The Topcon LS-100D is a digital grade laser receiver designed for machine control on excavators, motor graders, and scrapers. It turns any Topcon rotary grade laser into a single-operator system — the receiver mounts on the machine, the operator reads the cab display, and no rod person is needed in the trench or cut. This guide covers how the LS-100D works, mounting procedures for different machines, accuracy specifications, and compatible grade lasers.
The LS-100D is the digital version of Topcon's LS-80 series grade rod receivers. Unlike the LS-80L (a hand-held rod receiver for survey work), the LS-100D is purpose-built for machine mounting. It adds a numeric digital readout showing the exact deviation in millimeters or hundredths of a foot, plus a Bluetooth wireless output for sending grade data to cab displays and data collectors.
In a typical machine control laser setup, the grade laser (RL-H5A or RL-HV2S) sits on a tripod at a known elevation on the edge of the site. The LS-100D mounts on the excavator boom or grader blade pole. As the machine moves through the cut, the LS-100D continuously reads its height relative to the laser plane. The cab display shows the operator whether the bucket is above or below grade — and by exactly how much — in real time.
This eliminates the rod person who would otherwise stand in the trench, hold a grade rod, and yell cut or fill instructions to the operator. On straight-grade earthwork — residential foundations, drainage ditches, rough subgrade — laser machine control with the LS-100D consistently delivers more production per day and tighter as-built grades than traditional rod-and-level methods.
Key specifications for the LS-100D receiver when used in machine control applications.
| Detection Accuracy | ±1mm (±0.003 ft) | With compatible Topcon grade laser at rated range |
| Detection Window | 165mm (6.5 inches) | Tall window for fast laser acquisition on moving machine |
| Working Range | Up to 400m from laser | With Topcon RL-H5A or RL-HV2S |
| Display | LED bar graph + numeric deviation | Shows mm or ft/hundredths deviation |
| Output | Bluetooth wireless | Connects to cab display or data collector wirelessly |
| Cable Output | RS-232 serial | For wired cab display connection |
| Laser Wavelength | 630–680nm (visible red) | Compatible with most visible red rotary lasers |
| Operating Temp | -20°C to +50°C | Full outdoor temperature range |
| IP Rating | IP54 | Dust and splash resistant for machine mounting |
| Battery | 4× AA alkaline | 80+ hours operation |
| Weight | 420g (0.9 lbs) | Light enough for boom-mount without counterbalance |
| Mount | Adjustable pole bracket (included) | Fits 1" to 1.5" diameter poles and masts |
Correct mounting is critical to accurate readings. The receiver must be positioned where the laser plane can intersect the detection window throughout the full range of machine movement.
Mount the LS-100D on the excavator boom stick using the pole bracket. Position the receiver approximately 1.5–2 meters above the bucket pin. This keeps the receiver in the laser plane when the bucket is at design subgrade depth. Run the cable (or use Bluetooth) to a cab-mounted display such as the Topcon CB-3. Calibrate the system by setting the bucket tooth on a known benchmark and zeroing the cab display — this sets the relationship between bucket depth and receiver height, so the operator reads directly in cut/fill rather than receiver height.
On a motor grader, mount the LS-100D on a mast attached to the blade circle or moldboard. The mast should position the receiver at laser plane height when the blade is at design grade. Most grader operators use two receivers — one on each end of the blade — for cross-slope control. The cab display shows both sides simultaneously, allowing the operator to maintain both longitudinal grade and cross-slope with a single laser setup.
For rough-grade work with a skid steer, mount the LS-100D on a mast attached to the bucket frame. The smaller footprint and frequent direction changes of skid steers mean the receiver can lose the beam more frequently — use the audible alarm to alert the operator when the beam is lost, and position the grade laser for maximum line-of-sight coverage across the work area.
Horizontal rotary laser
The most common pairing. The RL-H5A provides a flat horizontal plane — set at subgrade design elevation. The LS-100D on the excavator reads cut/fill from that plane. Best for horizontal subgrade work: pads, foundations, parking lots.
View Topcon RL-H5A guide →Single-grade rotary laser
For grade control on sloped work — drainage ditches, swales, road subgrade. The RL-HV2S projects a tilted laser plane at the design slope. The LS-100D follows the plane through the cut, giving the operator a constant grade reference.
Dual-grade rotary laser
For complex grading with both X and Y slopes — parking lots with cross-slopes, superelevated curves, athletic fields. Two LS-100D receivers on the grader blade give real-time cross-slope and longitudinal grade simultaneously.
630–680nm rotating beam
The LS-100D will detect any visible red rotating beam in the 630–680nm range. Spectra Precision and Leica rotary lasers in this wavelength range will trigger the receiver, though digital readout accuracy is only specified for Topcon instruments.
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