How is protective height related to beam count and pitch?

For the DQA/DQT catalogue convention illustrated here, H = (n − 1) × K calculates first-to-last-beam span, with K the beam pitch. It is not a universal manufacturer's protective-height definition. Use declared active-field dimensions for coverage and certified detection capability separately for hazard selection and positioning.

What is the difference between protective height and total length?

Protective height is the active detection zone; total mechanical length includes the housing, end caps and connectors beyond the first and last beam. When checking that a curtain fits a frame, use the total length, but when checking that it covers the hazard, use the protective height.

How do I choose protective height for different hazards?

Select the documented detection capability for the reachable hazard, then the declared active height and mounting arrangement needed to cover access. Beam pitch alone does not prove finger, hand or body protection. The numerical examples illustrate dimensional arithmetic, not approved machine designs.

Does the protective height have to cover the whole opening?

Yes. Any gap above or below the detection field is an unguarded path to the hazard. The protective height should span at least the full hazardous opening, and access from above, below or around the field must be addressed separately in the risk assessment.

How to Choose the Effective Protective Height of a Safety Light Curtain — Using DAIDISIKE DQA & DQT as Examples

Content updated: 6 September 2026

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 catalogue beam-span convention:

Core formula — H = (n − 1) × K
where H = effective protective height, n = number of beams, K = beam pitch. Declared detection capability is a separate specification and must not be inferred from pitch alone.

Compare the light curtain resolution and protective-height options after defining the opening and access paths. ISO 13855:2024 addresses safeguard positioning; a correct beam-count calculation alone does not establish safe positioning or prevent reaching over, under or around the field.

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.

DAIDISIKE DQA/DQT dimensions and protective height (H) reference

2) Selection workflow (5 steps)

Define the protection objective (choose K): Check declared finger/hand detection capability or the relevant whole-body beam arrangement; pitch alone is not an application approval. Check the chosen family and beam-count range against its current model table; do not assume DQT is limited to coarse beams.
Measure the opening that must be blocked by the field. This is the minimum required protective height H_req.
Compute the beam count: use n = ⌈H_req / 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.

Selection method for DAIDISIKE DQA/DQT light curtains

3) Worked examples with DQA/DQT

These are dimensional examples, not approved press or cell designs. Confirm model availability, declared detection capability, machine stopping capability and the applicable machine-specific safeguarding requirements before procurement.

Example A — Finger protection on a small press

Assumed catalogue pitch for this dimensional example: K = 14 mm. Finger protection requires separately documented detected-object capability; no DQA-14 order code is established by this example.
Measured opening to cover: H_req = 400 mm.
Beam count: n = ⌈400/14⌉ + 1 = 29 + 1 = 30.
Result: H = 14 × (30 − 1) = 406 mm. Select only an available model whose documented active field and detection capability satisfy the requirement; the arithmetic does not establish a catalogue order code.

Example B — Hand protection on a power press throat

Assumed pitch: K = 30 mm. Verify the exact model's hand-detection capability separately before using this dimensional result.
H_req = 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 × (26 − 1) = 750 mm field (covers the opening with margin).

Example C — Perimeter/body detection on a large cell

Assumed pitch: K = 40 mm. Whole-body entry coverage still depends on the actual field position, detected-object capability and bypass prevention.
H_req = 1,600 mm.
n = ⌈1600/40⌉ + 1 = 40 + 1 = 41 → choose next catalog size n = 42.
Result: H = 40 × (42 − 1) = 1,640 mm.

Example D — High opening with coarse resolution

Assumed pitch: K = 80 mm. This dimension calculation does not approve an aisle-protection layout or its beam geometry.
H_req = 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 ≈ 5–40 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.

Rule of thumb for fit: 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 detection capability first, then use the catalogue pitch for height calculations. Fine and coarse pitches are not interchangeable guarding approvals.
Round up, never down. When H_req/K is 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 positioning separately under the applicable ISO 13855:2024 method. The historical S = K × T + C expression uses K for approach speed, not the beam pitch K in this article. Height arithmetic alone is not a complete protective-distance calculation.

6) Quick reference table (K & typical P/J)

Beam pitch 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	Confirm drawing	Confirm drawing	DQA	Special beam arrangement; verify application

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; whether the family changes depends on the actual catalogue options. Recheck declared detection capability and safety positioning separately.

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.

Light Curtain Demo Videos (YouTube)

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