Beat method

The beat method is a method from electrical measurement technology for interference suppression in complex impedance measurements . Here, a measuring current is fed in, which differs in frequency from the desired frequency and any interference frequencies that may be coupled in, primarily the network frequencies of power supply networks. The name is derived from the physical concept of beat .

The following conditions must be met for interference suppression using the beat method:

• The amplitude of the disturbance must be smaller than that of the quantity to be measured.
• The disturbance may only occur at one frequency.
• The disturbance must be stable.

Impedance measurement on a high voltage cable

Figure 1: Vector diagram of the beat method

In the case of high-voltage equipment , the mains frequency is 50 Hz or 60 Hz, depending on the country.For example, if you want to determine the impedance of a high-voltage cable at 50 Hz mains voltage, you feed in a current with a slightly lower frequency (e.g. 49.9 Hz). In such a case, "interferers" are i. d. Usually high-voltage equipment ( transformers , lines, etc.) that is in the vicinity and in operation , which couple with the mains frequency accordingly. Figure 1 shows a phasor diagram with the voltage vectors in the complex plane, resulting from a current fed in at a measuring frequency. The pointer rotates ("floats") due to the frequency deviation between the measuring frequency and the interference frequency . After a complete suspension period (one revolution of the pointer ), the measurement voltage can be determined from the voltage recorded over time . For this purpose, the maximum amount and the minimum amount are used. The first thing to measure is ${\displaystyle U_{S}}$ ${\displaystyle U_{S}}$ ${\displaystyle U_{M}+U_{S}}$ ${\displaystyle U_{M}}$ ${\displaystyle U_{2}=max\left(\left|U_{M}+U_{S}\right\vert \right)}$ ${\displaystyle U_{1}=min\left(\left|U_{M}+U_{S}\right\vert \right)}$ ${\displaystyle {\underline {U}}=U_{M}+U_{S}}$

A distinction must be made between two cases:

• ${\displaystyle U_{S}<U_{M}}$ : ${\displaystyle U_{M}={\frac {U_{1}+U_{2}}{2}}}$
• ${\displaystyle U_{S}>U_{M}}$ : ${\displaystyle U_{M}={\frac {\left|U_{1}-U_{2}\right\vert }{2}}}$

The impedance is determined using the formula ${\displaystyle {\underline {Z}}={\frac {{\underline {U}}_{m}}{\underline {I}}}}$

The generation of the necessary electricity is usually carried out with diesel generators, since with these the frequency can easily be varied within a small range.

See also

• Interference suppression with the polarity reversal 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