Measurement Of Voltages And Use Of Pt; Measurement Of Currents; Use Of Ct And Transducer; Measurement Of Inverter Input Power Factor - Mitsubishi Electric 800 Series Instruction Manual

3.2.2

Measurement of voltages and use of PT

 Inverter input side
Use a digital power meter (for inverter) on the inverter's input side.
 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.
3.2.3

Measurement of currents

Use a digital power meter (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
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.
3.2.4

Use of CT and transducer

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
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.
3.2.5

Measurement of inverter input power factor

Calculate the factor from the effective power and the apparent power. A power-factor meter cannot indicate an exact value.
Total power factor of the inverter =
3.2.6 Measurement of converter output voltage (between
terminals P and N)
The output voltage of the converter can be measured with a voltmeter (such as a digital multimeter) between terminals P and
N. The voltage varies according to the power supply voltage. Approximately 270 to 300 V for the 200 V class, approximately
540 to 600 V for the 400 V class, and approximately 800 to 900 V for the 575 V class is output when no load is connected. The
voltage decreases when a load is applied.
When energy is regenerated from the motor during deceleration, for example, the converter output voltage rises to nearly 400
to 450 V for the 200 V class, nearly 800 to 900 V for the 400 V class, and nearly 1100 to 1300 V for the 575 V class maximum.
3.2.7

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 on 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 digital multimeter 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-E800 Instruction Manual (Function).
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3. Precautions for Maintenance and Inspection
3.2 Measurement of main circuit voltages, currents, and powers
Effective power
Apparent power
Three-phase input power found by the 3-wattmeter method
=
√
3×V (power supply voltage) × I (input current effective value)