DE1205186B - Resistance bridge circuit for a self-balancing compensator - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

Number:
File number:
Registration date:
Display day:

GOIr

German class: 2Ie-32

1205 186
S86894IXd / 21e
August 26, 1963
November 18, 1965

It is known, the compensation voltage, which in a self-balancing compensator a Measurement voltage is switched in the opposite direction, to be taken from a resistance bridge circuit. With a well-known Device of this type, the bridge circuit contains a linear potentiometer, whose tap is moved by a balancing motor until the tapped bridge voltage of the measuring voltage is equal to. The adjustment motor is based on the difference between the measurement voltage and the compensation voltage driven. The differential voltage is usually calculated with the help of a so-called Amplified zero amplifier. The known arrangement has various shortcomings that have been in use until now self-balancing compensators have severely hindered some tasks or measuring ranges.

It comes z. B. in a known device of the type described above that the grinder of the potentiometer so heavily soiled by dust or oxidation products that the electrical contact is interrupted. Due to the nature of the circuit, the zero amplifier then receives no input voltage and the adjustment motor is not moved. This corresponds to the same operating status as it exists after a calibration has been carried out. The mistake is therefore not displayed by the compensator. In this way, incorrect measurements are possible.

Another disadvantage of the known bridge circuit is that contact and thermal voltages, that occur on the movable wiper of the potentiometer are in the compensation circle and lead to considerable errors, especially when measuring in the lower voltage range.

The invention relates to a resistor bridge circuit which eliminates the above-mentioned deficiencies cling. The circuit is used to generate the compensation voltage for a self-balancing Compensator with at least one potentiometer, the latter of which can be displaced by a balancing motor Tap represents a branch point of the resistor bridge.

According to the invention, the bridge arrangement is characterized in that two fixed diagonal Branch points of the bridge circuit supply the compensation voltages and in the other the Slidable tap containing bridge diagonal a preferably shaped stream is fed.

A supply of the resistor bridge with an impressed current can be dispensed with, when the compensator is used with passive transducers in series with the Compensator fed from a common source

Resistance bridge circuit for one
self-balancing compensator

Applicant:

Siemens & Halske Aktiengesellschaft,

Berlin and Munich,

Munich 2, Wittelsbacherplatz 2

Named as inventor:

Dipl.-Ing. Dr. Klaus Horn, Karlsruhe

will. It is ensured that the ratio of the supply voltages of the transducer and the Compensator remains the same.

If the sliding contact of the potentiometer is interrupted in the bridge arrangement according to the invention, so a substantial part of the measuring voltage is at the input of the zero amplifier without its counteracting compensation voltage. The adjustment motor is therefore moved to an end position; thus the interruption of contact on the potentiometer is indicated by the compensator itself. Incorrect measurements due to an interruption in contact with the potentiometer are therefore excluded. the Supply current source for the impressed current also causes a at the point of interruption voltage so high that oxidation or dust breaks in most of them Cases are burned out and thus cured.

The contact and thermal voltages still occurring on the potentiometer wiper are at Bridge arrangement according to the invention no longer in the compensation circuit and therefore affect the Measurement no longer.

Another advantage of the invention over the known arrangement is the fact that the The output resistance of the bridge arrangement does not depend on the tap position, but is constant is. This has an advantageous effect on the setting time of the self-balancing compensator. aside from that the output of the bridge arrangement can be loaded without a linearity error occurring. This Factor can be used for a simple switching of the measuring range by switching on the appropriate load resistors be exploited. This type of measuring range switching is beneficial in that the internal resistance of the bridge arrangement with small

509 738-56

As the measuring range becomes smaller, the compensator is always a favorable adaptation having on the test object.

It is known that in a Wheatstone bridge the food diagonal and the measuring diagonal to swap. However, this known possibility of exchange does not indicate the invention, because with the Wheatstone bridge the problem of the contact break at a potentiometer tap and the resulting incorrect measurement does not occur.

The so-called Dießelhorst compensator is also known, the main feature of which is at least consists of a double potentiometer, the taps of which are rigidly coupled to one another. With this well-known The diagonal including the potentiometer taps is also used as a compensator as the feed diagonal used, while the compensation voltage is taken from a diagonal with fixed branch points will. However, the circuit according to Dießelhorst cannot be used for a self-balancing compensator. because for a large range, which is usual with these expansion joints, double potentiometers with strict linearity can only be achieved with great effort.

The bridge circuit according to the invention can expediently be expanded to include a zero point switchover. This is done by the fact that the second branch point of the food diagonal between the Connection points of several bridge resistors can be switched.

The bridge circuit can also be constructed from two potentiometers, the two of which are tapped off Represent the feed points of the bridge. In parallel to each potentiometer, two series-connected Resistances lie. With the help of changeover switches, the supply current from one of the potentiometer taps to the connection point between the two series resistors that are parallel to the potentiometer be switched. Such an arrangement can be used, for example, for an electric weighing device taking into account the tare weight.

Four figures serve to explain the invention.

Fig. 1 illustrates a prior art resistor bridge circuit;

Fig. 2 shows the resistor bridge circuit according to the invention; in the

FIGS. 3 and 4 show expanded bridge circuits according to the invention.

In Fi g. 1, 1 shows a resistance bridge circuit which is connected to a voltage source 2 via fixed diagonal points a, b. A compensation voltage is tapped at diagonal points c and d. The diagonal point d represents the tap of a potentiometer which is moved with the aid of a trimming motor 3. The adjustment motor is controlled via an amplifier 4 from the differential voltage between a voltage U _M to be measured and the compensation voltage U _K. The adjustment motor runs until the tap has reached a position in which the compensation voltage corresponds exactly to the measurement voltage, i.e. the differential voltage controlling the motor at the input of the amplifier has become zero. If the electrical contact at the diagonal point d is interrupted due to contamination or oxidation of the wiper, the motor no longer receives any control voltage. So he remains in the position he has just assumed. This case cannot be distinguished from the comparison case. At the F i g. 1 it can also be seen that contact and thermal stresses at the diagonal point d lie in the compensation circle and can therefore falsify the measurement result.

Fig. 2 shows a self-adjusting compensation circuit using the bridge arrangement according to the present invention. The same components are provided with the same reference symbols in the figures. In contrast to what is known, the resistance bridge arrangement 1 is supplied with a preferably impressed current / via the diagonal points c, d. The compensation voltage, on the other hand, is taken from the diagonal points of the bridge circuit α and b . It can be seen from the drawing that if the contact is interrupted at point d at the input of the amplifier 4, a considerable part of the measuring voltage U _M is present, which drives the motor 3 into an end position, and thus reveals the disturbance present. It can also be seen that the contact and thermal voltages on the wiper are not in the compensation circle and therefore cannot falsify the measurement result.

In Fig. 3, an expanded resistor bridge arrangement is shown. The second feed point can also be switched with the aid of a switch S _2. It is used to change the zero point of the compensator. Another changeover switch S ₁ is used to load the bridge circuit 1 with various load resistances. This measure is equivalent to switching over the measuring range of the compensator. The compensation voltage is taken from terminals α and b.

In Fig. 4, the resistance bridge circuit consists essentially of two potentiometers F ₁ and P ₂ , which optionally form the bridge circuit with series resistors R _v. The taps of the potentiometers P ₁ and P ₂ can be fed by a preferably impressed current / via changeover switches ^ and K _2. The changeover switches can also feed the supply current between two series resistors that are parallel to the potentiometers. The in F i g. The bridge arrangement shown in FIG. 4 is used in an automatic compensator which is part of a weighing device with automatic taring.

Claims (4)

Patent claims: 1. Resistance bridge circuit for generating the compensation voltage for a self-balancing Compensator with at least one potentiometer, whose tap, which can be moved by a balancing motor, is a branch point of the Resistance bridge, characterized in that the compensation voltage from two fixed branch points of one bridge diagonal, while the bridge feed voltage is applied to the fixed Branch point and the potentiometer tap of the other bridge diagonal connected is. 2. Resistance bridge circuit according to claim 1, characterized in that for Purpose of the zero point shift of the compensator the second branch point of the Speisediago- nalen can be switched between the connection points of several bridge resistors. 3. Resistance bridge circuit according to claim 1 or 2, characterized in that for the selection of different measuring ranges different by a switch on the output diagonal load resistances that can be applied are provided. 4. Resistance bridge circuit according to claim 1 or one of the following, characterized ge ίο indicates that the bridge circuit consists essentially of two via its taps of a preferably impressed current is fed potentiometers and the potentiometers two resistors in series are connected in parallel and the supply current can be switched from the potentiometer taps to the connection points of the resistors in series using a switch is. 1 sheet of drawings 509 738 / 1E6 11.65 © Bundesdruckerei Berlin