Courtesy Trimble
Trimble's Digirod can measure grade from a rotating laser without ever touching the ground.

From the "groma" with its right angles and plumb bobs used 3,000 years ago to modern-day grade rods, surveyors have been using some type of rod in their work. A new grading device claims to eliminate the need for grade rods when checking grades with a rotating laser. It compounds a laser distance meter, laser receiver, tilt sensor and digital readout to get grade readings without touching the ground at tilt angles of up to 30 degrees.

Trimble Inc., Sunnyvale, Calif., calls its grading instrument, which was introduced to the market last week, the Digirod. It can emulate various grade rods, including direct elevation rods, cut/fill rods and inderect reading rods. Users must site a rotating laser beam in the device's reception window and then shoot a laser distance meter mounted on the Digirod to the bottom of, say, a trench. These measurements compute the grade.

“I love it,” says Aron Tipps, a surveyor for Ferguson Construction Co., Sidney, Ohio, who beta-tested the Digirod. “You don’t have to carry rods and a laser eye around with you.”

“You benchmark the device at the top of the ground,” says Mike Yowler, Trimble product manager. “Then, you point the laser into a trench, push the reading button, and it tells you the depth of the hole.”

The Digirod can measure elevation up to six meters, and has a five-inch vertical reception range that doesn’t require centering on-grade to get a reading from the rotating laser. Further, its laser distance meter has a 50-meter range with ±2.0 millimeters of accuracy.

“On one of the sites that beta-tested the device, we had a bulldozer operator who had worked with inches all his life and a foreman who always worked in hundredths of a foot,” says Yowler. “The device translated for them just by pushing a button.”

Since there is no rod to touch the ground, the Digirod can be used on finished surfaces, such as screeded concrete, without leaving marks. The distance to the ground and the distance to the rotating beam are measured and displayed on screen.

“We’re saving weight by not carrying the rods around, and we’re taking less notes,” says Tipps, who also uses the device to check as-builts. “It has sped up work by a good 25% to 30%.”