Voltage compensation

The voltage compensation method is a method of electrical measurement technology for the currentless measurement of an electrical voltage . One of the variants invented for this purpose is also referred to as a Poggendorff compensation circuit .

Voltage compensator (principle) is adjusted to. Above to Johann Christian Poggendorff , below to Lindeck and Rothe
${\displaystyle U_{K}}$ ${\displaystyle U_{x}}$

function

The circuits work according to the following principle: A compensation voltage is generated, compared with the voltage to be measured and readjusted until equality is established (adjustment). In DIN 1319-2, this method is also called the zero balance measurement method. ${\displaystyle U_{K}}$ ${\displaystyle U_{x}}$

Devices of this type have largely been replaced by electrometer amplifiers or instrument amplifiers with field effect transistors , which can also measure voltages with almost no current. The method continues to be used as negative feedback in electronic circuits.

basis

When matching is

${\displaystyle U_{x}=U_{K}={\frac {R_{1}}{R_{0}}}U_{0}}$

or.

${\displaystyle U_{x}=U_{K}={\frac {R_{1}}{R_{1}+R_{2}}}U_{0}}$

The value of , which can be calculated from the resistances and the supply voltage or, if designed accordingly, can be read directly from the circuit, provides the measured value for . This measurement method avoids any load (current consumption) during calibration. This makes it possible to measure the open circuit voltage even on high-resistance sources. ${\displaystyle U_{0}}$ ${\displaystyle U_{K}}$ ${\displaystyle U_{x}}$ ${\displaystyle U_{x}}$

Precision measurements are possible with a voltage source with a fixed, precise value and digitally adjustable resistors . ${\displaystyle U_{0}>U_{x}}$

The Wheatstone bridge and any other bridge circuit used for measurements also work according to this principle.

Self-adjusting voltage compensation

Basic structure of the self-balancing voltage compensator

With self-adjusting voltage compensation, the voltage difference is not displayed, but instead is increasingly sent to the motor of a motor potentiometer, which adjusts the wiper until the adjustment is achieved. Then = 0; the motor is no longer powered and stops. The grinder is coupled with a pointer in front of a scale so that the measured value can be read immediately . ${\displaystyle U_{d}=U_{x}-U_{K}}$ ${\displaystyle U_{d}}$

The self-adjusting compensator has found widespread use in the compensation measuring recorder , whereby the motor, together with the grinder and pointer, also moves a pen.

The gain factor has no influence on the size of the measuring range , but is essential for the dynamic behavior:

• If the gain is too low, creeping behavior occurs - up to the hysteresis effect due to the motor's response threshold.
• If the amplification is too great, the grinder swings over to the state of undamped oscillation due to the inertia of the mechanical parts.

literature

• Melchior Stöckl and Karl Heinz Winterling: Electrical measurement technology . 8th edition. Teubner, 1987, p. 135 ff .
• Rudolf Holze: Guide to Electrochemistry . 1st edition. Teubner, 1998, ISBN 3-519-03547-2 , pp. 224 to 229 .