9
Troubleshooting
QE81WH4W
Q
If a load such as welding equipment exists, a current flows only for a short period (e.g.
2-cycle waveform of commercial frequency (50 Hz: 40 ms, 60 Hz: 33 ms)). Is accurate
measurement possible?
A
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.
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?
A
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.
[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?
A
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.
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 and the voltage transform unit included?
A
Accuracy of a current sensor and the voltage transform unit are not included in accuracy of the module.
A maximum value of tolerance is obtained by summing tolerance of the module and that of a current
sensor and the voltage transform unit.
Q
To what degree an area of microcurrent is measured?
A
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).
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.
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