TDR vs Acoustic Pinpointer: Which Cable Fault Location Method Do You Need?
A common question from contractors and utility teams shopping for cable fault location equipment: "Should I buy a TDR or an acoustic pinpointer?"
The honest answer: they are not alternatives. They are two sequential steps of the same fault location workflow. Buying one without the other is like buying a GPS but no map — you'll get part of the way and then stop.
This article explains exactly what each tool does, when you need each one, and why professional fault location teams always use both.
What a TDR Does (and What It Can't Do)
A Time Domain Reflectometer (TDR) sends an electrical pulse down a cable and measures the time until the reflected signal returns. Since the propagation speed of the cable is known, the distance to a fault can be calculated.
What a TDR is excellent at:
- Telling you the distance to a fault (e.g., "780 meters from this end")
- Working on long cables (up to 100 km with professional units)
- Detecting low-resistance faults and open circuits
- Measuring cable length
What a TDR cannot do:
- Tell you exactly where on the ground to dig
- Detect high-resistance faults without conditioning
- Work on live cables (standard models)
The output of a TDR is a distance reading, not a physical location. That distance could be 780 meters along a cable that curves, crosses roads, and dips under buildings. Someone still has to walk that distance and figure out where "780 meters" is on the ground.
What an Acoustic Pinpointer Does
An acoustic-magnetic pinpointer detects the fault's discharge when it is stressed by an impulse generator. It picks up:
- The acoustic "thump" — the sound of the fault discharging
- The magnetic pulse — the electromagnetic field that travels to the fault
Where these two signals converge on the surface is the exact fault location.
What a pinpointer is excellent at:
- Telling you the exact spot to dig (within half a meter)
- Confirming the fault location on the ground
- Working alongside an impulse generator (thumper)
What a pinpointer cannot do:
- Measure distance — it needs a TDR to know roughly where to search first
- Work on low-energy faults that don't produce a strong discharge
The Workflow: Why You Need Both
Skipping step 1 means walking along the whole cable with a pinpointer, listening for thumps — slow and impractical on long cables. Skipping step 3 means digging at meter 780 and hoping the cable lies straight — a gamble that wastes hours.
Integrated Systems Do Both
Rather than buying separate units, many teams choose an integrated system that includes TDR, impulse generator, and pinpointer together:
- Portable systems bundle all three in transportable cases — ideal for contractors who service multiple sites
- Trolley-mounted systems (like the A50/A52) integrate everything into one mobile rig
- Vehicle-mounted systems (like the A40) put the complete toolkit in a service van for rapid network-wide response
TriEdge Technologies offers complete fault location systems at factory-direct prices — 40–60% below equivalent Megger or BAUR setups.
FAQ
Do I need both a TDR and a pinpointer? Yes, for professional fault location. The TDR narrows the search distance; the pinpointer finds the exact excavation point. They work together, not as alternatives.
Can I locate a fault with just a pinpointer? On short cables, technically yes — you walk the cable and listen for the discharge. On any cable over a few hundred meters, this is impractically slow. A TDR pre-location step first is the professional approach.
Why can't my TDR see the fault? If the fault has high resistance, the TDR pulse passes it without reflecting. The fault must first be conditioned with a high-voltage supply, then re-tested.
What's the accuracy difference? A professional TDR gives distance accuracy of ±0.5 m. A pinpointer gives surface accuracy of under 0.5 m. Together they reduce total repair time from days to hours.