Eurotherm 7000 Series, Руководство пользователя

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7300A User Manual 5-7
Alarms
5.8. OVER LOAD ALARM (ICO option)
The type 2 alarm (Over-current alarm) monitors the maximum current value.
This alarm (and option) is known as ICO (Intelligent Chop Off).
5.8.1. Availability
The ICO option is available in zero-crossing firing modes (‘Burst mode’ and ‘Single-cycle’)
provided the DLF option is fitted.
The ICO option is not available for short wave infrared elements and transformers (code
SWIR or XFMR), or in control with current limit (code VICL or V2CL).
5.8.2. Alarm conditions
With the ICO option an Over load fault is detected if one of the following two conditions occurs:
• the instantaneous current on one of the three phases exceeds a threshold of 150% of
the instantaneous rated current
• the rms load current (over 5 consecutive seconds) on one of the three phases exceeds a
threshold of 110% of the recalibrated rms current.
The instantaneous or rms current threshold can be adjusted with the ‘I lim’ potentiometer
during the current calibration phase, from 20% to 100% of the nominal current for the
thyristor unit.
5.8.3. Alarm Actions, Memorisation, Acknowledgement
If an over-current alarm is triggered, thyristor firing stops:
• at the end of the half-cycle when the instantaneous current threshold is exceeded
• after approx. 5 s of continuously exceeding the rms current threshold.
Over-current alarm cut-off is signalled as follows:
• the position of the Alarm relay contact changes
• the ‘...ICO’ LED flashes (and turns red).
Important: • The ‘ICO’ LED starts flashing as soon as the rms current exceeds the
threshold; i.e. 5 s before firing may be cut off.
• Setting the Over-current alarm threshold in operating conditions is
described on page 4-4.
Red LED:
'Over-Load alarm'
Alarm threshold
adjustment potentiometer
GRF
DLF
CHK
A
SET
...
ICO
I
LIM
+
Figure 5-3 Layout of the ‘ ICO’ LED and ‘I lim’ potentiometer with the ICO option
The over-load alarm cut-off is memorised.
The thyristor unit remains cut off and signals the alarm status.
The Over-load alarm may be acknowledged by applying +5 V to the ‘ACK’ terminal on the
‘DIG.IN’ terminal block (logic signal inputs). The internal supply (‘5VD’ terminal) or an
external source may be used to acknowledge the alarm remotely.