DigiTrace DET-3000 Краткое справочное руководство - Страница 2
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Печатать страницу1. DET-3000 cable fault locater
The DET-3000 cable fault locater can be used to locate many types of electrical fault to almost
any type of electrical cable, including heating cables, caused by mechanical damage during
installation, maintenance and use. The DET-3000 quickly and easily locates these spots of trou-
ble without requiring the high cost of thermal insulation removal and replacement. The dam-
aged section of cable can be repaired with a minimum of disruption to the remainder of the
installation. The DET-3000 is shipped in a rigid carrying case and comes complete with 100
Ohms test leads preinstalled and an extensive user manual. The DET-3000 uses the principle of
time domain reflectometry (TDR) to locate cable faults. The DET-3000 can locate major or
minor cabling problems including; sheath faults, broken conductors, water damage, loose con-
nectors, crimps, cuts, smashed cables, shorted conductors, system components, and a variety
of other fault conditions. In addition, the DET-3000 can also be used to assist in inventory man-
agement to test reels of cable for shipping damage, cable shortages and cable usage. The speed
and accuracy of the DET-3000 makes it the preferred method of cable fault location.
The DET-3000 cable fault locater is derived from the Bicotest limited Lexxi™ T810 cable fault
locator. As such all user recommendations and technical specifications listed in the Bicotest
Lexxi™ T810 user manual (00901274-2) are applicable to both product types. Tyco Thermal
controls will not supply any of the accessories listed in that manual. DET-3000 is a trademark of
Tyco Thermal controls. Lexxi is a trademark of Bicotest Limited.
2. Principles of operation
Time domain reflectometers, such as the DET-3000, work on the same principle as radar. A
pulse of energy is transmitted down the cable. When that pulse reaches discontinuity, such as
the end of the cable, or a fault along the cable, part or all of the pulse energy is reflected back
to the instrument. The DET-3000 measures the time it takes for the signal to travel down the
cable, see the discontinuity, and reflect back. The DET-3000 then converts this time to distance
and displays the information as a waveform and/or distance reading.
3. Impedance
Any time two metallic conductors are placed close together, they form a cable impedance. The
DET-3000 looks for a change in impedance which can be caused by a variety of circumstances
such as: cable damage, water ingress, change in cable type, improper installation, and even
manufacturing flaws.
The insulating material that keeps the conductors separated is called the cable dielectric. The
impedance of the cable is determined by the spacing of the conductors from each other and the
type of dielectric used.
The DET-3000 sends electrical pulses down the cable and samples the reflected energy. Any
impedance change will cause some energy to reflect back toward the meter and will be dis-
played. How much the impedance changes will determine the amplitude of the reflection.
4. Propagation velocity factor (pvf)
The DET-3000 is an extremely accurate instrument. However, variables in the cable itself or the
path along which the cables are laid out sometimes cause errors in distance measurements.
One way to minimize error is to use the correct Velocity of Propagation (pvf) of the cable under
test. The pvf is a specification of the cable indicating the speed at which a signal travels down
the cable. Different cables have different pvf. In order to assure the most accurate distance
measurements the cable pvf must be known.
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