Understanding Rangefinder Accuracy Specs: ±m vs %
Look closely at any accuracy line on our spec sheets and you'll notice it's rarely a single number. Our flagship LRF3000A1 reads: d ≤ 100 m: ±0.7 m · d > 100 m: ±(0.7 + 0.003·d) m. The LR2000E2 reads: ±1 m (≤400 m) · d·0.4% (400–2,000 m). That's not inconsistent labeling — it's an honest description of how ranging error actually behaves with distance, and reading it correctly matters more than the headline "±1 m" most people quote.
Two error sources, two terms
A DToF measurement's error has two distinct physical sources, and each dominates in a different part of the range envelope:
| Fixed / near-range term | Set mainly by the timing resolution of the receiver electronics and small calibration residuals. At short range the return signal is strong, so this fixed floor — not signal noise — is the limiting factor. It shows up as a flat ± figure (e.g. ±0.7 m, ±0.3 m, ±1 m) that doesn't change much across the near part of the range. |
|---|---|
| Proportional / far-range term | As distance grows, the return signal weakens — for a point-like target it falls off roughly with the square of the distance — so the timing measurement gets noisier and ranging error grows with it. That's modeled as a per-metre slope or a percentage of distance, added on top of the fixed floor once you cross the stated threshold. |
What it means at your actual operating distance
Take the LRF3000A1's formula literally at its rated maximum: ±(0.7 + 0.003 × 3000) m ≈ ±9.7 m at 3,000 m. That's not a hidden flaw — it's the formula being honest about physics you can't get around with better electronics alone. The point is: don't design your system around the best-case near-range figure if you're actually going to operate near the top of the module's range. Always compute the formula at your longest expected working distance, then decide if that error budget fits your application.
Accuracy isn't the only number that matters
Three other figures on the same spec sheet answer questions accuracy alone doesn't:
- Resolution — the smallest distance increment the module can report (typically 10 cm or 20 cm across our line). This bounds precision even where accuracy is good; you won't see finer distinctions than the resolution allows.
- Valid measurement rate — the share of shots that return a usable reading at all (≥ 98% on our modules, under the datasheet's reference conditions). A module can be accurate when it returns a reading and still leave you with occasional dropouts if this figure is low.
- False alarm rate — the probability of a reading that looks valid but isn't (≤ 1% across the line). This is a data-integrity concern separate from accuracy: an accurate module with a poor false-alarm rate will occasionally hand your system a confidently wrong number.
A real example: static vs dynamic accuracy
Our SPD1200S2G — a distance-plus-gyroscope module built for moving platforms — publishes something most spec sheets don't: separate error figures for static and dynamic operation. Its radial distance error (two-point measurement) is quoted at ±1 m up to 500 m and ±(1 + d·0.1%) beyond; but its static distance error is ≤ ±1 m under 100 m, ≤ ±3 m from 100–500 m, ≤ ±5 m from 500–1,000 m — and its dynamic distance error (measured while the platform is moving) opens further still: ≤ ±1 m under 50 m, ≤ ±3 m from 50–100 m, ≤ ±6 m from 100–500 m, ≤ ±10 m from 500–1,000 m. That spread exists because platform motion during the measurement window adds its own uncertainty on top of the optical ranging error — exactly the kind of real-world condition a headline accuracy figure never captures. If your platform moves while it ranges, budget against the dynamic figure, not the static one.
Conditions the datasheet already assumes
Every accuracy and range figure on our sheets is quoted against a specific reference: a stated target reflectivity (commonly a 70% or 90% reflectivity reference surface), clear-air visibility, and normal incidence. Lower reflectivity, poor visibility, a steep angle of incidence, or a very small target will all reduce real-world range and can widen effective error beyond the datasheet figure. Validate against your own target and environment before you lock in a design margin — the datasheet gives you the physics-limited best case to design toward, not a guarantee under every condition.
The practical rule
Read the accuracy line as a formula, not a headline number. Identify which distance band you actually operate in, compute the error at your farthest working point, and cross-check it against resolution and valid measurement rate for the full picture. Every model's full formula is on its own spec sheet in the module catalog — if you're not sure which band applies to your platform, send us the numbers in an RFQ and we'll help you read it.