How does SSTDR technology work?
SSTDR is evolved from TDR technology and, as its name suggests, SSTDR technology is a combination of traditional TDR and spread spectrum technologies. Originally rooted in secure defence communications technology, spread spectrum is the label used for several technologies where a signal’s strength is maintained, and its bandwidth expanded. This may appear counter-intuitive, as when the signal’s power is spread over a greater number of frequencies, there is no longer a distinct signal peak.
This is where pseudorandom noise signals come in, which are a key element of SSTDR. Pseudorandom noise signals are specific digital signals that are not interfered by and do not interfere with other signals on the line. The signals are so low that they sit within the noise floor of the system. Like TDR, the signals are generated, transmitted along the electrical distribution cables, and reflected by changes in impedance. The SSTDR system correlates the received reflection against the transmitted signal to generate a waveform. The differences between the transmitted signal and the reflection provide an indication of a fault on the line as well as a distance to the fault.
Algorithms are applied to analyse differences in the waveform patterns and automatically identify fault type and provide location information to the operator without the need for interpretation. A spread spectrum of frequencies can be used to complete the test. Higher frequency spreads provide accuracy at shorter distances and lower frequency spreads work best for longer cables.
Combining spread spectrum with TDR represents a significant breakthrough in monitoring and locating real-time changes in live electrical circuits, allowing electrical test and measurement. Here are some resources that provide more information on SSTDR.