- Angle-based vertical offset (mm) = span(m) × 1000 × tan(angle°). This estimates how much a small angle error shifts the beam vertically across the opening.
- Voltage drop (V) = 2 × oneWay(m) × current(A) × R(Ω/m). The factor 2 accounts for the outbound and return conductors.
- Max one-way run (m) = allowedDrop(V) / (2 × current(A) × R). Use this to confirm cable sizing before pulling wire.
- Undetected zone (mm) ≈ beamHeight − minimumObjectHeight. If positive, small obstacles could pass under the beam without detection.
- Measure your opening width and planned mount heights.
- Select the sensor type that matches your door and safety plan.
- Enter your cable run as the real routing distance, not a straight line.
- Set allowances for slack and conduit to avoid short pulls.
- Fill in voltage, current, and your drop limit.
- Click Calculate to see placement checks, cable gauge, and budget values.
- Use Download CSV or Download PDF for records.
| Scenario | Type | Width (m) | Mount (mm) | Run (m) | Supply (V) | Suggested AWG | Notes |
|---|---|---|---|---|---|---|---|
| Residential single | Photoelectric | 2.6 | 125 / 125 | 10 | 24 | Auto | Standard beam height and short run. |
| Wide workshop | Reflective | 4.5 | 140 / 140 | 25 | 24 | Auto | Use higher range to resist dust. |
| High dust bay | Photoelectric | 3.2 | 110 / 120 | 35 | 24 | 16 | Check alignment and sealed housings. |
| Position monitoring | Magnetic | 3.0 | 2050 / 2050 | 18 | 12 | 18 | For open/close status, not entrapment. |
| Industrial safety edge | Pressure edge | 4.0 | — | 30 | 24 | Auto | No beam alignment; verify edge response. |
Sensor Placement Targets
For photoelectric and reflective devices, a common safety-beam band is 100–150 mm above finished floor to catch low obstacles early. When the beam is higher, small items can pass beneath before the operator reacts. Use the calculator’s undetected-zone estimate to compare mount heights against a minimum object height such as 50 mm or 75 mm.
Alignment and False-Trip Control
A small angular error can translate into a measurable vertical shift across the opening. The calculator models this using span × tan(angle), helping you see when bracket twist or uneven jambs may cause intermittent dropouts. If your range margin is tight, minor misalignment, vibration, or dust can increase nuisance reversals during peak traffic.
Cable Sizing and Voltage Integrity
Long runs and higher current draw increase voltage drop, which can reduce sensor headroom and create erratic signaling. This tool uses a loop-length method (out-and-back conductors) and compares the computed drop to your allowable percentage. If the drop exceeds the limit, shorten the route, lower current, increase supply voltage, or select a thicker cable gauge.
Environmental Derating and Enclosure Selection
Dust, glare, and temperature swings can degrade optical performance. Higher ambient light levels benefit from sunshields or hooded brackets, while dusty bays may require sealed housings and regular lens cleaning intervals. Use the exposure notes to justify an indoor-rated device versus a higher protection rating when the site includes overspray, washdowns, or direct sunlight.
Cost Planning and Commissioning Checklist
Budgeting improves when material and labor are estimated per door and scaled across the site. Example input set: width 3.0 m, mounts 125/125 mm, cable run 12 m, slack 10%, supply 24 V, current 80 mA, and allowable drop 5%. After calculating, record the suggested gauge, voltage at device, and risk flags, then verify reversing function and obstruction response during commissioning.
1) What does the “undetected zone” mean?
It estimates how much clearance exists under a beam compared to your minimum object height. A larger value means smaller obstacles may pass under without breaking the beam.
2) Why does the voltage-drop formula use a factor of two?
Most sensor circuits use two conductors for the outbound and return path. The current flows through both, so the effective electrical length is doubled for drop calculations.
3) Should I always rely on auto-select cable gauge?
Auto-select is a fast starting point. Confirm conductor type, temperature rating, and local wiring rules. If you share power with other loads, enter the combined current for a safer result.
4) How do I choose between photoelectric and reflective sensors?
Photoelectric pairs are robust across wide openings but need two heads. Reflective setups use one head and a reflector, which can be simpler but may be more sensitive to glare and alignment.
5) What mounting height is typical for safety beams?
Many installations target roughly 100–150 mm above finished floor for beam sensors. Always follow the operator and sensor manufacturer guidance and any local safety requirements.
6) Why do dust and ambient light matter so much?
Dust can attenuate or scatter the beam, while bright sunlight can reduce optical contrast. Both increase dropout risk and false trips, especially when range margin is small.
7) Is a magnetic sensor enough for safety compliance?
Magnetic sensors are great for position monitoring, but they are not a substitute for entrapment protection devices. Use the correct safety system required for the door operator and site.