Pipe location systems use a variety of technologies to detect underground utilities.

The objective always is to make locating as easy as possible for technicians while also ensuring high accuracy.

The TraceMaster II system from Schonstedt Instrument Co. can be used in any of three modes to allow operators to map sewer and water pipes and other buried infrastructure. When it is possible to send a probe into the target line, the system is used with a sonde that sends a 512 Hz signal to the handheld receiver. The sonde is typically used in sewer lines of any composition, including clay, concrete or plastic.

In locating water lines, the system can be used in the conductive or inductive mode. Both modes require the pipe being located to be metal. In the conductive method, a transmitter is clipped to an above-ground metal object, such as a fire hydrant, and to a ground stake perpendicular to the water line direction. The transmitter sends a signal through the line, which the receiver picks up.

If a metallic connection to the line being located is not accessible, the operator can use the inductive method, sending a signal from the transmitter into the ground and determining the pipe’s location by the way the signal bounces back to the receiver.

Racine (Wis.) Wastewater Utility employees received a demonstration of the TraceMaster II on Jan. 21, 2008, at the utility’s offices at 2310 Center St. Demonstrators were James Bach, national sales manager, and Scott Rauen, regional sales manager, for Schonstedt. Utility employees Keith Messerschmidt and Owen van Swol took part.

Walk-around

The principal components of the TraceMaster II are the receiver and transmitter. The yellow-and-black handheld receiver is about 30 inches long and weighs less than 4 pounds. It has an LCD digital readout and control panel at the top and a sensor assembly at the base.

The operator holds the receiver like a cane, but keeps it slightly above the ground, the sensor assembly pointing down and the LCD/control panel held horizontally. The screen indicates the strength of the signal, and arrows show the target’s location relative to the receiver. It can also display a calculation for the depth of the utility detected.

The device includes four controls: two one-handed knobs and two membrane buttons. At the left of the control array is a knob that controls the strength of the signal (or gain) coming to the receiver. To its right is a button to change the transmitter frequency when the unit is in the conductive or inductive mode. To the right of that is a second button, which when pushed displays the calculated depth of the target.

On the far right of the panel is the second knob, which controls the volume of the sound that indicates the proximity of the target. Icons displaying the battery charge level in the receiver and the transmitter also appear on the screen.

The transmitter includes a radio link antenna that allows it to communicate with the receiver so that the operator can change the frequency that the transmitter emits using a control on the receiver. The transmitter is contained in a high-impact yellow plastic case IP65 under an international standard, signifying that it is dustproof and waterproof. The case can store the sonde and the conductive clips and ground stake for using the device in the conductive mode.

The TM 50910 sonde, an accessory available with the TraceMaster II unit, emits a standard 512 Hz signal. The transmitter uses eight D batteries, and the receiver eight AA batteries.

Operation

Bach, Rauen, Messerschmidt and van Swol met on a cold morning outside the Wastewater Utility offices under an overcast sky with light snow. While the weather was not ideal, Bach said that the near-zero temperatures would not interfere with the locator.

For the first demonstration, Bach used duct tape to attach the sonde to a pushrod sewer camera supplied by the utility. Typically the sonde would be attached to a sewer rod, but the Racine crew could not use their rod because it is shielded by a plastic tube that the sonde could not pass through.

Messerschmidt and van Swol lowered the camera cable, sonde attached, into the sewer and guided it into the pipe. As they pushed the sonde in farther, Bach walked with the TraceMaster II receiver down the middle of the street, slowly moving the unit from side to side. The receiver emitted a high-pitched beeping, an electronic peak sound to signify when it was closest to the sonde. Bach adjusted the gain rheostat to diminish or boost receiver sensitivity.

Walking about 15 feet, Bach showed how the unit could be used from the street to map the path of the sewer pipe. As he adjusted the gain, the LCD displayed the strength of the signal from the sonde as a percentage. At any given point, the percentage shifted as Bach moved the receiver laterally. The peak percentage number in any lateral pass indicated the precise location of the sonde in the pipe.

A crew on assignment in the field would likely mark the path with spray paint to give road crews planning a street repair guidance about the pipe’s location.

After observing Bach, Messer-schmidt took the receiver and repeated his actions, following the trail of the pipe as the receiver picked up the sonde signal.

Bach and Rauen then demonstrated the device in the conductive mode on a nearby water line. They used conduction clamps to attach the transmitter to a fire hydrant, then shoved a metal grounding rod into the nearly soil and attached it with a cable to the transmitter.

When turned on, the transmitter sent a signal through the metal hydrant and into the metal water line. Walking with the receiver away from the hydrant, Bach determined the path of the line. In this mode, Bach demonstrated how the LCD readout displayed the location and depth of the target line.

As Bach slowly waved the receiver back and forth in increments of about 6 inches to 1 foot, the unit emitted an electronic tone. As with the sonde method, the unit gave a reading for the signal received in terms of percentage, which could be adjusted using the gain control.

In addition to observing when the signal percentage peaked, the screen displayed an arrow pointing right or left, indicating in which direction the operator should move to directly locate the water line. When both arrows became visible at once, pointing at each other, a vertical line appeared between them, and the tone turned into a rapid beeping, indicating that the water line was directly beneath the unit.

Bach also pressed the depth button, which activated a display on the LCD screen showing the depth of the line — 5 feet, 9 inches at the point detected. Using a thumb to press the frequency button on the receiver control panel, Bach changed the frequency of the signal sent by the transmitter.

He concluded by briefly demon-strating and describing the inductive method of location, which is used in more remote situations where there is no external connection to the line being located.

The transmitter is placed above a known starting point for the line. That location might be derived from a plan or other documentation. The transmitter broadcasts a signal into the ground, where it is picked up by and travels along the metallic pipe. The receiver picks up the signal. Bach explained that the inductive method is less precise because variations in the ground conditions can distort the signal. However, it offers information not otherwise available if an area is not mapped.

Observer suggestions

Messerschmidt reported that the TraceMaster II was light and easy to carry. He noted that using a locator increases confidence. With-out a detector, he said, finding an underground pipe is more labor intensive and involves more guesswork. Maps may or may not be up to date or accurate.

With a detector, “When you’re within five feet of what you’re looking for, you’re not digging all over the place,” he said. He found the device itself simple to use. With very few controls, it appeared easy to learn to operate. The sound emitted, although annoying, was clear and easy to interpret. The digital readouts on the LCD display were clear and intuitive.

Manufacturer comments

The unit offers a choice of four frequencies: 575 Hz, 8 kHz, 82 kHz, and 455 kHz. The lowest frequencies are for detecting smaller pipes, and the higher frequencies for larger ones. Bach noted that the ability to remotely change the transmitter frequency is a convenience, because the operator does not have to leave the path in the middle of the locate in order to make the adjustment at the transmitter.

Adjusting the gain during location allows the operator to boost the signal from the transmitter, which enables the operator to follow the line a greater distance during the location. “As you walk away from your hook-up point, the signal will die over the distance,” Bach explained. By boosting the gain, the operator can compensate.

Bach said Schonstedt had worked to make the controls as user-friendly and easy to learn as possible. “There are no menus,” he said. “There are two knobs and two buttons. With a more complex control system, there’s a lot of training and a lot of learning curve.”