Koyo TRD-NA256PW Absolute Rotary Encoder — 256 PPR Gray Code, PNP Open Collector, IP65

Knowing exactly where a shaft is — not just how far it's moved, but its precise position at this very moment — is the difference between absolute and incremental feedback. The Koyo TRD-NA256PW is an absolute rotary encoder that outputs an 8-bit Gray code position word at every moment of rotation, giving your control system real angular position data without requiring a homing sequence after every power cycle.

Built to Koyo Electronics' medium-duty TRD-NA series standard, this encoder is a clean, reliable choice for industrial positioning, conveying, and motion control applications that demand true absolute position feedback with a robust physical design.

Absolute vs. Incremental — The Practical Difference

An incremental encoder counts pulses from wherever it started. Cut power, and that reference is lost. The machine needs to home before it can do anything useful.

An absolute encoder like the TRD-NA256PW assigns a unique output code to every angular position across the full 360° rotation. Power it up cold, and the controller already knows where the shaft is standing — no motion, no homing, no waiting. For equipment that operates in environments with frequent power interruptions or where automatic re-homing is impractical or unsafe, this distinction is operationally significant.

Technical Specifications

Gray Code Output — Why It Matters

The TRD-NA256PW uses Gray binary code (also called reflected binary code) rather than standard binary. This isn't arbitrary. In a standard binary encoder, transitioning between positions can require multiple output bits to change simultaneously — and if they don't all switch at exactly the same instant due to component tolerances, the controller briefly sees a false intermediate code.

Gray code eliminates that problem. Between any two adjacent positions, only one bit changes at a time. There is no ambiguous intermediate state. For controllers reading encoder position in real time, this translates to cleaner, glitch-free position data — especially at the boundaries between code values.

PNP Open Collector Output

The PNP (sourcing) open collector configuration sources current to the load, making the TRD-NA256PW the right choice for PLC input modules and controllers configured for PNP sensors — the predominant standard across European and much of Asian industrial automation equipment.

The output can sink up to 32 mA with a residual voltage under 0.4 V at currents up to 16 mA. The 8-bit parallel output presents one wire per bit, with the most significant bit (MSB) and least significant bit (LSB) clearly defined in the wiring table for straightforward integration.

Note: If your application requires NPN (sinking) output, the TRD-NA256NWD covers the same 256 PPR specification with NPN open collector output.

IP65 — Built for the Factory Floor

The IP65 rating means the TRD-NA256PW is fully sealed against dust ingress and protected against water jets from any direction. It won't be troubled by coolant mist in a machining environment, wash-down cycles in food processing, or the general airborne contamination common in manufacturing facilities.

Koyo's TRD-NA housing takes this a step further with a 50 mm diameter die-cast body and an 8 mm solid shaft designed to accept both radial loads (up to 50 N) and axial loads (up to 30 N) — load capacity well above what many encoder applications actually impose, which contributes to a long bearing service life in real installations.

Mounting Flexibility

The TRD-NA256PW can be mounted in any orientation — vertical, horizontal, or inverted — without affecting performance. It is compatible with Koyo's NM-9D mounting clamp, NF-55D flange, and JT-035D mounting bracket accessories, giving engineers multiple installation options depending on whether the encoder is mounting to a servo motor, a conveyor shaft, a worm gearbox, or any other rotating component.

Cable exit is radial (side exit), which simplifies cable routing in tight panel or enclosure installations.

Where the TRD-NA256PW Gets Deployed

Conveyor and material handling — position tracking on indexing tables and rotary transfer systems where shaft position must be known after every stop

Packaging machinery — cam-follower position monitoring and rotary dispensing head alignment

Industrial automation — robot joint position feedback in systems requiring absolute position at power-up

Textile and winding equipment — rotary position control for take-up reels, let-off systems, and traverse guides

General machine tools — rotary table index position, tailstock position, and turret indexing confirmation

FAQ

Q1: What is the resolution of the TRD-NA256PW, and what does 8-bit mean in practice?

The TRD-NA256PW provides 256 distinct positions per revolution, which is an 8-bit Gray code output. This means the encoder divides each full rotation into 256 equal steps, with each step representing approximately 1.4° of shaft rotation. The 8-bit output occupies 8 wires in the parallel output cable, each corresponding to one binary bit of the position word.

Q2: Does this encoder need a homing routine after power-up?

No. Because it is an absolute encoder, the TRD-NA256PW outputs the correct shaft position code immediately at power-up — no motion is required to establish position. After powering on, Koyo recommends waiting at least 0.5 seconds before reading the output to allow the circuitry to stabilize.

Q3: What is the difference between the TRD-NA256PW and the TRD-NA256NWD?

Both are 256 PPR absolute Gray code encoders with the same mechanical specifications and IP65 rating. The difference is output type: the TRD-NA256PW has PNP (sourcing) open collector output, while the TRD-NA256NWD has NPN (sinking) open collector output. Select the version that matches your PLC or controller's input configuration — PNP for sourcing inputs, NPN for sinking inputs.

Q4: What is the maximum operating speed for the TRD-NA256PW?

The encoder is rated for 3,000 rpm continuous and 5,000 rpm momentary. There is also an electrical speed limit determined by the resolution and response frequency: for 256 PPR at the 20 kHz maximum response frequency, the electrical maximum speed is approximately 4,688 rpm. In practice, the lower mechanical limit of 3,000 rpm (continuous) governs normal operation.

Q5: Can the TRD-NA256PW be used outdoors or in wet environments?

The IP65 protection rating covers it against dust ingress and water jets, making it suitable for indoor washdown environments, coolant-exposed machine tools, and similarly demanding industrial settings. It is not rated for continuous immersion or outdoor exposure to direct precipitation without additional enclosure protection. Operating temperature range is −10 °C to +60 °C.