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It is perhaps fitting to launch the “return” of AVO-Megger to the forefront of Telecommunications Industry testing equipment by way of the official announcement of the new Megger BTDR1500 combination test instrument for the field technician.
An advanced and simply-operated unit, the BTDR1500 offers in one compact and modestly-priced IP54 package no less than the five instrument functions of TDR, automatic resistance bridge, insulation tester, loop resistance meter, and voltmeter. Operator prompting is even included to warn of inadequate loop and insulation values if they are detected.
Designed to be used in the first line of defence when uncovering transmission-related problems, the BTDR1500 provides fast and accurate cable fault location results with impressive range and performance. Diagnosis of situations such as Bridge Taps and splices, the presence of water in cables, opens or shorts in A, B, & Earth ( Tip, Ring, and Sheath ), Capacitive Networks, load coils, wet and high resistance splices all present no problem to this instrument.
The set is suitable for locating faults on all types of communication cables including twisted pair, coaxial, parallel conductor, and concentric neutral.
Of major interest in the market, the BTDR1500’s fully-featured packaging of multiple test functions permit the simple determination of how well the local loop could reject common mode noise. As is well known in the Industry, the performance of xDSL and other digital lines is greatly affected by signal attenuation and signal cancellation due to reflections, unbalance, cross talk, and random electrical noise from the surrounding environment. When a circuit has a problem with its balance to ground and resultant signal attenuation on one leg, common mode noise rejection is greatly compromised and indeed then readily translates into destructive differential noise. Collectively, such line problems will result in compromised transmission distances, or possibly increased error rates and reduced transmission speeds. Given the avalanche of pressures on the Industry to furnish high performance data lines and high speed internet access, the advent of the BDTR1500 and its ability to perform balance checks and determine the potential effect on xDSL services is very timely indeed!!
Looking now at the specifications and features of the component testing parts of the BTDR1500, let us begin with the TDR facility itself. Location of open circuits and low resistance faults using this facility can be performed over a range of 0.1m to 3000m to a measurement accuracy of 1%. In the event of a fault close in, a “Tx Null” balance control facility ( 0-120 Ohms ) ensures that the swamping associated with the output pulse is eliminated from the displayed waveform. Pulse widths from as little as 7nS permits accurate fault discrimination on near faults whilst pulse widths of up to 3000nS, in tandem with a variable gain facility, permits even more minor faults to be identified over the entire cable length. Range and gain are automatically selected in accordance with cursor position for optimum display resolution, with manual override offered for each parameter.
In the Automatic Resistance Bridge mode, the BTDR1500 runs through a series of tests to calculate the resistance to a fault. This measurement is made to the far end where a strap has been fitted. Given that the location of the fault will be the point of lowest insulation resistance, the set first performs an insulation test ( 100V dc nom., 0.01-199.9 Megohms ). An operator alert is displayed if the insulation is either below 1 Megohm (“line is bad”) or between 1 and 10 Megohm (“line is fair”). It then performs a loop test to measure the total resistance of the cable loop under test: in this regard, the set has a massive range, coping with a total loop resistance of up to 2000 Ohms ( equating on some cable types to up to 100 km!!). A warning to the operator is provided if loop resistance is over 1000 ohms.
Following the loop resistance test, the BTDR1500 then injects a current through the fault resistance to measure and derives the following: Resistance to Fault ( RTF), Resistance to Strap ( RTS ), and Resistance of the Strap to Fault ( STF ). From the measured resistance values, and by knowing the conversion factors for the gauge of wire ( pre-programmed but customisable ) and its temperature ( entered by operator from a default value ), the distance to fault is calculated and displayed as: Distance to Fault ( DTF ), Distance to Strap ( DTS), and Distance of the Strap to Fault ( STF ). Bridge measurement accuracy is 0.2% and locations can be achieved with high resistance faults up to 20 Megohms!!.
In addition to the TDR and Automatic Resistance Bridge, the BTDR1500 has a voltmeter range for measuring DC voltage to +/- 250 V and can verify if a telecom cable has a Telecom Network Voltage ( TNV) present on it.
Completing this impressive package, the meter itself is housed in Megger’s latest IP54 ABS case design featuring a Mil spec. drop and bump test capability to 40G’s. A backlit LCD ensures effective operation in all conditions ( -15 to +50 Deg C ), whilst a very high quality padded test and carry case with its own protective clear window, shoulder strap, and lead compartment provides an excellent accompaniment.
Due to the design integrity and attention to detail, this outstanding field instrument is supported with a comprehensive three year warranty!!
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