The Ultimate Guide to Sondes

What is a Sonde?

The name “Sonde” derives from the French term for “sounding line”. This perfectly describes how sondes are used in utility location. Sondes are transmitting devices designed to insert into pipelines in order to help with locating and tracing activities.

Sonde transmitters can be used in conjunction with locating equipment to trace underground pipelines, cable conduits and sewers. They are particularly useful for tracing non-conductive pipelines and conduits made of materials such as HDPE, PVC, cement, ceramic, clay, or plastic.

Since non-conductive lines such as these cannot be located with traditional utility locators, this makes the transmitter sonde an important part of any utility location toolkit.

How do sondes work?

Sondes work by emitting an electromagnetic frequency that can be read by a utility locator receiver. The sonde power system is almost always a battery, and most sondes are set to operate at a single industry standard frequency. In the United States, this frequency is 512 Hz. However, some sondes have variable frequency transmission which allows versatility in areas with high electromagnetic frequency interference (EMF).

Sondes can be used in the following locating applications

• Sewer lines
• Water lines
• Storm drains
• Electrical conduits
• Fiber-optic conduits
• Indoor plumbing
• Gas pipelines

How to trace underground pipes using a sonde

To locate pipelines and conduits using a sonde, the transmitter is activated and then inserted into the pipeline. The sonde is then guided or “pushed” along the pipeline. An electromatic receiver, typically from a utility locator system, is then used to trace the pipeline from the ground surface. The operator of the receiver will typically mark the traced line with marking paint or flags as the sonde is traced through the ground.

Utility receivers can vary in features, but many have depth indicators and will alert the user to the location of the sonde with both visual and auditory cues.

How deep will sondes work?

The depth at which a sonde can be read by the operator varies and is dependent on the frequency of the sonde, the output power, the ground conditions, and the signal receiver. Generally speaking, the more powerful the sonde, the deeper it can be read. Loose or wet soils can carry transmission further than compact or dry soils.

Depending on these variables, some transmitter sondes can be traced at depths of over 15 feet (5 m), although depths of 5-10 feet (1.5 to 3 m) are more typical. This is usually adequate for most sewer line or water line tracing activities.

Tools used with locating sondes

Transmitter sondes are not stand-alone instruments. They are designed to be used in conjunction with other locating equipment. The list below contains common equipment used with sondes and how it each is used.

Sonde Receivers

All sondes must be used in conjunction with an electromagnetic receiver. The receiver or “wand” must be able to receive the same frequency that the sonde is emitting. Once the sonde has been inserted into the pipe or conduit to be traced, the receiver is scanned along the ground in the direction of the pipeline’s travel. Audio or visual signals will alert the user to the proximity of the sonde transmitter.

Sondes with sewer cameras

Sewer camera heads can be equipped with a transmitter sonde. These are especially useful for plumbing inspections. Not only will the utility professional be able to view any blockages or breaks within the pipeline, they will also be able to precisely locate the damage location by tracing the camera head with the sonde transmitter attached.

Sondes on Probes, Trace Rods, and Sewer Snakes

Sondes can also be attached to the ends of probes, trace rods, or sewer snakes. These rods are then used to push the transmitter through the pipeline or conduit so that it may be traced with a receiver.

Sondes on Pipeline Pigs or Crawlers

For larger pipelines or industrial pipelines such as those used for gas or oil transport, sondes may be attached to crawlers or pigs. These robotic devices are used to check lines for damage and to confirm that welds and joints are properly made before pressurizing the line. Sondes attached to these machines allow operators to pinpoint the precise location of any potential issues.

Choosing the right sonde transmitter

Most sondes are designed for use in residential and commercial plumbing. This means that specialized units such as those used for industrial pipelines are not necessarily the best tool for the job. Instead, when considering a sonde, most utility professionals only need to consider the following:

Sonde Size: The sonde must be small enough to be fed through the pipeline being traced. If the line has bends or curves, the sonde should be sufficiently smaller in diameter than the pipeline itself to be able to accommodate the bends. Length of the sonde should also be considered if the pipe is expected to have sharp turns or angles.

Sonde Frequency: The frequency of the sonde should match the frequency of the electromagnetic receiver used to trace it. If there is no match, the sonde cannot be traced.

Sonde Power: Most transmitter sondes are battery powered. This can limit the signal output in smaller units. The sonde being used should be powerful enough to allow the signal to be read by the receiver wand.

Sonde Attachment: If the transmitter is to be attached to a probe, trace rod, or sewer snake, the attachment should be secure. This is usually done by a threaded attachment. If the transmitter attachment does not match the attachment of the rod, an adapter may be required.

Transmitter Sondes: A useful locator accessory

Sondes can be valuable tools for plumbers and for utility location professionals. They are not stand-alone devices but scan be useful in locating non-traced or non-conductive pipelines that traditional utility locating equipment cannot locate.

If you are considering purchasing a transmitter sonde, we would be glad to hear from you. Precision Outdoor Tech carries a variety of sondes on our Sondes Collection Page. Please feel free to reach out to us through our contact page and we will be glad to help you find the sonde that best meets your project needs.