Advanced Systems Tester 900AST Series Coaxial Wire Testing Technical Tip December 2005 78-8135-6156-6-A
3M™ Advanced Systems Tester 900AST Series Setup for Use Battery Requirement The battery holder holds six “AA” standard alkaline batteries and should be installed prior to using the unit. Please see the 900AST tester manual or DVD for battery installation instructions. Always initiate a self-calibration after installing new batteries. The battery symbol in the upper right-hand corner of the display gives an indication of the approximate battery capacity. Each bar represents one-quarter of the full capacity.
M™ Advanced Systems Tester 900AST Series Keypad The 900AST tester keypad has twelve yellow and red “Control Keys” and nine blue “Function Keys”. Additional blue keys on the keypad are reserved for future expansion and have no designation or current function. Control Keys Use the red and yellow keys to control and setup the 900AST tester and its functions. Use the [Return] key to return to a previous step in a function. Use the [Contrast] key to adjust the contrast or to turn the backlight on or off.
3M™ Advanced Systems Tester 900AST Series Contrast and Backlighting Note: Use of backlight decreases available battery capacity. Press the key to display the contrast screen. Use the and keys to adjust the contrast. Press key again to turn the backlight on or off. the Use the key to return to previous screen. Function Keys Use the blue keys to select the different tests in the 900AST tester. The blue keys become number or letter keys when editing. Use the [Voltage] key to measure DC or AC voltage.
3M™ Advanced Systems Tester 900AST Series Use the [RFL] key to find the distance to a resistance fault between two conductors or a conductor and ground. This key is used for editing only. Use the [TDR] key to activate the Time Domain Reflectometer. Use the [Auto] key to activate automatic TDR trace analysis. CAUTION The 900AST tester is a tool for troubleshooting wiring problems. It is not designed for troubleshooting electronic circuits or instrumentation.
3M™ Advanced Systems Tester 900AST Series TDR Setup The TDR features a setup function that allows you to select the type of Coaxial wire to be tested. From the TDR Menu, press the enter the TDR Setup. Setup key to Press the select key and the and arrow keys to highlight coaxial cable for wire type. select key to move to the wire gauge Use the and keys to highlight the type box. Use the of coaxial cable to be tested and select ‘minimum possible’ or ‘last used’ initial measurement length setting.
3M™ Advanced Systems Tester 900AST Series TDR Test Modes Press the mode. or keys to move to the desired Press the key to accept the highlighted mode and start the measurement. Single Trace Use the TDR Single Trace mode to test a single coaxial wire or circuit.
3M™ Advanced Systems Tester 900AST Series Dual Trace Dual Trace is used to compare two coaxial circuits at the same time (usually a faulted and a good circuit). Connect the TDR test leads to the (Red and Black jacks) and connect the second TDR test lead set (Blue and Yellow jacks) to the reference circuit. This mode is valuable when testing a system with multiple coaxial wires serving the same system. Memory Memory mode is used to compare a circuit under test to a stored trace in memory.
3M™ Advanced Systems Tester 900AST Series Use the and keys to highlight the desired key to display the stored stored result. Press the trace on the bottom of the TDR screen and the “live” trace on the top. You may move the cursor by and keys. using the The control settings for the stored trace can be viewed by pressing the or keys but the settings cannot be changed. The TDR Memory function includes a Difference (‘Diff’) control, accessible from the memory screen by pressing the key.
3M™ Advanced Systems Tester 900AST Series Length allows you to set the distance (or span) from the left side of the screen to the right side. The left side of the screen is at the end of the BNC test lead and the right side is the farthest distance that can be displayed with the selected length Use the or keys to move forward or backward through the TDR controls. Use the and keys to change the parameters for the control selected. Available controls are Length, Filter, VP, Pulse, and Gain.
3M™ Advanced Systems Tester 900AST Series Press the key. The 900AST tester will display the Save Results screen as follows: Use the blue keys to enter an alphanumeric ID. The ID may have up to twelve digits. Whether a number or letter is entered depends on how many times the key is pressed. As an example, if the Ohms key is pressed once, the number “3” will be displayed. If the same key is pressed twice, the letter “d” will be displayed.
3M™ Advanced Systems Tester 900AST Series generally cause small upward peaks due to a change in impedance. To determine if an upward event is an impedance change or a main event fault you may go to the other end of the coaxial cable and disconnect it. Next, take a jumper and short the inner conductor to the outer shield. If you see a large downward deflection in the trace the small peak is impedance change. Conversely, if you can’t see the short or downward deflection you have an open circuit in the cable.
3M™ Advanced Systems Tester 900AST Series Short Circuit A short circuit (or zero-Ohm resistance fault) will show up as the lowest dip on the screen. You cannot see events past a short circuit Branch Circuit The beginning of the branch circuit will look like a small dip and the end of the branch will look like an open (upward peak). Use the 900AST tester Resistance function to measure the resistance of the conductors. If the resistance is high, you may suspect a branch circuit.
3M™ Advanced Systems Tester 900AST Series Connect the 900AST test leads to the coaxial conductor under test. Press the key to access the Soak test from the Resistance screen. Use the key to save the active resistance to the “Snap Shot” area. Rising resistance in the active box typically indicates moisture while falling resistance indicates corrosion. Auto TDR for Coaxial Fault Detection Use the Auto TDR function to have the 900AST tester analyze and interpret a TDR coaxial cable trace.
3M™ Advanced Systems Tester 900AST Series To change the coaxial configuration go to the TDR function and press the Setup key. Use the and keys and the Blue numeric keys to enter the length of cable to analyze. Enter a length longer than the cable being tested but as close as possible to the total length of the cable. When the correct information is displayed on the Auto TDR screen, press the key to start the analysis.
3M™ Advanced Systems Tester 900AST Series In this case the low impedance anomaly at 24 inches is detected but not classified. The Auto TDR displays ‘????’ below the trace. Restoring the Aircraft After Testing/ Troubleshooting Disconnect the 900AST TDR test cable from the aircraft wiring. Also, remove any adapters (if used). Ensure the other end of the coaxial cable is reconnected.
3M™ Advanced Systems Tester 900AST Series This is the EU symbol for equipment that is covered under the Waste from Electrical and Electronic Equipment (WEEE) directive per CENELEC Specification 5041. It indicates that certain products should not be discarded in the trash, but rather should be recycled. This applies to all electronic pluggable and battery powered products. 3M is a trademark of 3M Company.
