Mitsubishi Electric Melsec Q Series User Manual page 120

9 Troubleshooting
If a load such as welding equipment exists, a current flows only for a short period (e.g.
Q 2-cycle waveform of commercial frequency (50 Hz: 40 ms, 60 Hz: 33 ms)). Is accurate
measurement possible?
This module makes measurement with a sampling period of 4340 Hz (for both 50 Hz and
60 Hz). However, measuring part of buffer memory data (Un¥G100 to Un¥G2999) is updated
every 250 ms. The electrical amount such as current, voltage, electric power, power factor, and
frequency is measured in a cycle of 250 ms period.
A
It is impossible to measure the instantaneous short–term amount of electricity. The amount of
electricity and reactive power amount are measured separately from the momentary data
described above, using a sampling period of 4340 Hz continuously without intermittence.
Therefore, measuring the load for a short period is possible.
Q Obtained values may be different from other measuring instruments. Why is it so?
There are various possible causes. Check the following first, please:
[1] Check for wiring errors (polarity of current sensors, connections of current circuits, and
connections of voltage circuits, in particular).
[2] On the split-type current sensor, check for the poor engagement or separation of fitting
surfaces.
[3] On the split-type current sensor, check for pinching of foreign object between fitting surfaces.
A
[4] Check that the measuring instrument used for comparison indicates a correct RMS value.
[5] If the measuring instrument used for comparison measures an average value instead of rms
value, distortion in the current of the circuit to be measured causes a significant difference of
values. This module measures an rms value.
[6] Check for the short-circuit on the secondary side of the current transformer (CT).
[7] Current sensor connectable to the module is the dedicated current sensor only. Check that
the proper current sensor is connected or not.
9.3.2 Q&A about Specifications
Q
What accuracy does "measuring accuracy" mean?
In terms of the amount of electricity, it means a range of tolerances in reading values. For
example, when the reading value is "10 kWh," a tolerance is ±0.2 kWh.
A
In terms of measuring elements other than the amount of electricity, it means tolerance for the
rated input. For a current, when a rated current is set to 250 A, ±1 % of 250 A is a tolerance.
Q
Is accuracy of a current sensor included?
Accuracy of a current sensor is not included in accuracy of the module.
A
A maximum value of tolerance is obtained by summing tolerance of the module and that of a
current sensor.
Q To what degree an area of microcurrent is measured?
A current value is measured from the area exceeding 0.4 % of the rated current. In an area
below 0.4 %, measurement result is indicated as "0" (zero).
A However, in that case, still, the amount of electricity is being measured. Even if the indicated
value is "0," measurement value will increase in continuing measurement for a long time.
The amount of electricity is measured with a load that is about 0.4 % or more of all load power.
9 - 8
QE81WH