Biddle CFL510F_UG 电路图.pdf

CABLE FAULT LOCATOR MEGGERCFL510F (TDR1000/2) User Guide MEGGER RadioFans.CN 收音机爱 好者资料库 RadioFans.CN 收音机爱 好者资料库 SAFETY WARNINGS Although this tester does not generate any hazardous voltages, circuits to which it can be connected could be dangerous due to electric shock hazard or due to arcing (initiated by short circuit). While every effort has been made by the manufacturer to reduce the hazard, the user must assume responsibility for ensuring his, or her own safety. For use on energised systems rated up to 300V Installation Category III* the fused clip set AVO Part Number 6111-218, must be used. * Relates to the transient over voltages likely to be met in fi xed wiring installations. 4mm plug to BNC Adaptor: This 4mm plug to BNC adapter is intended for use with telecomm network cables only, it is not designed or intended for direct connection to an energised mains supply. However, in normal use it may be subject to telecom network voltages (TNV) as defi ned by IEC 60950 3rd edition (1999-04). The BNC plug and socket are, by necessity, accessible. The outer sheath for this connector is normally at SELV levels, however under single fault conditions it may carry hazardous voltages. The operator must therefore verify that the accessible plug or socket is at SELV levels prior to touching, or alternatively wear appropriate insulated gloves. The instrument should not be used if any part of it is damaged. Test leads, probes and crocodile clips must be in good order, clean and with no broken or cracked insulation. Check that all lead connections are correct before making a test. A Fused Lead Set must be used to connect to energised live systems. Refer to the accessories section for options. Disconnect the test leads before accessing the battery compartment. Refer to operating instructions for further explanation and precautions. Safety Warnings and Precautions must be read and understood before the instrument is used. They must be observed during use. 3 NOTE THE INSTRUMENTS MUST ONLY BE USED BY SUITABLY TRAINED AND COMPETENT PERSONS. RadioFans.CN 收音机爱 好者资料库 Contents Safety Warnings3 Introduction5 General description Battery replacement User Controls and Display8 Layout and functions Operation10 General Testing procedure Line Feed Connection to cable under test Measuring distance to fault Menu TX Null Velocity Factor Pulse widths Techniques to improve accuracy Care and Maintenance15 Specifi cations16 Symbols used on the instrument are: Caution:Referto accompanying notes. Equipment protected throughout by double or reinforced nsulation. Instrument fl ash tested to 3.7kV rms. Equipment complies with current EU directives. 4 Introduction Thank you for purchasing the CFL510F cable fault locator. Before attempting use of your new instrument please take the time to read this user guide, ultimately this will save you time, advise you of any precautions you need to take and could prevent damage to yourself and the instrument. The CFL510F is an advanced instrument capable of identifying a wide range of cable faults. The instrument uses a technique called Pulse Echo (also known as Time Domain Refl ectometry or TDR). A pulse is launched into a cable from one end. This can be on either a pair of conductors, or a conductor and the screen. The pulse travels down the cable at a velocity determined by the insulation between the conductors and this resistance to the fl ow of the pulse is characterised as impedance for the cable. Any changes in cable impedance will cause a proportion of the pulse to be refl ected. The pulse velocity is normally described as a fraction of the speed of light and is called the Velocity Factor. By measuring the time between the transmitted pulse and the reception of the reflected pulse, and multiplying this by the speed of light and the velocity factor, the actual distance to the refl ection point can be established. Refl ections are caused by changes in the cables characteristic impedance, such as poor joints or discontinuities. Faults showing an impedance higher than that of the cables normal impedance will cause a refl ection of the same polarity, i.e.positive, whilst faults with an impedance lower than that of the cable will cause an inverse negative going reflection. Matched cable terminations absorb all the pulse hence no “end of cable” refl ection will occur, the cable appearing endless. Open or short circuits will refl ect all the pulse and a large refl ection will be displayed. At an open or short circuit all the transmitted energy is refl ected and the TDR will not see the cable beyond that fault. As a pulse travels down a cable, the size and shape of that pulse is gradually attenuated by the cable. The pulse reduces in amplitude and becomes more elongated or stretched. The level of attenuation (or losses) is determined by the cable type, the condition of the cable and any connections along its length. The limit of how far you can see is determined by the point beyond which you will not be able to see or distinguish a reflection. To help identify small reflections, especially at greater distance the CFL510F has an adjustable gain setting. By increasing the gain small refl ections become more obvious. The CFL510F can be used on any cable consisting of 5 Introduction at least two insulated metallic elements, one of which may be the armouring or screen of the cable. The CFL510F has internal matching networks to allow testing of 25, 50, 75 and 100 cables. (These typically correspond to power, coaxial data and data/telecoms cable). By selecting the TDR impedance closest to that of the cable under test, maximum power can be transmitted into the cable allowing long cables to be tested. The velocity factor of the TDR must be adjusted to match that of the cable under test, allowing an accurate distance measurement to be read directly from the instrument. Where the VF of a cable is not known, but the length is, the cursor can be set to the end of the cable and the VF on the TDR adjusted until the correct cable length is displayed. Other confi guration settings include changing the distance units between metres and feet, changing the propagation velocity units between a ratio and a distance per microsecond. Display contrast is fully adjustable to compensate for all viewing conditions. A backlight aids viewing in low ambient light conditions. The instrument can be powered by manganese- alkali, nickel-cadmium or nickel-metal-hydride batteries. All cells must be of the same type. 6 When the low battery symbol appears in the display window the cells are nearly exhausted and should be replaced as soon as possible. Use alkaline cells IEC LR6 (AA) 1.5V or 1.2V rechargeable cells only. To install or replace the cells, switch the instrument off. Disconnect the test leads, loosen the battery cover retaining screws and remove the cover. Lift out and disconnect the battery holder. Replace the cells, ensuring that correct polarity is observed (shown on the battery holder). Incorrect battery cell polarity can cause electrolyte leakage resulting in damage to the instrument Refi tting the battery holder is the reverse of removing it. 7 Battery fi tting and replacement User controls and display 8 The controls of the TDR have been arranged such that the instrument is easy to learn and use. The instrument controls consist of the following Instrument Display: The display shows the user the current settings of the instrument and the refl ected energy trace from the cable connected. Tx Null: This rotary control allows the user to match the internal balance circuit of the TDR to that of the cable under test. When correctly adjusted the majority of the displayed transmitted pulse can be nulled out, allowing cable features close to the start of the cable to be identifi ed. Refer to section TX Null for further details. Cursor Left: Moves the distance cursor to the left. Auto repeats if held down. Cursor Right: Moves the distance cursor to the right. Auto repeats if held down 3000m1780m75 0.67R Transmission pulse Range Distance to cursorImpedance Gain Refl ection 9 User controls and display Find key:Automatically moves the cursor to the fi rst potential fault (change of impedance). Power: Pressing this button will turn the instrument on or off depending on its current state. Range: A bi-directional button allowing range adjustment from 10m (30ft) to 3km (10 000ft) in 6 steps. The bi-directional feature allows ranges to be selected forward and backward, without having to scroll through all the ranges in one direction Gain:This control is used to increase or decrease the gain of the instrument. This helps the user identify faults over the entire cable length. Velocity Factor: Adjusts the Velocity Factor (VF) of the instrument to match that of the cable under test. IMPORTANT: The VF value must match the VF of the cable under test to give an accurate distance measurement. Menu: Allows the user to change the units of measurement for Distance, Velocity Factor, Impedance and Test Rate. Refer to menu section later in this text. Backlight: Pressing this button will toggle the backlight on and off. The backlight will automatically switch off after 1 minute Contrast: Allows the user to manually correct the display contrast to suit local ambient lighting conditions. Output Sockets: 4mm shrouded sockets designed to accept the leads supplied with the instrument. Battery cover: Located on the back of the instrument and provides the user with access to the battery compartment. The cover must not be removed while the instrument is switched on or connected to a cable. The instrument must not be operated with the cover open. Operation 10 General Testing procedure Ensure the correct test leads are fi rmly fi tted into the sockets of the instrument. Switch on the instrument. The CFL510F will display the start screen for a couple of seconds, followed by a trace. The instrument will be set to the range and velocity factor last used. If these settings are different for the cable under test (C.U.T) then use the RANGE and VF keys to set the correct values. Refer also to Velocity factor later in this text. Connection to Cable Under Test Connect the test lead to the cable under test. Connection may be made to a live system with a voltage to earth (ground) less than 300V with an installation (over voltage) category of III or lower. This means that the instrument may be connected to any fi xed wiring of a building installation, but not to primary supply circuits such as overhead cables. A Fused Lead Set must be used to connect to energised live systems. Refer to the accessories section for options. When selecting 25 cable impedance, an internal 50Hz/60Hz fi lter is automatically switched in. Measuring distance to fault Ensure that the whole length of the cable can be seen on the display, and that the range selected is correct. Find key The Find key searches for the furthest major change of impedance. This may be a fault or the end of the cable if this is a short or open circuit. When found the event is displayed and the cursor placed on the leading edge. The gain, zoom and cursor position may need to be adjusted for accurate measurement. Note that Find does not adjust the TxNull or Velocity Factor. To enable difficult to see faults to be identifi ed, the gain of the instrument can be adjusted. With the gain at minimum small changes of cable impedance may be overlooked. By increasing the gain the fault becomes more obvious. If no faults are obvious, adjust the gain until any major refl ections appear. Open and short circuits should easily be identifi ed. Partial faults can be less obvious. If no signifi cant refl ections can be seen use the “TX Null” to minimise the effect of the output pulse on any potential “near end” faults (refer to section on TX Null). Operation 11 In the event of no refl ections being visible, increase gain until any refl ection can be easily identifi ed. (If no refl ections can be seen, try shorting or earthing the far end of the cable to ensure that you are “seeing” the whole length of the cable). The cursor can also be moved using the LEFT and RIGHT cursor keys. Move the cursor to the beginning of the refl ection. The distance to the fault can then be directly read from the display. NOTE: The distance calculation is performed using the velocity factor set in the TDR. If this velocity factor is not correct for the circuit under test, the displayed distance will be incorrect. Opposite are shown two typical trace displays. The top shows an open circuit at 2000m away; the second a short circuit at 2000m away. 0.67R 3000m2000m 100 0.67R 3000m2000m 100 Operation 12 Instrument Features Menu The Menu key allows the user to change the units of measurement for Distance, Velocity factor, Impedance and Test Rate. By pressing the Menu key the CFL510F will display: To select a function use the GAIN key to scroll up or down the menu. To change the units us the LEFT or RIGHT cursor keys. Available optionsDescriptionOptions Distance UnitThe Units in which the distance tom (metres) or ft(feet). fault is displayed. VF FormatTDR velocity factorRATIO, m/us or ft/us (which should be adjusted to match the cable under test) ImpedanceOutput impedance of the TDR25/50 75/100 Test RateRefresh rate1/second or 3/second Distance Unitm VF FormatRATIO Impedance75 Test rate1s Operation 13 TX Null Without the “TX Null” control, the transmitted pulse would be visible at the beginning of the trace, swamping any refl ections within the pulse length (the dead zone). The TX Null circuit matches the characteristic impedance of the cable under test to produce an equivalent pulse. Subtracting this equivalent pulse from the transmitted pulse effectively removes the dead zone from the display and allows “near end” refl ections to be seen. NOTE:In some cases, it may not be possible to completely null the transmitted pulse. Velocity Factor The velocity factor is used by the instrument to convert the measured time for a pulse to be refl ected, into a distance. It can be displayed as a ratio of the speed of light (eg 0.660 = 66% of the speed of light), or as a distance per microsecond in ft/us or m/us. If the exact length of cable is known and the refl ection from the cable end is visible then an accurate velocity factor can be determined: Locate the refl ection caused by the end of the known length of cable with the instrument set on the shortest possible range to see the end of the cable. Locate the start of this refl ection as described in the Operation section of this manual. Adjust the velocity factor until the correct cable length is shown. Note the VF value for future reference. The measurement of the distance to the fault can now be made with more confi dence. The ability of the instrument to accurately measure the distance to a cable feature relies on the velocity factor being correct. Any errors in the velocity factor are directly related to dista