App-34 IM 760301-01E
Appendix 8 Compensation Function
This function compensates for the loss caused by the wiring of each element.
The WT3000 has the following three types of correction functions to measure the power
and efficiency with high accuracy.
• Wiring Compensation
• Efficiency Compensation
• Compensation for the Two-Wattmeter Method
Wiring Compensation
This function compensates for the loss caused by the wiring of each element.
•U – I
This is used when the voltage measurement circuit is connected to the load side.
The measured voltage is determined by subtracting “the voltage applied to the current
terminal” from the voltage value of each element. The voltage applied to the current
terminal is derived by the equation: the measured current × the input resistance of the
current terminal.
SOURCE
LOAD
U
I
I
U
±
±
•I – U
This is used when the current measurement circuit is connected to the load side.
The measured current is determined by subtracting “the current that flows through the
voltage terminal” from the current value of each element. The current that flows
through the voltage terminal is derived by the equation: the measured voltage/the
input resistance of the voltage terminal.
SOURCE
LOAD
U
I
I
U
±
±
• Compensation Details
The measured value is determined by substituting the compensated instantaneous
values u’(n) and i’(n) below into the respective equation in appendix 1.
For U-I Wiring
Compensated instantaneous voltage: u’(n) = u(n) – Ri×i(n)
The instantaneous current is i(n).
For I-U Wiring
Compensated instantaneous current: i’(n) = i(n) – u(n)/Ru
The instantaneous voltage is u(n).
In the equations above,
u(n): Measured instantaneous voltage (sampled data of the voltage signal)
i(n): Measured instantaneous current (sampled data of the current signal)
Ru: Compensation value for the input resistance (10 MΩ) of the voltage input terminal
Ri: Compensation value for the input resistance (5.5 mΩ) of the direct current input terminal
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