable to be integrated over time is constant or not during the measurement time. The digital display should be done in the usual way by means of a pulse counter that counts the pulses from a Pulse generator can be delivered.

This object has now been achieved according to the invention in a test device for digitally displaying the measurement error of the time integral! a measuring device measuring a quantity compared to the measurement result of a second reference measuring device measuring the time integral of the same quantity with the same start of integration using a pulse generator and a pulse counter serving as a display device in that the pulse counter serving as a display device for the relative deviation is connected to the output of a pulse generator, of from the time in which first reaches a preselected value the measurement result of only one of the two measuring devices, to the time, in which the measurement result of the other ^{f) 0} meter same value has been reached, each then provides a pulse when has increased starting from the first-mentioned time, the reference integral as shown by the measurement result of Referenzmeßgerätes by an amount proportional to the ^f> 5 since the integration start accumulated until that value of the reference integral.

Details of the invention are described below with reference to the drawings Working examples. It shows

F i g. I a diagram,

F i g. 2 a block diagram,

F i g. 3 shows a circuit detail and

F i g. 4 another block diagram.

To explain the invention, it is initially assumed that the display comparison of two electricity meters is involved, both of which integrate the same power P , which is not necessarily constant over time, with the same or different constants. Both measure the electrical work from the start of measurement at time / = 0

AU) = f 1 '(I) UI.
0

The display of one counter, the reference counter, is assumed to be correct; it represents the reference integral A (l ·) . The other counter is the test item. A pulse generator, the pulses of which are fed to a pulse counter, begins to work at the moment at which a preselected measured value A ₁ from one of the two counters. is achieved. At this moment the reference integral, which is identical to the display of the reference counter, has the value Λ ,. If the reference counter is the first to reach the preselected measured value A _1. , Then / I ₁ = / 1,., In the other case / I ₁ <, -I ,,. The pulse generator now generates pulses, the frequency of which is not constant, but is related to the increase in the reference integral. When the reference integral increases by the differential d / 1, the number η of the total output pulses increases by, the differential quotient j being the one since the start of the measurement

accumulated value / 1 (0 of the reference integral is inversely proportional. The following applies:

ddl

where m is a constant which determines the resolution of the error display.

The output from the pulse generator pulses advertising "the now counted so long, has to also the second counter reaches the preselected measurement / I _1,. Meanwhile, the reference integral to the value A ₁ is increased, and the number of pulses of the pulse generator during of the increase in the reference integral from the value .1 to the value / 1

,1,

Y A (I) A ₁

A ₁

With I / 1 = A ₁ - / I ₁ one can write for this:

I ₁ )
Series expansion gives

I / 1 I / I A \ ^z 1 / I AV

// = in ■ In, = in · In [I

- in

Γ I / 1 I / I / IY 1 / I AV Ί

If the higher order terms are neglected, this gives the approximation

( ^iA

The number η of the pulses counted by the pulse counter can with sufficiently small values of _T -

■ M

with a satisfactory accuracy than the measurement error 1.1

of the test item. With

/ H = 1000 gives η the measurement error in per mille. The one calculated with the exact value of η

reli er heat between the value of the error Fi = 7

and the mistake Fi = one gets,

if the deviation I A is related to A ₁ instead of / I ₁ .

You can write:

'Ld

/ I ₁

and, if you develop the last fraction into a series,

(i-Ητ) -

If, which should only rarely occur, the quantity, the time integral of which is to be determined, does not itself depend on time, but is a constant, then its time integral increases proportionally with time, i.e. it is A ~ f. In this case the following would apply to the number η of the pulses emitted by the pulse generator:

45

■ iy

/ I i

-.- - m ■ In - = »ι -In - ^ ---, related to the reference integral, Ί (ί) after a monotonically increasing but otherwise arbitrary function ^ i = ^ i ['U')]. A second, similar quantity is linked to the reference integral through a function

U ₂ = U, [/ l (0] =. U ₁ Im [ZUf) -Zl (OJi

connected, which differs from the function υ, [. 1 (ί)] only by the constant multiplication factor m as well as

ίο differs in that it begins to grow again at successive points in time f "with η = 0, 1, 2 ... _{starting with the value U 1 (O).} For the first time, the function U ₂ begins to appear at the point in time f "at which one of the two measuring devices, ie z. B. one of the two electricity meters, the predetermined measured value .I ₁ . has reached. The following point in time f, and all further points in time f, "at which the function U ₂ begins to increase again with the value U ₁ (0),

zo are each determined by U ₂ = U ₁ . This is achieved by the fact that each time U ₂ and U _{1 have} the same values, the variable U _{2 is} suddenly reduced to the initial value U ₁ (O). From Fig. 1, where an example of the profile of the variables U ₁ and U ₂ as a function of the reference integral.-I is shown, it will be seen as follows: At the time ₍₎ f, in the first one of the two counters of the preselected measurement value / I ₁ , is reached, A = Ai ₁₁ , U ₁ = U ₁ (O) '. At this point in time f "

U ₂ begins to grow from the value U ₁ (0). At the point in time f ₁ , where the reference integral A has reached the value At 1, is.

U ₂ = U ₁ , ie U ₁ Im (At ₁ -A _1n )] = U _x (At) -

This is repeated in the following time segments f ₂ , / ₃ etc.

In general \

50

if f, and f _{2 are} the times at which the first and the second measuring device the. predetermined measured value A ₁ . So you only need here for that

to ensure that V-, but that is the frequency / with which the pulse generator emits pulses after the Relationship / = - the integration time, conversely pronortion-il it

With reference to Fig. 1 will now be explained how the pulse generation according to the relationship

to in:

- -

UA A (I)

can take place. A physical quantity, preferably a tension, is created that

U ₁ [»1 {A _tj - A,. J] = U ₁ (^ l) with / = 1,2,3 ..., and it follows from this, if one sets ^ - ^^ = Λ / 1,

AA ₁ = -A ₁ . in

Now every time U ₂ = U ₁ , a pulse is sent to the pulse counter. If one designates with / the sequence density of these impulses, by which the number of impulses is to be understood, which is to be understood during the increase of A by one unit, so is

AA A

If d / 1 denotes an increase in / !, the

is very small compared to AA , which in turn is so small that the momentum density can be regarded as practically constant over the range l / l. this area

d / i = / d, -l = in -d.-l A

Impulses. The total number of pulses resulting from an arbitrarily large increase / I ₂ - / I _{1 of} the reference integral

omitted, is then, exactly as already derived, again .

d A ^ m -

So the impulses will turn from the point in time when the first to the point in time when the second counter reaches the preselected measured value, counted, the result / i of this count is the same the measurement error of the test object, namely if «ι = 1000 is chosen, directly in per mille.

As already mentioned, the function Vi [A) can be any function that increases monotonically with A. Up until now it was tacitly assumed that U ₁ and U _{2 were} continuous functions of the reference integral A - albeit only piecewise. But this is by no means necessary; The smooth courses of these functions can also be approximated by means of stair curves, consisting of vertical and horizontal pieces. If the graduation is sufficiently fine, the accuracy of the error measurement is not noticeably impaired. This gives the possibility of z. B. to maintain the usual pulse scanning of the change in position of the measuring devices when testing electricity meters. In the case of counters, this can be, for. B. done by foloelectric scanning of marks applied to the counter disc edge, the scanning device then delivering pulses, each of which corresponds to the rotation of the counter disc by a specific angle of rotation and thus the increase in the measurement result by a specific amount of electrical work.

In this case, the sampling pulses of at least the reference counter are expediently multiplied in a pulse multiplier in order to subdivide the increase in the reference integral into significantly smaller jumps than is possible with the mark division on the counter disc alone. If each output pulse of the pulse multiplier then increases the independent variable A of the functions U ₁ and U ₂ by a certain amount, the gradation of the course of these functions can be made as fine as desired. The reference counter can deliver a pulse frequency of at most 500 Hz; what is desired, however, is a highest step frequency of a few kilohertz, e.g. From 7.5 kHz.

The following principle can be used for pulse multiplication applied: The pulses to be multiplied are fed to a monostable multivibrator, which delivers a precisely defined voltage-time integral for each input pulse. The consequence of so shaped pulses are averaged so that a voltage proportional to the input frequency is obtained. This voltage then controls an astable multivibrator with linear voltage-frequency characteristics, which means the desired, higher pulse frequency supplies. ·

The variables U ₁ and U ₂ - which are dependent on the reference integral A , are, as already mentioned, expediently formed by voltages. These voltages can be generated in that each output pulse of the pulse multiplier supplies two capacitors with the capacitances C _x and C ₂ a defined amount of charge Q. Then the voltages IZ ₁ and U ₂ on these capacitors increase with the number of pulses z. B. after a c-function. If the capacitance is made C ₂ = ■ C ₁ , then it increases

the voltage U ₂ m times as fast as the voltage U ₁ .

The charging of the capacitance C begins already at the beginning time ί = 0 of the measurement, the charging of C ₂ only at the moment when the preselected measured value A ₁ . is reached (time / "). In the further course, the capacitance C ₂ . Every time the voltage U ₂ on it has become equal to the voltage V ₁ , it is suddenly discharged again. With each discharge, a pulse is fed to the pulse counter. The further generation of these pulses or at least their further counting by the pulse counter is interrupted as soon as it does the other electricity meter has reached the selected reading A _x .

F i g. 2 shows a block diagram of a pulse generator constructed according to the principle mentioned. At input E , the possibly multiplied pulses of a defined duration, each representing a certain increase in the reference integral appear and charge the capacitors C ₁ and C ₂ via the resistors K ₁ and R ₂ and the diodes D ₁ and D ₂ , which cause a re-discharge impede. If '/ ?, = R ₂ , then C ₁ = m C ₂ . The two capacitors C | and C ₂ resulting voltages U, and U ₂ are compared with one another in a zero voltage amplifier 1. When U ₁ = U _2, this controls a discharge circuit 3 via line 2 so that C _{2 is} discharged via 3 and lines 4 and 5. The zero voltage amplifier must meet the following requirements:

1. For U, = U ₂ , its inputs must be very high resistance so that its input currents do not influence the course of Ui (A) and U ₂ (A) .

2. When C ₂ is discharged, no additional charge may flow to or from _{the capacitor C 1 , since otherwise U 1} would be falsified.

3. When Ui = U ₂ , the amplifier must be able to deliver a pulse that can be used to release the discharge circuit 3.

When the control pulse arrives via line 2, the discharge circuit 3 must change very quickly from a very high-resistance state to a "very low-resistance state. If, after C ₂ has been discharged, no more current flows through the discharge current path, the discharge circuit must immediately become high-resistance again. As Discharge circuit, for example, a monostable multivibrator with a very low-resistance output or a controlled four-layer diode can be considered.

A circuit example of the "serving for the delivery of counts pulse generator is shown in Fig. 3. From the reference device or the nachgeschalleten pulses multiplier pass positive pulses of defined duration to the input E. When the switch S _{1 is} opened and is located at the control inputs

If the output S _{2 has} a positive voltage, the capacitors C ₁ and C _{2 are} charged step-by-step with each pulse encountered at £ in accordance with their capacities and the resistances R ₁ and R _2, respectively. The rise in voltage U ₁ across capacitor C ₁ is

coupled out through the transistor Q _{3 with a} very high resistance. -

The transistors Q ₁ and Q ₂ work here both as zero voltage amplifiers and as controllable ones

Discharge circuit. As long as the voltage LZ ₂ at C _{2 is} less than the voltage LZ ₁ and C ₁ , the transistor Q _{1 is} blocked. When U ₁ = LZ ₂ , the transistor Q ₁ begins to conduct; a small current flows from its emitter to the collector and from there to the base of transistor Q ₂ . Q ₂ draws the increased current through R ₃ , which in turn makes Q ₁ more conductive and thus initiates a regenerative process which results in a complete discharge of C ₂ . If after discharge of C ₂ no more discharge current flows through the emitter of Q ₁ , this transistor begins to block again.

Part of the discharge current from C ₂ is via R ₄ . fed to the base of transistor Q ₄ , whereby an amplified discharge signal in the form of a voltage arises at its collector resistor R ₅ , which causes a monostable multivibrator consisting essentially of the transistors Q ₅ and Q ₆ and the coupling capacitance C _{4 to tilt.} Its output signal is fed to an output amplifier with transistor Q _{1 via capacitor C 5} , so that a defined output pulse of a certain duration is generated at its output A each time capacitor C ₂ is discharged, i.e. each time LZ _{2 is reset, which is fed to the counter} will.

The potentiometer P ₂ serves as a voltage generator for the closure of the switch S ₁ , via which the capacitor C ₁ is then discharged in order to prepare the pulse generator door for a new measurement.

By applying a negative voltage to the control input S ₂ , the generation of pulses can be prevented by the charging current for C _{2 being} diverted via the diode D _5.

In Fig. 4 finally shows a block diagram of the entire device. At the input of a coming representing the increasing measured value of the test piece, at the entrance to the reference integral representing pulses to b. The first pulse of the test object tilts the bistable multivibrator F ₁ into the measuring position, and thereby gate G is opened via the line 7 at the same time. The pulses of the reference _{integral are now counted into the counting chain Z 1} , while the pulses from the test object are counted into the counting chain Z _2. The overturning of F _{1 also causes the switch S 1 to} open via the control line 8 (see FIG. 3), so that the capacitor C ₁ in the pulse generator or oscillator O is connected to the input via the pulse multiplier M. E supplied pulse of the reference integral begins to charge. At the control input S _{2 of} the oscillator O is initially still a negative voltage.

The two counting chains Z ₁ and Z ₂ are equipped with a preselection device in such a way that each of them emits a pulse when a preselected number is reached, corresponding to a preselected integral value A _1. The same integral value A _x is used on both counting chains . corresponding number preselected. If one of the two counting chains now reaches the preselected number, the resulting output pulse is _{fed to a bistable multivibrator F 2} and causes it to tilt. The unstable multivibrator F ₂ applies the control input S _{2 of} the oscillator O to positive potential via the line 9, so that the oscillator now generates pulses which _{are counted in the counting chain Z 3} , on which the test object's measurement error is to be displayed.

After a while, the other counting chain will also have reached the preset number. The control input of the bistable multivibrator F ₂ then receives a second pulse from it, by means of which it is tilted back into its initial state. In doing so, it puts the control input S _{2 of} the oscillator O back to negative potential via the line 9, which prevents it from further emitting pulses. The number of pulses which oscillator 0 has emitted in the meantime and which _{have been counted in counting chain Z 3} corresponds to the relative deviation of the test result from the reference integral. This measurement error can be read off immediately in digital form _{at Z 3.}

The sequence of the output pulses of the counting chains Z ₁ and Z ₂ can be used directly to determine the sign of the error: If one state of a bistable multivibrator means +, the other -, then, depending on the definition of the sign, the output pulse of Z ₁ this bistable multivibrator to -, the output pulse from Z ₂ to + or vice versa.

Claims (7)

Patent claims: 1. Test device for digitally displaying the measurement error of a measuring device measuring the time integral of a variable compared to the measurement result of a second reference measuring device measuring the time integral of the same size with the same start of integration using "a pulse generator and a pulse counter serving as a display device, characterized in that the display device for The pulse counter (Z ₃ ) serving the relative deviation is connected to the output of a pulse generator (O) _{which starts from the point in time (i 0} ) at which the measurement result of only one of the two measuring devices has initially reached a preselected value [A ₁ ) , up to the point in time at which the measurement result of the other measuring device has also reached the same value [A ₁ ) , then delivers a pulse if, starting from the first-mentioned point in time (i ₀ ), the reference integral represented by the measurement result of the reference measuring device (Λ ) has increased by an amount (δ A) equal to that since the integration sbeginn (f = O) up to then accumulated value of the reference integral [A) is proportional. 2. Device according to claim 1, characterized in that the criterion for triggering the individual output pulses of the pulse generator (O) is the equality of values of two similar quantities (IZ ₁ , U ₂ ), preferably two voltages, of which the first (IZ ₁ ) at the beginning (/ = O) of the integration time (f) with a certain value U ₁ (0), preferably with the value zero, starting after a certain, in particular an exponential function U _x A [t) with the reference integral A (t) increases monotonically, while the second variable (LZ ₂ ) is derived from the value LZ ₁ (O) for the first time at the point in time (f ₀ ) at which the measurement result of one of the two measuring devices has reached the preselected value [A,] or zero out according to a function U ₁ A (I), which with the function U _{ A (t) 109 «24/154 except for a constant multiplication factor (in) of the argument, increases with the further increase of the reference integral (A) and this subsequently every time it has reached the value of the first variable U ₁ after resetting to the value IA (O ) or zero is repeated until the measurement result of the other measuring device has also reached the preselected value (A _v ) . 3. A device according to .Anspruch 2, characterized in that the two variables (U ₁ , U ₂ ) whose coincidence serves as a criterion for triggering an output pulse of the pulse generator (O), through the voltages of two capacitors (C ₁ , C ₂ ) are formed, whose charge is increased in accordance with the increase in the reference integral and of which one capacitor (C ₂ ), whose voltage (CZ ₂ ) rises more rapidly with the reference integral, each time when the voltage is equal to the other capacitor (C ₁ ) by closing one Discharge circuit (3) is discharged again. 4. Device according to claim 3, characterized in that when the measurement result of the reference measuring device is converted into pulses, each of which corresponds to an increase in the measurement result by a certain amount, each of the two capacitors (C ₁ , C ₂ ) has a predetermined charge for each pulse is supplied-. 5. Device according to claim 4, characterized in that the two capacitors (C ₁ , C ₂ ) have different capacitance values, while the associated resistors (R ₁ , R ₂ ) have the same value. 6. Device according to claim 4 or 5, characterized in that the pulses generated directly by scanning the reference measuring device, the increase in the reference integral (A) by a certain amount corresponding to their further processing to charge the capacitors (C ₁ , C ₂ ) are multiplied . 7. Device according to claim 3 or one of the following claims, characterized in that the more slowly increasing capacitor voltage, coupled out with high resistance _{by means of a first transistor (Q 3} ), is fed to the base of a second transistor (Q _{1 ) via a resistor (R 3)} whose emitter is connected to one pole of the other capacitor (C ₂ ) and whose collector is connected to the base of a complementary third transistor (Q ₂ ), the emitter of which is connected to the other pole of this capacitor (C ₂ ) and its collector is connected to the base of the second transistor (Q ₁ ), so that if the second transistor (Q ₁ ) begins to conduct when the voltages on the two capacitors (C ₁ , C ₂ ) are equal, the collector current caused by its collector current of the third transistor (Q ₂ ) at the resistor (R ₃ ) causes a voltage drop, which _{drives the second transistor (Q 1} ) further into the state of conductivity and de r capacitor (C ₂ ) discharges through these two transistors. 1 sheet of drawings