The differential pressure (does not apply to devices with pure time control) is measured
externally and passed on as a 4…20 mA signal to the control. The signal can be con-
nected to both the master, as well as to one of the extension units. In addition, there is
the possibility that the 4…20 mA signal can be connected to an external dis-play device.
To do that, the display device is switched corresponding to the connection plan in se-
quence with the differential pressure transducer (e.g. HE 5409), (see position 1 in Figure
21 or Figure 22). If a galvanic separation is required, an isolation amplifier (e.g. HE
501/HE 502) must be used.
Cleaning process
The cleaning process is started in normal operation, when the upper limit is exceeded,
and ended when the lower limit, “cleaning”, is reached. During activated precoating func-
tion the de-dusting at the upper threshold that is increased by the precoating offset starts.
There is a delay time of 5 minutes to carry out purification during a normal shut-off pro-
cess, without triggering an alarm warning of the low alarm. The purification limit must be
reached before the end of the 5 minutes; otherwise, the low alarm is triggered.
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