Quick Answer
What is the Topcon AT-B4A?
See also: Leica NA524 Automatic Level Specs
See also: Sokkia B40 Automatic Level Specs
The Topcon AT-B4A is a 28× automatic level with 1.5mm/km accuracy (standard deviation per km double-run leveling). It is a mid-range optical level suited for construction grade checks, floor levelness surveys, and utility layout work.
Topcon AT-B4A Automatic Level — Complete Specs, Manual & Guide
Category: Automatic Level | Brand: Topcon | Model: AT-B4A
The Topcon AT-B4A is a reliable automatic level for construction and light surveying applications. With a 28× magnification and ±1.5mm/km accuracy, it handles floor slab surveys, foundation benchmarks, and site control leveling. The pendulum compensator self-levels within ±15 arc minutes, and the sealed optical system resists dust and moisture for daily outdoor use.
Topcon AT-B4A Full Specifications
| Telescope magnification | 28× |
| Accuracy (std dev per km) | ±1.5mm/km |
| Compensator type | Magnetic damped pendulum |
| Compensator range | ±15 arc minutes |
| Shortest focusing distance | 0.5m |
| Field of view at 100m | 1°20' / 2.4m |
| Objective aperture | 36mm |
| Stadia ratio | 100:1 |
| Plate vial sensitivity | 8'/2mm |
| Circular vial sensitivity | 10'/2mm |
| Tripod thread | 5/8" × 11 |
| Weight | 1.7 kg (3.75 lbs) |
| Operating temperature | -20°C to +50°C |
Accessories & Part Numbers
- TK-26 — Topcon hard case compatible with AT-B4A
- TS-1 — Tribrach and base adaptor
- Standard grade rod — Any 5m or 7m telescoping rod compatible
- Sunshade — Fits standard Topcon telescope barrel
Frequently Asked Questions — Topcon AT-B4A
What is the accuracy of the Topcon AT-B4A?
The AT-B4A achieves ±1.5mm standard deviation per kilometer of double-run leveling under standard field conditions. This is suitable for construction benchmarks, floor surveys, and utility grade checks — but not for precision geodetic control work, which requires a digital level with sub-millimeter accuracy.
What is the magnification of the Topcon AT-B4A?
The AT-B4A features a 28× telescope with a 36mm objective aperture. This gives clear rod readings at typical construction survey distances of 30–80m. The maximum practical sight distance for accurate readings is approximately 100m in good lighting conditions.
How does the AT-B4A compensator work?
The AT-B4A uses a magnetic-damped pendulum compensator that automatically levels the line of sight within ±15 arc minutes of the instrument's bubble center. Once the circular vial bubble is centered, the compensator maintains a level reference line without further adjustment.
What is the difference between the Topcon AT-B4A and AT-B3A?
The AT-B3A is Topcon's higher-accuracy automatic level at ±1.0mm/km, compared to ±1.5mm/km for the AT-B4A. Both have 28× magnification. The AT-B3A is preferred for structural settlement monitoring and precision foundation surveys; the AT-B4A is the workhorse choice for routine construction grading.
Can the AT-B4A read barcoded leveling rods?
No — the AT-B4A is an optical level requiring manual rod reading. For automatic electronic rod reading (barcode rods), a digital level such as the Topcon DL-503 is required.
Related models: Leica NA524 | Sokkia B40 | Topcon DL-503 Digital Level
Track your Topcon AT-B4A calibration and service records with Gradelog's Equipment Registry. Free to start at gradelog.com.
