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V01.00 | 2021/06
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4.3
Operating principle
The expansion module measures the currents of the connected current sensors and outputs
the signals preprocessed to a cabinet guard.
4.4
Functions and operating modes
The device processes the signals of up to twelve AC current sensors and measures the signal
frequency of the sensors. The information is transferred to the IM18-CCM50… cabinet guard via
the backplane bus. The power supply of the device is also implemented via the backplane bus
connector. The configuration of the measurement channels is saved internally and is also re-
tained after the power supply is interrupted.
4.4.1
Current measurement
The current value is shown as an RMS value. The duration of a period is calculated from the con-
figured or measured frequency of the channel. All channels are measured in sequence from
channel 1 to channel 12. Channels that are switched off are skipped.
Each current measured value is output with a time stamp in ms. The maximum value of the
time stamp is 59999 ms.
Measurement duration
A measurement starts at a zero crossing of the input signal and lasts for a full period. If a zero
crossing is not detected, the device ends the measurement after max. 112.5 % of the previous
period duration.
The maximum duration of a measurement is 0.5 × T + 1.125 × T = 1.625 × T.
4.4.2
Frequency measurement
The device makes it possible to measure the frequency of the measured signal. This requires
the reference frequency to be set in the device. The frequency is measured if the measured fre-
quency signal is above or below the reference frequency by a maximum of 12.5 %. The meas-
ured frequency is used as a time base for the current measurement. If a valid frequency is not
measured, the device outputs a value of 0 Hz.