DE1303861B - - Google Patents

Description

Active and reactive components of the bridging 45 This deficiency is attempted by another well-known one Mood two identically structured, each other circuit (USA.-Patent 3 082 373) for the independent, one active and one bundle automatic balancing of a measuring bridge thereby ment in the comparison branch of the bridge assigned to avoid comparison impedances of different Units consisting of phased orders of magnitude are switched in such a way Rectifier, AND gates, second counter 50 that first a coarse adjustment and then progress and reversible counter are provided. an ever finer adjustment is carried out.

Such circuits are z. B. already well known from resistance decades ago. In this known bridge at the output a "mistake-ER ⁵⁵ folgs discriminator" used of the respective subsequent matching step with the previous

) The invention relates to an electrical compares and decides whether the following balancing for the automatic adjustment of an impedance step to improve the bridge equilibrium measuring bridge, in which the reference impedance has resulted in weight. If this is not the case, then will send bridge branch a number of switches 60 of each last switching step reversed the change of the through this bridge branch and the next finer series of comparison impedance 3 ends Stroms is arranged, advanced with one of the zen. Disadvantage of this known The fault circuit corresponding to the equalizing current is in particular the requirement of a geial emitting phased rectifier memory unit, which is the result of the previous one through this reversible and must store by means of 65 switching steps, and the difficulty : s clock incrementable reversible counter balancing of active and reactive components Control of the switching state of the switches, so-called impedances, because of the when balancing the with an individual component controlled by the reversible counter with regard to the other grain

3 4

component of the often strongly shifting adjustment point. binding with a capacity transformer-Me

As a result, the adjustment of the individual bridges, events

Notes must be repeated alternately. FIG. 2 shows a circuit diagram according to FIG. 1 under ν ei

The invention is based on the object of providing an illustration of further details, formwork of the type mentioned at the outset, FIG. 3 a transistor switch which, in a 1 and 2 can be used, impedances in a range of several decimal Fig. 4 and 5 possible arrangements aer ^ n dical orders of magnitude with little circuitry for the reference impedance and oleichzeitiee technical effort and which in particular enables Fig. 6 a block diagram for me gieu. & which has these advantages even when effective measurement of capacitance and conductance. Trans and reactive components are to be matched. In FIGS. 1 and 2, the W »i

This object is achieved according to the invention, starting from the formator measuring bridge, uie rrim

through between the clock and the individual ment P of the transformer T is from a

Decade inputs of the reversible counter generator 6 _{fed with alternating current i} , so that one. P.

switched, from a second counter controllable voltage in the secondary winding S with a ge

AND gates and a phase-controlled center tap G is induced JJieo ^ u

Rectifiers connected downstream, in each case with phase the secondary winding 5 form bridges

reversal of the compensation current, a count signal to the other two branches chunks hegenJ> ^ne

second counter emitting voltage comparator, known capacitance C _x and a known ν erg

where the outputs of the second counter the AND 20 capacitance C ₅ (reference capacitance).

Links are assigned in such a way that from the second the bridge is balanced when deMrom

When it is incremented, the counter is that of the bridge branches with ^the comparison capacity C

next lower decade of the reversible counter and the unknown capacity C _x g'jcn si

assigned AND element is controlled. By means of that no compensating current in Jf ^r Aus ^ e e ^ ru g

this circuit is a around the balance point, 5 by a phase controlled ^{equi ch} "™ \\ _{h & T}

convergent oscillating adjustment achieved. The connection lies between the bridge corner point load

control of the individual meter decades using de! the ground connection G on the B ^M ™ ^ n Brocxen

AND elements and the second counter is corner point G. The phase-controlled equi> cn sr J

very easy. determines whether the bridge ^ ^two | ^^

Conveniently, 30 current flowing in the voltage comparisons big or small "as; aei uu rather a the bridge arm C flowing overall from the phase-controlled rectifier, he delivered DC voltage with a fixed Bezugsspan- while an error signal indicating ^ if ^z ™ ^b ™ ^c ^ voltage compared and the comparison signal is fed to the second counter _{via an adjustment in the bridge branch C 5, an old OR element.} Required to lower voltage .n '£>"[· _A Thus, the second counter is so long ^and with 35 magnitude of the voltage ^{mi' e} ^, ^ ^r f? Supplied a reStrom nd when the phased rectifier taps on the secondary winding, and ™ ter supplies an error signal. As soon as the adjustment of the contact Γ changeable woto dieA ^ swah is enough, however, the second meter of the tapping points is de-energized via electronic switches and thus the reversible meter is shut down. he follows. The error signal is given by fme *

The logic circuitry described in more detail can be used in a particularly advantageous manner

circuit according to the invention in the known trans works and a reversible Zamer £ 8

formator bridge circuits with a number that leads via lines JO by means of the eieKtro ^

Switchable taps on the secondary winding use the circuitry the voltage at c, s.

the. A measuring device constructed in this way can ^{detect an error signal e} F ⁿ '. ^zaht _r £ _ne m state of

Allows capacitance measurements from 0.0IpF to 45 balance achieved. At f ^^^ SP ^

100 μΡ and an adjustment within less than a bridge becomes the value ^ ^r . ^u ° ^ «placed on the

one? have a second "one Exactly from one " £ -% $ £££ & S, ■ * -

"If active and blind com information are also to be ^{compared to the Ve} ™ enau & ponente at the same time, two identical 50 printing devices or otherwise built, independent, one effect and processing systems at 22 im b.narverscniub a blind element in the comparison branch of the bridge painting _system .

assigned units, consisting of phase- In the execution ^η ™ ^η Β ^^ " ^Η ^ 4 ⁸ _d te Araap-

controlled rectifier, AND gates, second len the electronic Digitelbchalter 4 ate απ ρ Suilcr and reversible counter, provided. The ₅₅ function Γ on the secondary winding S, whereby the pha-convergent oscillating simultaneous adjustment of the bit-controlled Gtadinchter 3 em tension of the components prevents the occurrence of which corresponds to the analog value ^U J ^U1 f "· _d · _{A of the} adjustment points, so that an alternating counter 19 does not need to be used to adjust the two components. The tap selected which enables a circuit according to the invention therefore leads to a 60 equal. Switch 4 is in

high synchronization speed. Manufacturing technology A preferred arrangement of ^the J ^

The advantage here is that the two compo- F i g. 2 shown. H.erbe. are in succession, The circuits used have the same structure unt ^ rsc ^^^, fg ^ pSffi ^ SSSr

"" Embodiments according to the invention are 65 T ₁ , T ₂ ... T ₃ to the same nominal capacitance enC J ^

which are explained in more detail below on the basis of the drawings. The switches are shown schematically

purifies. It is preferably transistor switches, as shown in Hg. J

Fie. 1 shows a block diagram of the circuit in FIG.

If the bridge is unbalanced, a DC voltage is produced at the output of the phase-controlled rectifier and is fed to a voltage comparator 9 via line 5. The voltage comparator 9 belongs to the logic circuit 20, the remaining circuit elements of which are described in more detail below. The direct voltage is compared in the voltage comparator with a reference voltage supplied at 7, which, for example, has ground potential. If the bridge is unbalanced, the output signal of the phase-controlled rectifier is higher or lower than the reference voltage, so that a signal is obtained at the output of an OR gate 11 which controls a counter 13 via a line 15. The counter 13 has in FIG. 2 four outputs D ₁ , Z). ,, D ₃ and U ₄ , which are connected to corresponding AND gates G ₁ , G ₂ , G., and G ₄ , the synchronous clock pulses from one (via 8 with the Current source related) clock 17 received to feed corresponding decade inputs 8 'of the reversible counter. In order to indicate the direction in which the reversible counter 19 is to count, a direction-indicating direct control voltage is applied to the reversible counter 19 via 2. If the detuning control signal has a value that the counter country is higher than that required for an adjustment, the counter 19 is caused to count down and vice versa.

If the bridge is unbalanced, the counter 13 initially emits _{a signal at the output Z) 1} , so that the gate circuit G ₁ allows pulses from the clock 17 and feeds them to the highest decade of the reversible counter 19. The highest decade continues to count until it has counted beyond the adjustment point, whereby the polarity of the error signal is reversed. This reversal causes a change in the state of the output of the voltage comparator 9, which is passed via the OR gate 11 and the line 15 to the counter 13 and results in the counter emitting a signal at the output D. the gate circuit G ₂ opens. This means that 8 'clock pulses can be fed to the next decade input. Further changes in the state of the comparator 9 cause a corresponding control of the counter 13, so that it is _{advanced to the outputs D. or D 4} and the gate circuit G ₃ or G _{4 is} opened. The counter 19 has the normal carry paths from each decade to the next higher decade.

The output 10 of the reversible counter 19, which indicates the counting direction and thus the direction of the required correction of the tap on the secondary winding 5 of the transformer T, can control the switch 4 shown schematically in FIG. The tap T is automatically and continuously searched for with the successive switches T ₁ , T ₂ , T ₃ etc. in order to change the voltage conditions in the bridge branches. The count in the reversible counter 19 is directly proportional to the current that flows through the normal capacitance C ₅ through the switches that are appropriately actuated and assigned to the correct transformer tap 7 ″ _x. the switch 4 so take the digital signal and generate a current in the normal capacity C "corresponding to the analog value of the count in the reversible counter.

The switches T ₁ , T ₀ , T ₃ etc. can, for example, be two-stage transistor switches with parallel-connected base outputs and a common emitter (FIG. 3). Using the variable voltage from the various taps in Figures 1 and 2 is only one possible way. Another way is in FIG. 4, where instead of several comparative capacitances of equal size according to FIG. 2, which are each fed with a different voltage, several capacitances C _n ... C _{v ;!} etc. are with graduated values and a common connection of the switches T ₁ ... T _s etc. to the upper connection of the secondary winding 5 exists. This circuit enables different (for example, each doubling) capacitance values to be switched on in the upper branch of the bridge.

Furthermore, as shown in FIG. 5, a single comparison capacitance C ₅ can be used, the current flowing through it corresponding to the state of the switches T ₁ , T _v T _a etc. and the resistors R ₁ , R ₂ , /?., Etc. assigned to them, the can be switched depending on the count of the reversible counter 19. The voltage at B is created by applying the cumulative outputs of the switching devices to a common amplifier A, which is used to produce high linearity and stability

, _{0 works} with considerable negative feedback at R. By means of this digital-to-analog conversion, the ratio of the alternating voltage at B to the alternating voltage at the input is changed, so that the impedance value of the normal capacitor C ₅ in the bridge circuit is effectively changed to effect the adjustment.

For the sake of illustration, the bridge circuit according to FIG. 1 and 2 have been described on the basis of automatic capacitance measurements, although inductance and conductance measurements can also be made if desired. In the circuit according to FIG. 6 is the capacitance measurement according to FIG. 1 and 2, for example, by a Leitwerimessung crgäiul. The unknown conductance G _x is determined in parallel with the unknown capacitance C ₁ . Here a digital-to-analog converter 4 'with an additional phase-controlled rectifier 3' is used, which applies an output shifted by 90 'to a separate set of logic circuits 20' and a reversible counter 19 ', the individual connections with the F i G. 1 corresponding reference numerals are designated.

In practice, bridge circuits of the type described above can be carried out successfully in such a way that automatic balancing can be achieved in the manner described above. For example, with a 400 Hz power source 6, a capacitance range (parallel connection) from 0.01 pF to 100 μΡ, a conductance range (parallel) from 100 pS to 1.0 S and a directly readable loss factor range from 0.0001 to 1, 00 (100%), all with a reading accuracy of 0.1% for capacitance and conductance and of 1%> for the reading accuracy of the dissipation factor. An automatic adjustment χ in 0.35 seconds can be achieved without changes in the range.

1 sheet of drawings

Claims (4)

1 2 j _, ... display and / or output device for the claims to be: measuring component of the impedance. j 1. Electrical circuit for the automatic There are various types of impedance] Adjustment of an impedance measuring bridge in which the measuring bridges are known. To create an automatic ab- j To enable the same bridge branch 5 having reference impedance, the impedance, current j a number of switches for the change or voltage ratios in the comparison branch of the of the bridge current flowing through this bridge branch can usually be digitally switched. In particular, it is arranged that a number of comparison impedances can be rejected or connected together with an error signal corresponding to the phase of the off, in order to reduce the current flowing through the comparison branch and the current flowing through the comparison branch this reversible and by means of change. Alternatively or additionally, may continue switchable of a clock at \ reversing the board particularly suited f for the automatic adjustment counter for controlling the switching state of the Neten transformer measuring bridge different down switch and with a by reversing the secondary winding handles of the transformer j counter controlled display and / or output 15 be switchable to the device at the reference impedance an- j for the component to be measured of the voltage present and thereby the through this | Impedance, characterized by changing the current flowing between the bridge arm. 'See the clock (17) and the individual De- A circuit for the automatic adjustment of a cadence inputs (8') of the reversible counter measuring bridge of the type mentioned is z. B. from (19) switched from a second counter (13) 20 of British Patent 744 364 known. In the case of the controllable AND elements (G ₁ ... G ₄ ) and a known circuit, the unknown impedance can be adjusted to the phase-controlled rectifier (3). B. consist of a temperature sensor, softer: switched, each time a phase reversal of the output changes its value within relatively low ■ direct current a counting signal at the second counting limits. Because impedance changes in both LER (13) emitting voltage comparator (9), 25 directions are possible, the counter must be controlled in sense I wherein the outputs of the second counter (13) to be the bar. For this purpose, an alternating voltage is fed in at two bridge AND elements (G ₁ ... G ₄ ) assigned to corner points and; are that the second counter (13) at whose which can flow \ between the other two vertices of each switching operation the the next lower sequent circulating current through a transformer with \ decade of the reversible counter (19) züge- 30 secondary-side center tap to Phasensteuc-; ordered AND gate is controlled. tion fed two diodes, each with one 2. Circuit according to claim 1, characterized by winding a changeover relay with neutral idle * indicates that in the voltage comparator (9) position are connected. By means of the relay, the controlled by a phase-controlled rectifier (3) reversible counter. The counter changed supplied DC voltage with a fixed reference voltage by opening and closing switches is compared and the comparative equal impedance is within specified limits, signal via an OR gate (11) to the second The gradual change in the comparison impedance Counter (13) is supplied. takes place continuously during the adjustment. Such a one 3. Circuit according to claim 1 or 2, but marked circuit is poorly suited for the measurement: is characterized by its use for a transmission of impedances in a range of several i formator bridge circuit with a number of decadic orders of magnitude, as on the one hand switchable taps on the secondary winding (5). too many comparison impedances; 4. Circuit according to claim 1, 2 or 3, there would have to be provided and also the adjustment characterized in that it would take far too long a time for the adjustment.