LP21/LP22
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LP21/LP22 Installation instructions en
Sensors
4.3.1
Vehicle detection
Whether a metallic object is located in the loop area is identified via an LC oscillator (electrical oscillatory
circuit). The channel output is switched according to the output function configured.
4.3.2
Output signals
Depending on the output configuration, presence, pulse or direction signals and direction logics (LP22) as
well as loop faults are output.
For the pulse signal, it is also possible to select whether an output should occur when a loop is driven past or
vacated.
In addition to inversion of the output signal, both outputs can individually be permanently switched on or off.
4.3.3
Alignment of the loop channels
When the detector is switched on or the reset button on the front is pressed for one second, an alignment of
the loop channels is run.
If there has been an interruption of power, an automatic alignment only takes place if the operating voltage
has been interrupted for at least 0.5 seconds. Alignment takes around one second if no vehicles drive over
the loop in this time.
External influences on the loop frequency may result in longer alignment times, and their causes must be
determined and eliminated.
4.3.4
Scanning of the loop channels
The dual-channel traffic detector LP22 can evaluate two loop channels.
The timed scanning of the loops is carried out in multiplex mode. They are connected to the common
oscillatory circuit oscillator over a multiplexer. This prevents the loops interfering with each other.
The connected induction loops are switched on and off in rapid succession. Current is only ever supplied to
one loop at a time. This means that both loops can be operated at the same frequency.
The cycle time of a scan in multiplex mode is 12 ms.
4.3.5
Loop error detection
Loop closure
and
loop break
are identified as loop errors.
If no induction loop is connected to the loop channel, this corresponds to a
loop break
error status.
Once a loop error has been detected, the loop channel switches off. This may cause the available operating
modes to be restricted, for example direction detection.
