DD-T21 / DD-T31 / DD-D21 Built-in Amplifier Photoelectric Switch
One part per detection point: the amplifier lives inside the head, so you wire 12–24 VDC and start detecting — no external amplifier box, no extra rail space.
- Through-beam 1.5 m (DD-T21) or 2.5 m (DD-T31), infrared
- Diffuse 150 mm with sensitivity trimmer (DD-D21)
- NPN NO output, 1 ms response
- Detects targets down to 6 mm
- 20 mA max. draw — friendly to multi-point layouts
Product Overview
The DD-T21, DD-T31 and DD-D21 form a compact photoelectric switch family aimed at machine builders who ship equipment with many simple detection points. Instead of pairing a fiber-optic head with a separate amplifier unit, each of these sensors carries its amplifier inside the housing: connect a 10.8–26.4 VDC supply and the NPN normally-open output is ready for your PLC input.
Two sensing philosophies are covered. The DD-T21 (1.5 m) and DD-T31 (2.5 m) are infrared through-beam emitter/receiver pairs — the most robust choice when both sides of a gap are reachable. The DD-D21 is a diffuse-reflective unit rated 150 mm, mounted on one side only, with an on-body sensitivity control for tuning against changing target and background reflectivity.
With a 1 ms response, a 6 mm minimum detectable object and a maximum draw of just 20 mA, the series suits fast small-part counting and multi-point layouts inside dry, indoor equipment enclosures (IP40).
Two Sensing Modes, One Wiring Concept
Rule of thumb: reach both sides of the gap → through-beam (DD-T21/T31); one side only → diffuse (DD-D21).
Model Selection Table
| Model | Sensing Mode | Sensing Distance | Light Source | Output | Sensitivity Adjustment |
|---|---|---|---|---|---|
| DD-T21 | Through-beam (emitter + receiver) | 1.5 m | Infrared | NPN NO | — |
| DD-T31 | Through-beam (emitter + receiver) | 2.5 m | Infrared | NPN NO | — |
| DD-D21 | Diffuse-reflective (single side) | 150 mm | Contact factory | NPN NO | On-body trimmer |
PNP or normally-closed variants are not confirmed in current factory data — contact the factory before specifying them.
Technical Specifications
| Models | DD-T21 / DD-T31 / DD-D21 |
|---|---|
| Sensing method | DD-T21 / DD-T31: through-beam; DD-D21: diffuse-reflective |
| Sensing distance | DD-T21: 1.5 m; DD-T31: 2.5 m; DD-D21: 150 mm (adjustable sensitivity) |
| Light source | Infrared (through-beam models); DD-D21 source — contact factory |
| Output | NPN, normally open (NO) |
| Supply voltage | 10.8 – 26.4 VDC (nominal 12 – 24 VDC) |
| Current consumption | 20 mA max. |
| Response time | 1 ms |
| Minimum detectable object | 6 mm |
| Protection rating | IP40 — dry indoor environments only |
| Operating temperature / cable spec | Contact factory |
General-purpose sensing component — not an IEC 61496-certified safety component; never use it alone for personnel protection.
Typical Applications
Point Detection Inside OEM Machines
Slips into cramped mechanism bays where a fiber head plus DIN-rail amplifier will not fit — one part, one cable, done.
Conveyor Gap Sensing up to 2.5 m
DD-T21 (1.5 m) and DD-T31 (2.5 m) beam pairs cover typical narrow and mid-width belt crossings.
Carrier & Tray Confirmation
1 ms response and 6 mm minimum target catch fast-moving small carriers on electronics assembly lines.
Multi-Point Budget Layouts
At 20 mA per head, dozens of detection points can hang off one 24 VDC rail without power-budget headaches.
Frequently Asked Questions
Why choose an amplifier-built-in photoelectric switch over a fiber head with a separate amplifier?
Every fiber-optic sensing point costs you a fiber head, an amplifier unit, DIN-rail space and two wiring runs. The DD-T21/T31/D21 puts the amplifier inside the sensing head, so each point is one part and one 12-24 VDC cable. For exporters and OEM machine builders shipping equipment with many simple on/off detection points, that cuts BOM lines, panel space and assembly minutes per machine.
Which model do I pick — DD-T21, DD-T31 or DD-D21?
Use the through-beam pairs when you can mount hardware on both sides of the gap: DD-T21 for spans up to 1.5 m, DD-T31 up to 2.5 m; both use an infrared emitter/receiver pair. Use DD-D21 when only one side is reachable — it is diffuse-reflective, rated 150 mm, with an on-body sensitivity trimmer to tune out background reflections.
What output logic does this series provide?
All three models are NPN, normally-open (NO). No PNP or normally-closed variant is confirmed in the current factory data — if your PLC input card is sourcing (PNP), tell us at enquiry stage and we will point you to a suitable alternative series.
How fast is the response, and how small a target can it see?
Response time is 1 ms across the series, and the minimum detectable object is 6 mm. That is fast enough for counting small parts passing at typical conveyor speeds without missed pulses.
Can I use it outdoors or in washdown areas?
No. The housing is rated IP40 — protected against solids over 1 mm but not against water. Keep it inside dry, indoor machine enclosures. For wet or washdown stations, ask us about IP65/IP67-rated photoelectric alternatives.
Is this a safety component for guarding operators?
No. The DD-T21/T31/D21 series is a general-purpose sensing component, not an IEC 61496-certified safety component, and must never be used on its own for personnel protection. For guarding, use a certified safety light curtain such as our DQC series.
What is the MOQ and lead time for export orders?
Small trial quantities are usually workable, and standard models normally ship quickly from factory stock in Foshan. MOQ, lead time and packaging for your exact model mix are confirmed at quotation — contact us with your model list and destination port.
Do you supply datasheets and certification documents?
Yes — dimensional drawings, wiring diagrams and available certification documents are provided on request with your enquiry. Parameters not published on this page (operating temperature range, cable specification, source wavelength) should be confirmed with the factory rather than assumed.
Specs reviewed by Engineer Cai, Senior Application Engineer. See certificates.