9 | Maintenance
92
D-LX 201/721
stopping the supply voltage, e.g. by disconnecting the red 24V supply line. This saves
the operator having to open the cover. Alternatively, an external reset can be per-
formed via the "External reset" contact (on the device cable). Only perform a reset
● After the cause of the fault has been rectified
● If the system status is identifiable
● If the information necessary for the process being controlled is known.
Regardless of the device status (flame ON/OFF signal or fault), the relays will be de-
activated following a mains interruption or after the internal reset button is pressed,
and the flame monitor program will restart.
NOTICE
The flame monitors (including the Ex versions and all associated components) are
devices with type approvals.
Any changes to to devices with type approvals will lead to the loss of the approval.
Repairs must only be performed by the manufacturer or persons that it has authorised
to do so. This is the only way of ensuring responsible compliance with the
specifications for the type approval of the certifying body.
9.5.2 Warning in the event of different switch positions
If the switching threshold or amplification characteristic settings are different for the
two flame monitor channels (see also section 8.1 Range selection [}72] und 8.3 Se-
lecting the gain characteristic curve [}75]), then the "Switch error" LED on the back of
the device (see Fig.6.7 in section 6.2.4 Front panel (all types) [}49]) will light up red. If
this difference remains in place for more than 8 secs, an error shutdown will be per-
formed (see also the table on page [}49]).
9.5.3 Harmonic detection
The flame monitor can perform a harmonic detection [}115]. This involves the flame
monitor monitoring the behaviour of the measured flicker frequency over time. The
flicker frequency of a firing process will always fluctuate. If a constant flicker frequency
is detected for several seconds, this may indicate an artificial light source, for ex-
ample. Harmonic detection ensures that artificial light sources cannot be classed as
flames by the flame monitor.
If a constant frequency is measured for more than 10 secs, the flame monitor will re-
port:
● "Flame OFF"
● The "Freq" LED on the back of the device flashes
● The value of the analogue output remains constant at 4 mA/7.2 mA.
When using the D−LX 201 InformationCentre [}115] (Flame information window):
● The "Analogue output" bar remains at 20%.
● The "Harmonic frequ." field is active (green).
Harmonic detection is deactivated when the frequency switching threshold is set to 0
(zero).
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