Biddle BTDR1500_UG 电路图.pdf

IEC/EN 61010-1 C O M P L I E S W I T H M BTDR1500 Bridge Time Domain Reflectometer IEC/EN 61010-1 C O M P L I E S W I T H User Guide* Manuel Utilisateur Bedienungsanleitung Gua del usuario Guida per lutente Gebruikersgids *Also available in Swedish, Norwegian, Finnish, Danish. Please quote: 6172-620 RadioFans.CN 收音机爱 好者资料库 2.0 Introduction5 3.0 User Controls and Display6 4.0 Operation7 5.0 Meter7 6.0 TDR7 7.0 Instructions for Bridge 11 8.0 General Specification18 9.0 Repair and Warranty20 2 Contents Contenus 22 Inhaltsverseichnis 43 Contenido 66 Indice 88 Inhold 100 RadioFans.CN 收音机爱 好者资料库 Symbols used on the instrument Caution: Refer to accompanying notes Equipment protected throughout by Double or reinforced Insulation Instrument flash tested to 3.7 kV r.m.s. for 1 min. Equipment complies with current EU Directives 3 3.7 RadioFans.CN 收音机爱 好者资料库 SAFETY WARNINGS This instrument primary use is for testing telecomm cables and so it meets the safety requirements of IEC 60950 third Edition (1999-04). It also meets the safety requirements of IEC 61010 parts 1 and 2 but without a category of installation as the instrument must not be directly connected to an energised Mains Supply. The instrument is designed for used on de-energised circuits, however, when used with telecomm cables, it may, in normal use, be subject to telecomm network voltages up to TNV-3 as defined by IEC-60950. Do not exceed the limits of this tester. If it is to be used in situations where hazardous live voltages may be encountered then an additional blocking filter must be used to isolate the instrument. CAUTION (Risk of electric shock) 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. Never connect the instrument to circuits that may be hazardous live. 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. 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. NOTE THE INSTRUMENTS MUST ONLY BE USED BY SUITABLY TRAINED AND COMPETENT PERSONS. 4 Thank you for purchasing this quality Megger product. 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 Megger BTDR1500 is an advanced instrument capable of identifying a wide range of cable faults. It incorporates an Insulation Tester, a DC Voltmeter, Time Domain Reflectometer (TDR) and a Digital Bridge to allow for the accurate location of short and open faults on a cable. The Voltmeter measures a DC voltage to 250 V and can verify if a telecomm cable has a Telecomm Network Voltage (TNV) present on it. The TDR has a range of 10 m to 3000 m. It transmits a narrow pulse of electrical energy along a pair of conductors within a cable and times how long any reflections of the pulse take to get back. By knowing how fast these pulses travel through a given cable, the measured time can be converted to a distance to fault. The reflections are caused by impedance changes within the cable that are significantly different from the characteristic impedance of the cable. A partial to full short circuit will have a negative going reflection whereas a partial to full open circuit will have a positive going pulse. If the change in impedance is less significant, the ability to discern the cable feature accurately using the TDR technique alone can be difficult and so the Megger BTDR1500 provides a Digital Bridge for this occasion. The Digital Bridge can measure the insulation resistance up to 200 M (insulation test), the loop resistance up to 2 k (2-wire loop test) and the series leg resistance of up to 1 k (3-wire loop test). Where a fault causes the insulation resistances to lie below 20 M, the fault position can be determined (AUTO test) relative to the meter end and also relative to the far end where a loop has been made by fitting a strap between the wire under test and one or two return wires. In the case of a single return wire (2-wire test method), the position of the strap is assumed to be at the position of half the total loop resistance. If two return wires can be used (3-wire test method) the position of the strap will be known to greater accuracy and will be independent of the resistance of either of the return wires. 5 2.0 INTRODUCTION 3.0 USER CONTROLS AND DISPLAY: The controls of the BTDR15000 have been arranged such that the instrument is easy to use and easy to learn how to use. The precise function of each control depends on the current mode selected and is detailed as follows: Figure 1 The BTDR Controls # NameMain MenuVoltmeterBridgeTDR 1Display-128 x 64 pixelShows current settings or measurement results relevant to the selected mode. 2TX Null - Rotating dial-Analogue control to minimise O/P pulse. 3Cursor Left - -Reduce selected valueMoves cursor left/reduces Uni-directional push buttonselected value 4Menu - Bi-directional Moves menu cursor Selects E to A or EMenu left/right ctrl andClockwise/anti-clockwise push buttonleft or rightto B V and can select EXIToption selectoroption selector. 5Cursor Right - -Increase selected valueMoves cursor right/increases Uni-directional push buttonselected value 6Power On/OffTurns the instrument On/OFF 7Gain - Bi-directional Proceeds with selected Proceed with Proceeds with selected Increases/decreases gain push button Menu optionEXIT selectionMenu optionsetting, confirm EXIT. 8BacklightTurns the instrument backlight On/Off 9ContrastAnalogue control to correct the display contrast for extremes of temperature 10 O/P SocketsLabelled E, A, B any errors in the velocity factor are directly proportional to distance measurement errors. Please refer to the Quick Reference Guide for a table of typical Velocity Factors. 6.4 PULSE WIDTHS The BTDR1500 pulse widths range from 8 ns to 3 s to overcome signal attenuation and enable the instrument to see further down a length of cable. In distance terms for the size of the transmitted pulse, this represents a transmitted pulse from as small as 1.5m to 600m! (This assumes a velocity factor of 0.67.) Without TX Null, this would be an enormous dead zone, but with the instrument correctly balanced, faults can be seen well within the pulse width. As the measured distance is taken at the start of the reflected pulse, the size of the pulse width does not affect the accuracy of the measurement. However, if the first feature does not give a complete reflection such that the instrument can see beyond it to a second feature, the ability to discern between features is affected by the pulse widths. If there are multiple features, the instrument can only fully discern between them if the features are more than the pulse width apart. Hence, for discerning multiple features, the instrument should be used with the shortest range, and so smallest pulse width, that can see both features (refer to the pulse width table in the specification). 6.5 TECHNIQUES FOR TDR USE To improve on the accuracy of the measurement and the ability to discern faults, numerous techniques can be used, depending on the situation encountered. Here are a few for your information: 6.5.1 Test the cable from both ends When fault finding a cable it is good practice to shoot the cable from both ends. Particularly in the case of open circuit faults, the true end of the cable is not visible. Thus, it is harder to estimate whether the answer that is obtained is realistic. If the measurement is made from both ends, then the combined answer should add up to the expected length of the cable. Even in the case when the true end of the cable is still visible, the reflections after the fault may be too obscure to analyse clearly. In this case, measurement from both ends yields a clearer picture as well as improved accuracy. It is also good practice to follow the cable route with a cable tracer, as not all cable runs will be straight. It can save a great deal of time if the exact route of the cable is known as faults will usually be found at points were human intervention has occurred, junction boxes splices etc. 6.5.2 Reflections caused by Mismatches On very short faults, when there is a mismatch between the test lead impedance and the cable under test a proportion of the reflected wave from cable fault bounces off this impedance mismatch. This reflection generates an apparent second fault at double the first faults distance. If there is sufficient energy left in the wave a third and fourth reflection can occur. The problem is more evident on 50 and 25 cables (i.e. power distribution cables) as the impedance mismatch is greater and the signal attenuation is less. This will show on the screen as multiple, equidistant faults of diminishing amplitude. 9 6.5.3 Bridge Taps Bridge taps occur when another pair of conductors is connected to a pair in the main cable to form a branch or party line. At the branch or bridge junction, a short circuit type fault will occur due to the characteristic impedance halving at that point. If a pair of conductors has a large number of taps, then the waveform displayed will be difficult to evaluate if specific knowledge of the cable network is lacking. 6.5.4 Load Coils Load coils are used on telephone lines to increase the line inductance, so improving the transmission characteristics of long lines. The inductive load coils appear as open circuits to a cable fault locator. To test beyond the coils, a new test site further upstream has to be chosen. 6.6 TDR APPLICATION NOTES The BTDR is intended for use on de-energised circuits only. For operator safety the instrument is double insulated, it also incorporates safety terminals. For complete list of the Safety Standards adhered to, please refer to the specification (8.1). Please refer to the enclosed Quick Reference Guide for a list of typical waveforms relating to various cable features. 6.6.1 Metallic Shorts These are caused by metallic contact between two conductors of a cable pair. This produces a strong downward pulse. See the Application Card supplied with the BTDR. 6.6.2 Sheath Shorts These are caused by a conductor in a cable making metallic contact with the metallic sheath of the cable. To locate a sheath short, disconnect the sheath from earth and then connect one terminal to the sheath. Connect the other terminal to each conductor in turn until you locate the shorting conductor. 6.6.3 Crossed Conductors When multiple twisted pair circuits pass through the same junction box, there is a possibility crossing conductors from adjacent pairs. This produces waveforms similar to metallic shorts but with reduced amplitude. Acrossed conductor can be located from either adjacent pair but is more pronounced if the BTDR is connected across both crossed conductors. 6.6.4 Metallic Open Circuits This is caused when one or both conductors of a pair are disconnected or broken and produces a strong upward fault pulse. 6.6.5 Resistive joints or Splices These are caused by poor joints or the joining of two cables at a junction box. They produce upward going fault pulses whose amplitude depends on the quality of the joint. 6.6.8 Water Ingress Faults When a cables sheath is damaged, water can soak into the cable and contaminate the insulation medium. The affect this contamination has is to cause a drop in cable impedance at the start of the water ingress (downward pulse) and a corresponding increase in cable impedance at the end of the ingress (upward pulse). If the contamination is gradual then the impedance change is also gradual and so the pulses shape more extended and rounded. If the whole cable is contaminated then the fault can be difficult to locate, as there is no impedance change. 10 6.7 TDR SPECIFICATION Except where otherwise stated, this specification applies at an ambient temperature of 20C. General Ranges:10m, 30m, 100m, 300m, 1000m, 3000m and Auto (30ft, 100ft, 300ft, 1000ft, 3000ft, 10000ft) Accuracy:1% of range pixel at 0.67VF Note- The measurement accuracy is for the indicated cursor position only and is conditional on the velocity factor being correct. Resolution:1% of range Output pulse:5 volts peak to peak into open circuit. Pulse widths determined by range Range10m30m100m300m1000m3000m Pulse width8ns30ns100ns300ns1000ns3000ns Gain:Set for each range with four user selectable steps. Velocity Factor:Variable from 0.30 to 0.99 in steps of 0.01 Output impedance:100 TX Null:An internal circuit can simulate a line with impedance in the range 0 to120 to enable the displayed transmitted pulse to be nullified. Update Rate: Once a second for 5 minutes after last key-press. 7.0 INSTRUCTIONS FOR BRIDGE USE When the bridge is selected from the Main Menu, the Bridge Menu is displayed as follows: Figure 6 - The Bridge Menu The Bridge Menu has four options: AUTO / INSULATION / LOOP / EXIT. Use the Menu key (#4, table 1) to highlight the required selection and then the Up / Down Gain key (#7, table 1) to proceed with the selection. The right facing triangle next to select indicates that another menu option (the EXIT option) is off-screen to the right and requires pressing right when LOOP is highlighted. At this point, INSULATION / LOOP / EXIT will be the visible menus with a left facing triangle next to Press MENU indicating that another menu is now available to the left. 11 AUTOI NSULATI ONLOOP Pr ess M ENU t osel ec t Pr esst o p r oce ed BRIDGE M ENU 7.1 CONNECTIVITY When you use the BTDR in bridge mode all four of the terminals can be used; the exact configuration required depends on the test in progress according to the following diagrams: The 2-wire test method assumes that the Good Line and the Faulty Line are of the same gauge wire and approximately equal in length. Then the assumption that the strap is at half the total loop distance is valid. However, it is preferable to use a second return wire if possible to make use of the 3- wire testing method. Each of the Good Lines can be of different resistances and lengths compared with the Faulty Line. This can allow for a direct measurement of the resistance (and hence distance) to the strap without making any assumptions and so can give a more accurate fault position. 7.2 Auto Test The Auto Test automatically runs through a series of tes