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The external NTC temperature sensor
21
cuit
, which produces the bias voltage for this NTC and is simultaneously controlled and
monitored by the µP. The signal from the NTC temperature sensor is taken via the filter
the A/C converter of the µP. This filter reduces electromagnetic interference and protects
the circuit against electrostatic discharges (ESD)
The µP
1
communicates via the line interface
Through the data interface
modes, initiate diagnostic steps, etc. Response signals, results from diagnostic inquiries,
and status signals are transmitted by the detector back to the control unit.
To prevent total bus failure in the event of a short circuit, DOT1152 disconnector detectors
can be installed which «isolate» defective sections. In the DOT1152 disconnector detector
two «electronic switches» (FET)
isolate the faulty section of the line until the short circuit is remedied.
17
The driver
for the response indicators (RI) activates the blinking of the internal RI
an external RI
19
under control of the control unit.
5
Self-test / function state
Periodically and on request by the control unit a comprehensive detector self-test is initi-
ated which monitors the IRED current, the signal amplifier and the EEPROM.
Also periodically monitored are the compensation value, NTC, the line voltage, etc. The
entire signal path is monitored with the compensation value. If the basic pulse value is too
low, this condition is signalled.
If the detector signals a status change, the control unit can read the cause out of the detec-
tor memory.
«Function state 0» corresponds to «Normal state».
In the «Normal state» the detector is fully functional.
«Function state 1» corresponds to «Notices».
«Notices» draw attention to certain irregularities, for example, error ID-ROM, but these do
not influence the correct functioning of the system.
«Function state 2» corresponds to «Impairment».
«Impairments» are not accurately quantifiable deviations of the system (for example, com-
pensation value too high). The reasons leading to the response of the detector must be
taken seriously.
«Function state 3» corresponds to «Fault».
A «Fault» is an impairment of such a serious nature that the response of the detector can no
longer be taken to signal a real event but the fault must be immediately remedied.
Compensation range
Voltage in-
crease for
detection
Fig. 4
Compensation range
22
is controlled by circuit element
14
and the two-wire bus with the control unit.
15
the detector receives commands that activate the operating
16
open automatically in the event of a short circuit and
Upper limit value (function state 2)
Drift (function state 1)
Basic detection pulse, new condition
Lower limit value (function state 1)
Zero value
23
. It contains cir-
20
to
18
and
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