DE1591988C - Circuit arrangement for converting a detuning of a resistance bridge into a proportional frequency change of an RC oscillator - Google Patents

Description

In this case, a voltage Uy derived from the bridge supply voltage U _s via the operational amplifier OV, which is connected to the fixed feedback resistor R ₀ and the input resistor R ₁ that can be changed by the compensation amplifier, determines the differential voltage

In this way, the desired proportionality between the conductance of the amplifier input resistance J ?! and the bridge upset reached. The voltage U _v at the output of the operational amplifier OV is a linear measure for the bridge detuning. The resistor R ₁ is now at the same time part of the frequency-determining network of an RC oscillator OS ₃ , the side of the resistor H ₁ facing the operational amplifier being practically at reference potential, since the operational amplifier generally has a high gain. Such an oscillator can be a known .RC oscillator with a frequency-determining network of two resistors and two capacitors, of which the first resistor can be changed from the outside, while the second resistor is electronically tracked to the changes of the first resistor to maintain a stable oscillation. In place of the externally changeable resistance, the direct or reciprocal proportional resistance of the bridge detuning can be used, whereby the supply voltage for the bridge can be taken from the oscillator at the same time, while the resistance R _{1 is} not directly but via the frequency-determining network this supply voltage is connected.

1 sheet of drawings

Claims (1)

1 . 2 a bridge through a compensation amplifier Claim: · ■ also derives a change in resistance. This However, change in resistance is not evaluated Circuit arrangement for converting a and also no possibility for it specified or Detuning from a voltage source 5 is indicated. The object of the invention, on the other hand, is to convert a level into a proportional frequency bridge detuning into a proportional frequency change of a jRC oscillator, the frequency change being converted. This output terminal of the bridge with the input would be solved by the fact that one of the output terminals of the terminals of a compensation amplifier is connected, the bridge is also connected via a resistor to the one whose output voltage is a control output of a resistor in a known manner directly or indirectly provided coupling resistance operation-taxed, characterized in that the amplifier is connected, the input of which is connected via the one of the output terminals of the bridge also controllable resistor to the voltage source via a resistor (R _P1 ) with the output 15, and that the controllable Resistance of a known manner with a negative feedback component of the frequency-determining network treatment resistance (R ₀ ) provided operation-Ver of the KC oscillator is. stronger (OV) is connected, whose input via This frequency change can easily be the controllable resistance (R ₁ ) to the span _{: transfer} larger distances and is special power source (U _s ) is connected, and that the 20 is insensitive to interference, controllable resistor (R ₁ ) part of the fre- An embodiment of an inventive The figure shows the sequence-determining network of the jRC oscilloscope arrangement. This contains a cons lators is. "'Stand bridge with bridge resistors R _B i, R _B2 , Rb3 and R _BA ., which are fed from a voltage source U _s 25 and whose output terminals are connected to the input terminals of a compensation amplifier V. The output of the compensation amplifier The invention relates to a circuit arrangement kers V is with an energy source L, z. B. one for converting a detuning from an incandescent lamp connected, the light of which is fed to a control voltage source resistor bridge with ₃₀ baren resistor R ₁ , z. B. a photoresistor, four resistors in a proportional Fre- falls. This controllable resistor R ₁ is connected to a change in frequency of an ÄC oscillator, the output end being connected to an energy source, in the shown Ausfühgangsklemmen the bridge with the input terminals approximately example on the energy source U _s , and to that of a compensation amplifier, the other end are connected at the input of an operational amplifier output voltage a controllable resistor 35 kers OK, which controls in a known manner with a feedback or directly. Lead resistance R _{0 is} bridged. In addition, the output terminals is on for a series of Meßaufnahmen to Umfor- the bridge circuit, the mung physical quantities into electrical quantities series connection of a further resistor R _Pl, the reproduced value to be measured by only a very small of the output of the operational amplifier OV and relative effect of a resistor . 40 of a resistor R _P0 . An example of such sensors are strain gauges. If the resistance bridge is in equilibrium, there are measuring strips. With the help of bridge circuits, 'z. B. all bridge resistances are the same
generally the resistance misalignment in a to / " _ _R _ η _ _R - 1? \
proportional voltage transformed, however, because of- I si - bi - bs - b4 - b;>
the only small change in resistance corresponding to 45 then the bridge output voltage U _B = O. A is low. In practice, the further modification of one or more bridge reworking of the output voltages of such bridge statuses has a voltage at the output of the re-connections, but has considerable difficulties. In many cases, the result is a bridge. If, for example, all det you are using compensation measuring devices in which four bridge resistances are detuned, in such a way that
the bridge output voltage, for example, from 50 R = R = R + AR (1)
an electromechanically variable second counter.
compensation voltage derived from the stand bridge is switched against and the · detuning of this ^ ^ß 2 = ° b3 = Rb ~ second resistor bridge as a measure of the, _{then detuning the output voltage of the} resistor measurement of the measuring bridge is displayed. With the ver 55, .., ° ^r Mood Mechanism of the Second Resistance ^ ^ bridge is often mechanically a so-called follow-up U _B = U _s . (2) potentiometer coupled whose detuning ^B the second resistance bridge and thus to this voltage is after in a known manner Detuning of the measuring bridge proportional resistance measured 60 the compensation principle by its one stand or attenuation factor can also be easily switched against via variable compensation voltage greater distances can be measured. After- and by changing this voltage, the difference Part of such compensation measuring devices is their difference between the two voltages being made zero large space and power requirements and in particular will. those working with mechanically moving parts 65 The input variable of the compensation amplifier devices own susceptibility to interference. kers V, which provides the on-off position of the resistor R ₁ via the energy source L for the on-off position of the resistor R 1, the bridging arrangement is known, which derives from the detuning of the output voltage.