Using Accessories, Part 2: Sondes

Follow Avatar Anthony Caplin
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Sonde overview

A sonde is a self-contained battery operated transmitter used for tracing the paths of pipes, ducts, sewers and drains and in the precise location of blockages or collapses. The sonde can be fitted to a flexible rod for insertion or pushing through pipes etc. and the smaller diameter sondes can be used in conjunction with jetting machines and blown through the duct. A suitable Radiodetection locator can then be used to locate the sonde.

Choosing a suitable sonde

Radiodetection offers a wide range of sonde to suit most applications: From the ¼” / 6mm diameter S6 33kHz microsonde which, with a range of 6.6” / 2m, targets fiber-optic micro ducting or other small non-conductive pipes, to the 33kHz Super Sonde, which with a depth range of 50 feet / 15m targets deep sewer pipes.

Check that the sonde has sufficient range for the application and is dimensionally small enough and sufficiently robust for the application. Ensure that the frequency of the sonde corresponds with the locator frequency; the locator will not locate the sonde unless the frequencies are the same. Sondes are marked with their transmitting frequency. Ensure that the means of propelling the sonde is available together with the correct fittings and couplings.


Insert a new battery into the sonde. A new battery or a freshly recharged battery should be used at the beginning of each day and preferably at the start of each new job.

Before inserting the sonde, check that the sonde and locator are at the same frequency and working correctly. To do this, place the sonde on the ground at a distance from the locator that is equal to the rated depth of the sonde. Point the locator at the sonde with the antenna in line with the sonde (the opposite of using the locator to locate a line) and check that the bargraph reading exceeds 50% at maximum sensitivity.

Propelling a sonde

Sondes have a thread at one end for connecting to drain rods, or to other devices for inserting and propelling the sonde along a drain or duct. Sondes may be floated along drains at the end of a tether and floats are available for fitting to the sewer sonde and super sonde. Sondes can be strapped to high-pressure water jets or similar devices used for cleaning, maintaining and inspecting drains. Sondes used in underground drilling and boring operations are normally housed in the boring or drill head behind the boring or drill bit.

Locating and tracing a sonde

Insert the sonde in the drain or duct access and locate it while it is still just in view at the drain or duct entrance. Hold the locator vertical directly over the sonde with the antenna in line with the sonde. Adjust the locator sensitivity so the bar graph reads between 60% and 80%.

The sonde radiates a Peak field from the center of its axis with a ghost signal at each end of the Peak. Move the locator a little way behind and then in front of the axis of the sonde to detect the ghost signals. Finding the two ghost signals positively confirms the locate. Reduce the locator sensitivity to lose the ghost signals but still indicate a clear Peak response directly over the sonde. Locator sensitivity is now set for tracing the duct or drain unless the distance between sonde and locator changes.

Propel the sonde three paces along the drain or duct and stop. Place the locator over the supposed position of the sonde. Do not adjust the sensitivity level.

Sonde deployment


To locate a sonde:

  1. Move the locator backwards and forwards and stop when the bar graph indicates a Peak. You can use the LCD compass to orient the blade of the locator with the direction of the sonde.
  2. Rotate the locator as if the blade is a pivot. Stop when the bar graph indicates a Peak.
  3. Move the locator from side to side until the bar graph indicates a Peak.
  4. Repeat 1, 2 and 3 with the antenna vertical and resting on or just above the ground. The locator should then be directly above the sonde with the antenna in line with it. Mark the position of the sonde and its direction.
  5. Propel the sonde a further 1 or 2 meters, pinpoint, and mark the position. Repeat this pinpoint procedure at similar intervals along the line of the drain or duct until the survey is completed.
Locating a sonde

Checking sonde depth

The RD8100 locator will automatically display the depth of a located sonde providing the locator is correctly oriented and positioned above the sonde. Using the LCD compass as a guide, rotate the locator until the compass indicates the sonde is in East / West position.

Calculating sonde depth

Calculation method

Pinpoint the sonde. Move the locator in front of the sonde and still with the antenna in line with it, increase sensitivity to find the Peak of the ghost signal. Move the locator to behind the sonde ensuring that the locator blade is always in line with the sonde. Find the null positions A and B (as illustrated above). Measure the distance between them and multiply by 0.7 to give an approximate depth measurement.


The Flexitrace is a traceable plastic covered fiberglass rod incorporating wire conductors and is used for locating small diameter, non-metallic pipes to a depth of 3 meters. The Flexitrace can be inserted into a pipe or duct as small as 9mm / 3/8” internal diameter, and with a minimum bend radius of 250mm. Batteries are not required, as the FlexiTrace is powered by any Radiodetection transmitter.

The FlexiTrace has a maximum power rating of 1W. When using the FlexiTrace with a Radiodetection Tx-5 or Tx-10 transmitter the output limit must be set to 1W in the MAX P menu and the output voltage limit set to LOW in the MAX V menu.

No settings are required for the Tx-1 transmitter.

WARNING: Failure to follow the Tx-5 or Tx-10 instructions above may result in the tip of the FlexiTrace becoming too hot to touch, resulting in risk of personal injury and damage to the equipment.

The FlexiTrace can be used in two modes: Sonde mode or Line mode. In sonde mode only the tip of the FlexiTrace is energized whilst in line mode its whole length is energized.

To use as a sonde, connect both transmitter leads to the FlexiTrace stud terminals. As the FlexiTrace terminals are not colour coded it does not matter to which terminals the leads are connected. To use the FlexiTrace in line mode, connect the red transmitter lead to one of the FlexiTrace terminals and connect the black transmitter lead to a suitable ground connection.


For further Information click on the links below:

Sondes & flexi trace

Sondes Userguide

Flexi rod and flexi trace information sheet