levr
LIM-05 user manual
Dated 25/5/2017
http://www.levr.pl/
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Production of preinsulated pipes with sensor wires ensures good reproducibility of the
product both in terms of the physical properties of materials and reliable geometrical
dimensions. This ensures that certain electrical properties are reproduced in all
products. One of the electrical quantities characteristic to district heating pipelines is
characteristic impedance, amounting to approximately 200
Ω
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measured between the carrier pipe and the copper sensor wire. It should be emphasised
that impedance does not depend on the length and diameter of the district heating
pipeline. However, it may change due to: local change of the distance between the
copper wire and the steel pipe, appearance of moisture in polyurethane insulation,
incorrect connection or a break in the detector line. These cases are regarded as faults
that should be located and eliminated. Faults are located using a reflectometer.
Measurement with this instrument requires generation of a very short electric pulse. It
is transmitted between the copper wire and the steel pipe. Since the characteristic
impedance of the measured circuit is constant, the electric pulse moves freely along the
tested pipeline with speed almost equal to the speed of light propagation. If one of the
indicated faults occur at some point of the preinsulated district heating pipeline,
resulting in the abrupt change of characteristic impedance, the measurement pulse will
be fully or partially reflected. The reflectometer measures the time from the sending of
the electrical signal until its reflection returns. Then, using the entered value of
measurement pulse speed and the measured time, it calculates the distance between the
measurement station and the point of reflection, i.e. location of the fault.
The method of fault location in preinsulated district heating pipelines with a detector
loop described above is implemented using the LIM-05 instrument.
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The LIM-05 fault locator is a stationary instrument. It can be used to monitor four
sections of the district heating pipeline with a pulse alarm system at the same time. The
monitored section of the sensor wire should not be longer than 2500 m. The
measurement result is presented on a graphical display in the form of an annotated
chart. The result is created based on the difference between the previously recorded
reference run and the chart depicting the current condition. Until a fault is detected, the
chart is a straight line (axis x). Axis x is scaled in units of length [m]. The reference
runs for each monitored section of the network are recorded automatically in the
digital memory of the instrument shortly after the operator initiates the measurement
procedure. During initial calibration of the instrument, the length of axis x on the chart
is adjusted to be a precisely proportionate representation of the length of the monitored
section of the district heating pipeline. Information about the fault, in turn, has the
form of a representation of the reflected measurement pulse depicting its actual
electrical shape. The location (above or under axis x) of the reflected pulse and its
shape indicate the type of the fault (e.g. leak, electrical short circuit of the sensor wire
with the steel pipe) and its intensity. The intensity/degree/size of the fault is
represented by the amplitude (height) of the reflected pulse. The amplitude is
measured in units of voltage [mV] and [V]. Axis y is scaled in these units by default.
The distance from the beginning of axis x (x = 0) to the beginning (front) of the pulse
is proportionate to the distance between the beginning of the district heating pipeline
