By Mike Outmesguine
Certain hand tools are indispensable to the utility worker. A cable stripper, multitool, lineman's scissors and even a hammer occasionally make the job easier, safer and faster.
Electronic test equipment is indispensable, too. Yet as formerly bulky, hard to use electronics evolve, the options to expand the list of "indispensables" is growing. As an example of this trend, it wasn't long ago touch screen tablets were high cost, fragile items more at home in an office than outdoors. Touch screen tablets are now small, light, sturdy and fast becoming indispensable on the job site.
Going beyond the multimeter, the time domain reflectometer (TDR), a formerly bulky, difficult-to-use, electronic cable fault tester that was better suited in a workshop than on a truck, has turned into a hand-held, automated tool that is indispensable to those using it in the field. Cable troubleshooting jobs that would take several hours using a multimeter and cable tone generator can be cut to a fraction of that time with the automated features in a newer field-ready TDR.
A TDR is used to test for cable length, faults, junctions and other impedance changes on a cable run. Often compared to radar, TDR devices send a pulse down the cable while checking for reflections. Those reflections tell a story. If a reflection is received 50 nanoseconds after the transmit pulse, for example, the TDR will observe the time delay and convert that into distance displayed in feet or meters.
Spread Spectrum Time Domain Reflectometry
Typical TDR testers require a cable under test be disconnected on both ends for a proper test because of signal interference or to avoid damage to the tester itself. T3 Innovation, a provider of cable testing solutions, provides many TDR models that include spread spectrum time domain reflectometry (SSTDR)-a technology that allows the signal pulses and reflections to be observed on live cables. Spread spectrum signaling prevents interference caused by operating equipment such as telephone, networking traffic and power lines. The T3 Arc Chaser and Power Prowler can monitor live wires up to 600 Volts. And, testing with SSTDR requires no downtime. Testing cables while an office is in operation is possible.
Three examples of in-field TDRs are the Power Prowler, Cable Prowler and Arc Chaser by T3 Innovations. Each model is encased in a hand-held unit with a full-color, high-resolution LCD screen but differ in features and use cases.
The Power Prowler combines an easy-to-use digital multimeter (DMM) with an equally easy-to-use spread spectrum TDR. The TDR function discovers cable length and automatically checks for shorts and opens. It can also monitor a line for circuit changes such as turning on and off a switch or finding a loose wire. The auto-range DMM function measures ac and dc volts, ohms and continuity.
Switching between the TDR and DMM functions occurs with the press of a button. Keep the leads attached to the target circuit and select one of three icons on the screen: Multimeter, Fault Location and Live Event Detection.
Using the Cable Prowler to discover a cable configuration is straightforward. For network discovery, the Cable Prowler has both an active online and passive offline mode. For coax and telephone discovery, the Cable Prowler works offline-the cable is disconnected from the active system. This low-cost TDR does not yet feature the spread spectrum TDR technology to work on live cables.
In network online/active discovery, the Cable Prowler will auto-negotiate an active link to the attached network device (e.g. a central network switch.) An LED link light is on the face of the unit. It will also test for Power over Ethernet (PoE) capability supported by the link. The LCD display will show negotiated speed and link capability.
The Arc Chaser, an SSTDR with a color LCD touch screen, performs on-demand cable fault location and length measurement in addition to an automatic live intermittent fault detection, which will continuously monitor a line for faults such as opens, shorts or connector problems. The live intermittent fault detection can monitor a line up to 24 hours at a time (or 1,000 events). This feature can help technicians find intermittent problems while the line is under normal use. For complaints of brown-outs, attach the unit to the line and download the results for later analysis.
The Arc Chaser will display graphical charts of the cable being measured or a simple text display of its automated findings. Experienced technicians will view the graph and come to understand the measured line condition. It is also capable of savings the results to a removable SD Card for transfer to a computer for off-device record keeping and cabling analysis. Reports can be saved as a PDF summary of test results or as a more detailed CSV file format for viewing in a spreadsheet or import into a database.
The TDR hand-held test tool has moved out of the lab and into the field. Once a TDR tester is onsite, helping workers on a cable troubleshooting job, its benefits are immediately realized.
About the author: Mike Outmesguine is a technologist and writer. His recent projects include founding science, technology, engineering, art and mathematics (STEAM) Makerspaces and fostering small business startups. He is a wireless communications expert and has tested cables while working with data networks, wireless devices and antenna systems in the utility, commercial and defense industries.