TDR Fault Detection and Intermittent Fault Detection

TDR Fault Detection and Intermittent Fault Detection

There are several methods that can be used to detect faults and open circuits in metallic cables such as twisted pair, coax and power cables. When a fault occurs more or less continuously, a device known as a Time Domain Reflectometer (TDR) can provide the best means of tracking down the problem. 

When a fault occurs more or less continuously, a device known as a Time Domain Reflectometer (TDR) can provide the best means of tracking down the problem. If the fault is intermittent and not always evident, a TDR with Intermittent Fault Detection (IFD) device would be best. For state-of-the-art IFD fault detection, new technology called Spread Spectrum Time Domain Reflectometry (SSTDR) is now available. Live IFD and SSTDR are examined below.

TDR fault detection

Time domain reflectometry is akin to radar in that the TDR device used for fault detection transmits a signal onto one of the wires of a pair and waits for feedback from the reflected signal on the adjacent wire. When little or no feedback is returned, that is an indication of low impedance and signal absorption at the terminus of the circuit. If there is an open or short of some kind, the signal is returned to the TDR device in a clearly detectable form, with either a positive or negative signal reflection to indicatean increase or decrease in the signal. This, coupled with the magnitude of the returned signal, can be plotted on a graph or expressed in terms of cable length. which helps to pinpoint the spot where trouble is occurring.

IFD devices

Intermittent faults occur fairly often, especially in more complex wiring configurations and can be more difficult to track down since they do not occur continuously. These are commonly attributed to tenuous wiring connections, where two conductors lose and re-establish contact at various times due to environmental conditions. This can easily happen through normal wear, vibration, and/or corrosion, causing occasional failures prior to a total failure.

An intermittent fault will occur as functions of time, duration, and amplitude, which means test equipment must be very sensitive to these characteristics in order to detect them. Any IFD device used must be capable of high test speeds and sensitive to low level impedance, or the intermittence will go undetected. Compared to existing TDR technologies for fault detection, SSTDR Live IFD technology is more sensitive to low impedance signals, which is crucial for sensing the random connection loss which may be attendant in a fault-laden circuit.


Spread Spectrum Time Domain Reflectometry (SSTDR) functions by evaluating spread spectrum signals, and is the newest and most accurate technology available for fault detection. In addition to having the capability of being effective in high noise environments, SSTDR devices can precisely locate the position of any given fault in a circuit, thereby saving enormous time and energy in troubleshooting. 

SSTDR involves sending a signal into the circuit, and comparing the returned signal to a copy of the original. When mathematical algorithms are applied to the shape and timing of the returned signal, the location of the fault can be known with accuracy.

Arc Chaser from T3 Innovation

Arc Chaser from T3 Innovation is an advanced troubleshooting device equipped with SSTDR technology for pinpointing intermittent faults in circuitry. It can detect opens and shorts on either energized or un-energized cables, and easily finds faults which might be triggered by simple vibration occurring randomly. Intermittent events occurring in circuitry is monitored and reported upon, relative to where and when the event occurred. The Arc Chaser is one of the most capable and accurate devices on the market for use in troubleshooting circuit faults, whether continuous or intermittent.