Measurement of main circuit voltages, currents, and powers
PRECAUTIONS FOR MAINTENANCE AND INSPECTION
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5
5.2.1
Measurement of powers
Use digital power meters (for inverter) for the both of inverter input and output side.
5.2.2
Measurement of voltages
Inverter input side
Use digital power meters (for inverters) for the input side voltage.
Inverter output side
When using a measuring instrument, use a digital power meter for inverters as the inverter outputs PWM-controlled square
wave voltage. The value monitored on the operation panel is the inverter-controlled voltage itself. Monitoring values via the
operation panel or by outputting the analog signal is recommended as these values are accurate.
5.2.3
Measurement of currents
Use digital power meters (for inverter) both on the inverter's input and output sides.
Since the inverter input current tends to be unbalanced, measurement of three phases is recommended. The correct value
cannot be obtained by measuring only one or two phases. On the other hand, the unbalanced ratio of each phase of the
output side current should be within 10%.
The inverter output current can be monitored on the operation panel. The value displayed on the operation panel is accurate
even if the output frequency varies. Hence, it is recommended to monitor values on the operation panel.
5.2.4
Measurement of inverter input power factor
Calculate using effective power and apparent power. A power-factor meter cannot indicate an exact value.
5.2.5
Measurement of converter output voltage
(across terminals P and N)
The output voltage of the converter is output across terminals P and N, and can be measured with a voltmeter such as a
digital multimeter. Although the voltage varies according to the power supply voltage, approximately 540 VDC to 600 VDC is
output when no load is connected and voltage decreases during driving load operation.
When energy is regenerated from the motor during deceleration, for example, the converter output voltage rises to nearly 800
VDC to 900 VDC maximum.
5.2.6
Measurement of inverter output frequency
In the initial setting of the FM-type inverter, a pulse train proportional to the output frequency is output across the pulse train
output terminals FM and SD of the inverter. This pulse train output can be counted by a frequency counter, or a digital
multimeter can be used to read the mean value of the pulse train output voltage. When a meter is used to measure the output
frequency, approximately 5 VDC is indicated at the maximum frequency.
For detailed specifications of the pulse train output terminal FM, refer to the FR-F800 Instruction Manual (Detailed).
In the initial setting of the CA-type inverter, a pulse train proportional to the output frequency is output across the analog
current output terminals CA and 5 of the inverter. Measure the current using a digital multimeter.
For detailed specifications of the analog current output terminal CA, refer to the FR-F800 Instruction Manual (Detailed).
Total power factor of the inverter
=
Effective power
Apparent power
=
Three-phase input power found by the 3-wattmeter method
V (power supply voltage)
I (input current effective value)
√
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