Polarity reversal procedure

The polarity reversal method is a method from electrical measurement technology for interference suppression in complex impedance measurements with a fixed measurement frequency.

With this method, three measurements are made to determine the impedance of a test object at the measuring frequency:

1. without source
2. with source at measuring frequency
3. with source at measuring frequency, 180 ° phase shifted

Figure 1: Vector diagram for the polarity reversal procedure

Figure 1 shows the complex vector diagram of a voltage measurement with a current fed in on a device under test using the polarity reversal method. Where:

• ${\displaystyle U_{S}}$ a voltage caused by interferers measured with the source switched off,
• ${\displaystyle U_{1}}$ the voltage measured at 0 ° phase shifted source,
• ${\displaystyle U_{2}}$ the voltage measured with the source 180 ° out of phase.

The voltage sought for the impedance determination is calculated from the amounts of the measured voltages according to the following formula: ${\displaystyle U_{M}}$

${\displaystyle U_{M}={\sqrt {{\frac {U_{1}^{2}+U_{2}^{2}}{2}}-U_{S}^{2}}}}$

The impedance can then be calculated using the following formula: ${\displaystyle {\underline {Z}}}$

${\displaystyle {\underline {Z}}={\frac {{\underline {U}}_{M}}{\underline {I}}}}$

When using the polarity reversal procedure, it is important to meet the following criteria:

• The disturbance may only occur at one frequency.
• The disturbance must be stable.

See also

• Interference suppression by the beat method
• Interference suppression with frequency filter

credentials

1. ↑ Power systems with nominal alternating voltages above 1 kV , from VDE standard 0101, VDE classification VDE 0101 , DIN number DIN VDE 0101 , edition 2000-01