How to Choose the Effective Protective Height of a Safety Light Curtain — Using DAIDISIKE DQA & DQT as Examples
Goal: help engineers and buyers determine the right effective protective height for a safety light curtain so the opening is fully guarded and the device fits your machine. The method below is based on DAIDISIKE’s DQA/DQT families and uses the standard industry definition:
H = (n − 1) × Kwhere H = effective protective height, n = number of beams, K = beam spacing (resolution).
1) What exactly is “H” and what it is not
Effective protective height (H) is the active sensing field height formed by the outermost usable beams. When an object blocks any beam, the curtain switches its OSSD outputs and the machine must stop. H does not include the top/bottom mechanical margins of the housing.
For DAIDISIKE light curtains, H is determined by the beam count and spacing: H = (n − 1) × K. For example, with K = 14 mm and n = 30, H = 14 × 29 = 406 mm.
2) Selection workflow (5 steps)
- Define the protection objective (choose K): Finger → 10–14 mm; Hand → 20–30 mm; Body/area → 40–200 mm. DQA covers 10–30 mm; DQT covers 40–200 mm and long-range fields.
- Measure the opening that must be blocked by the field. This is the minimum required protective height
Hreq. - Compute the beam count: use
n = ⌈Hreq / K⌉ + 1. (Always round up so the field fully covers the opening.) - Pick the nearest catalog model in the DQA/DQT list with that n and K. If the exact beam count is not offered, select the next larger H.
- Verify mechanical fit: the overall product length is approximately
L = P + H + J + 18 mm + 18 mm. Ensure mounting space allows the housing, brackets, and cable bend radius.
3) Worked examples with DQA/DQT
Example A — Finger protection on a small press
Example B — Hand protection on a power press throat
- Objective: palm/wrist → K = 30 mm (DQA).
- Hreq = 720 mm.
n = ⌈720/30⌉ + 1 = 24 + 1 = 25→ use the next available size if catalog uses even counts, e.g. n = 26.- Result: H = 30 × 25 = 750 mm field (covers the opening with margin).
Example C — Perimeter/body detection on a large cell
- Objective: body/area isolation → K = 40 mm (DQT).
- Hreq = 1,600 mm.
n = ⌈1600/40⌉ + 1 = 40 + 1 = 41→ choose next catalog size n = 42.- Result: H = 40 × 41 = 1,640 mm.
Example D — High opening with coarse resolution
- Objective: aisle entry detection → K = 80 mm (DQT).
- Hreq = 1,200 mm →
n = ⌈1200/80⌉ + 1 = 15 + 1 = 16. - Result: H = 80 × 15 = 1,200 mm.
4) Mechanical fit: P / J and total length L
DAIDISIKE drawings show two small fixed margins outside the active field:
- P — top offset from housing edge to the first active beam.
- J — bottom offset from the lowest beam to housing edge.
Typical values (from DQA/DQT dimension tables) are around P ≈ 5–20 mm depending on K, and J ≈ 25–32 mm. Always check the exact datasheet for the selected model. These margins matter when you must align the field with a guard opening or table surface.
L ≈ P + H + J + 36 mm (adds 18 mm end caps at top and bottom). Verify bracket space and cable exit.5) Practical tips & checks
- Choose the resolution first (10–14 mm finger, 20–30 mm hand, 40–200 mm body). This decides K and the product family (DQA vs DQT).
- Round up, never down. When
Hreq/Kis not an integer, take the next larger beam count. - If the catalog lists even beam counts only, pick the next even n above your calculation.
- Mind mirrors and muting: mirrors don’t change H but increase alignment and cleaning needs; muting/blanking doesn’t relax H requirements.
- Check safety distance separately with
S = K × T + Cper ISO 13855; H covers height, while S covers approach time to stop.
6) Quick reference table (K & typical P/J)
| Resolution K (mm) | Typical top offset P (mm) | Typical bottom offset J (mm) | Main series | Typical use |
|---|---|---|---|---|
| 10 | 5 | 32 | DQA | High-risk finger zones |
| 14 | 7 | 32 | DQA | Finger guarding (global mainstream) |
| 20–30 | 10–15 | 25 | DQA | Hand/palm guarding |
| 40 | 20 | 25 | DQT | Body/area detection |
| 80 | 40 | 25 | DQT | Perimeter/aisle entry |
| 200 | 20 | 25 | DQT | Wide-beam area protection |
FAQ
Q1. Does H need to equal the opening height exactly?
A. No. H must be greater than or equal to the opening. When your calculation lands between catalog sizes, select the next larger H.
Q2. If I change K, do I have to recalc everything?
A. Yes. K directly multiplies into H via H = (n − 1) × K. Changing K changes the required n and the product family (DQA vs DQT).
Q3. Do P and J change the effective height?
A. P and J are mechanical margins; they do not add to H. Use them to check fit and to set the field exactly where protection is needed.