Measuring Light Curtains

Analog / RS485 / switching measuring light curtains for dimensioning, counting and vehicle separation.

DQL Measuring Light Curtain (Analog/RS485)

Measuring light curtain with dual analog (voltage / 4-20mA current) and RS-485/RS-232 Modbus RTU serial output, 1.25-80mm beam spacing.

DQLV Vehicle Separation Light Curtain

Vehicle-separation through-beam curtain that deliberately ignores anything under 150 mm -- birds, insects, glare -- while resolving to 1 mm, with a controller-free NPN/PNP/relay/RS-485 output built for toll, parking and gate lanes.

DQM Measuring Light Curtain (Switching Output)

Switching-output measuring light curtain: any interrupted beam triggers direct NPN/PNP output, no controller needed.

Measuring, Not Guarding — What These Light Curtains Are For

A measuring light curtain looks exactly like its safety cousin — two aluminium profiles, a fence of infrared beams between them — but it answers a completely different question. A safety curtain asks *"is something in the opening?"* and stops a machine. A measuring curtain asks *"how tall, how wide, where, and how many?"* and reports the answer to your PLC as data. The DQL, DQM and DQLV series on this page carry no IEC 61496 Type rating and no ISO 13849 category, deliberately: they are measurement and detection instruments, and we say so plainly rather than dressing them in safety language.

That makes this the right page if you searched for a non safety light curtain, a light grid sensor, or an infrared curtain for dimensioning, profiling, counting, hole detection or vehicle separation. If your application must protect people — stopping a press when a hand enters — leave this page now and specify from the safety light curtain category instead; no measuring product belongs in a personnel-protection circuit.

Principle diagram of a measuring light curtain converting blocked infrared beams into data: full beam bitmap mode and highest-lowest-count edge mode sent to a PLC — Two frame formats: the full beam bitmap, or just the edges and count — object height and position in a single frame.

DQL vs DQM vs DQLV: Choose by Output, Not by Looks

All three series share the same optical platform; what you are really ordering is an output philosophy. If your controller wants an analogue level or a serial telegram, that is the DQL. If you want plain switching outputs with no controller in between, that is the DQM. If the job is separating vehicles in a lane, the DQLV is a purpose-built variant with its own logic.

Attribute	DQL	DQM	DQLV (vehicle)
Output	4–20 mA current, voltage output, or RS-485/232	NPN or PNP switching, direct	vehicle-separation logic outputs
Protocol	Modbus RTU (customised frames)	—	—
Finest beam pitch	1.25 mm	2.5 mm	fixed 1 mm-resolution grid
Max beams / height	496 beams / 3990 mm	per model table	up to 1420 mm
Response	per configuration	catalogue lists differing values — confirm at order	≤ 15 ms
Special ability	push frames every 100 ms or polled multi-drop	no controller needed at all	ignores anything under 150 mm by design
Environment	IP65 (IP68 as DQLF)	IP65 (IP68 as DQMF)	IP67 + optional heater hood

Comparison chart of DAIDISIKE DQL analog RS-485 measuring light curtain, DQM switching output light grid and DQLV vehicle separation light curtain — Same optics, three output philosophies — the deciding question is what your control system accepts.

Tell us what you are measuring — object size, line speed, and what your PLC accepts (4–20 mA, RS-485 or a dry contact) — via the inquiry form, and the reply is a full model code like DQL08/10-70.

Resolution Is Set by Beam Pitch: 1.25 mm to 80 mm

Detection resolution on a light grid is not a tuning parameter — it *is* the beam pitch you purchase. An object is registered when it fully interrupts at least one beam, so the pitch defines the smallest object the curtain can guarantee to see. The DQL's finest grade runs a 1.25 mm pitch (64 to 448 beams, with the special constraint that this grade works across 0.2–1 m ranges), resolving wire-thin edges; the DQM starts at 2.5 mm; and the ladder climbs through 5, 10, 20 and 40 mm up to 80 mm for pallet-scale profiling.

Protected heights follow the same matrix — from about 60 mm up to 3990 mm depending on pitch and beam count — so the practical selection sequence is: smallest object first (that fixes the pitch), measured span second (that fixes beam count and height), output philosophy last (that picks the series). We publish the pitch, beam count and height for every model on the three product pages; what we do not publish is any extra "precision factor" beyond the pitch, because optically there isn't one.

Resolution ladder for measuring light curtains from 1.25 mm to 80 mm beam pitch with the object classes each pitch can resolve — The pitch you buy is the resolution you get — from wire edges at 1.25 mm to pallets at 80 mm.

Analog 4–20 mA and Modbus RTU Integration

On the serial side, the DQL speaks Modbus RTU with two frame styles. Mode 1 transmits the complete beam bitmap — every beam's clear/blocked state, every cycle — which is the format for profiling and hole-detection work where the *shape* matters. Mode 2 compresses each scan to three numbers: highest blocked beam, lowest blocked beam, and total blocked count — one compact frame that yields object height, vertical position and a presence count, which covers most dimensioning and sorting jobs at a fraction of the bus load.

Delivery is either active push (the curtain transmits on its own clock, 100 ms by default) or passive polling, which lets several curtains share one RS-485 trunk and answer by address. Baud rates run 4800 to 38400. On the analogue side, 4–20 mA current output is the standard configuration; for voltage output the catalogue currently prints more than one range on different pages (1–10 V, 0–10 V and 1–5 V appear), so treat the voltage option as configure-at-order and have the factory confirm the range in writing — we would rather flag our own catalogue's inconsistency than let it surprise you at commissioning.

If the receiving end is one of our own I/O modules rather than a PLC, the relay & timer module category includes RS-485 I/O units that pair naturally with the DQL on the same bus.

Bus wiring, termination and sensor-output reference material beyond this page lives in the DAIDISIKE engineering library on fsddsk.com — this page stays at the integration level.

Vehicle Separation Lanes: Ignoring Everything Under 150 mm Is the Feature

The DQLV inverts the usual instinct that more sensitivity is better. In a toll, weigh-in-motion or access lane, the failure mode is *over*-detection: a bird crossing the grid, spray off a wheel, a dangling mudflap — any of them can split one vehicle into two transactions. So the DQLV is built to disregard objects under 150 mm outright while resolving the vehicle profile on a 1 mm grid, fast enough (≤ 15 ms) to catch the gap between a tractor and its trailer at lane speed and judge axle spacing and headway correctly.

The environmental spec follows the duty: IP67 housings, sensor operation from -10 to +55 °C, and for climates where lens icing or fog is the real enemy, the DQLV-1.6 and DQLVF-1.8 heater hoods (200 W, 24 VDC) keep the optical faces clear through winter. For counting, classing and separation duty the grid replaces buried loops without cutting the roadway.

Two applications of measuring light curtains: carton dimensioning on a conveyor with DQL analog output, and toll lane vehicle separation with DQLV ignoring objects under 150 mm — Left: DQL reports carton height to the PLC. Right: DQLV separates vehicles — birds and spray can't split a transaction.

When a Measuring Curtain Is the Wrong Device

Three honest disqualifiers. If the point of the installation is protecting a person, this category is disqualified by definition — specify from the safety light curtain range with its published Type-4 architecture instead. If your smallest object is finer than the finest pitch you can accommodate, a light grid is the wrong physics — look at the laser displacement sensors for sub-millimetre work. And if the line gets high-pressure washdown, the standard IP65 housings are not the answer: the DQLF/DQMF IP68 variants exist as special orders, but describe the washdown regime to the factory before ordering rather than after the first CIP cycle.

Frequently Asked Questions

Is a measuring light curtain a safety device?

No. The DQL, DQM and DQLV publish no IEC 61496 Type rating and no ISO 13849 category, and must never be the device that stops a machine to protect a person. For personnel protection, specify from the safety light curtain category — same optical idea, completely different engineering duty.

What is the difference between DQL and DQM?

Output only, on a shared platform. DQL carries the analogue (4–20 mA / voltage) and RS-485/232 Modbus RTU options and reaches a 1.25 mm pitch; DQM outputs NPN or PNP switching signals directly with no controller in the loop, starting at a 2.5 mm pitch.

What data can I read over RS-485?

Two frame formats: the full beam-state bitmap (Mode 1), or highest blocked beam + lowest blocked beam + blocked count (Mode 2). Frames arrive by active push — every 100 ms by default — or by passive polling, which allows several curtains on one bus, addressed individually. Baud 4800–38400.

What is the finest resolution available?

1.25 mm beam pitch on the DQL fine grade — 64 to 448 beams, protected heights 78.75 to 558.75 mm, with ranges limited to 0.2–1 m at this pitch. The DQM's finest is 2.5 mm. In every case detection resolution equals the pitch ordered.

Can the DQLV replace a buried loop for vehicle detection?

For separation, counting, classing and headway judgement in a lane — yes, without cutting the road surface. The 150 mm detection floor means birds, spray and debris cannot trigger it, and the optional 200 W / 24 VDC heater hoods keep it running through icing weather.

Measuring Light Curtains in Action — 1 Demonstration Videos

Wiring, setup and live operation filmed on the actual modules. Each clip links back to the series it demonstrates, so you can go straight from footage to specification.