HeidenhainIncremental Rotary Encoder, 2540 Lines/Rev, 11 µApp Sinusoidal Output, 10 mm Solid Shaft, IP67, 12,000 rpm, 5 V Supply

Product Description

What this part is

This is a HEIDENHAIN ROD 450 incremental rotary encoder in the 2540-line build, HEIDENHAIN ID number 251 568-1N. It is a bearing-mounted incremental encoder: the shaft runs in its own bearings inside the housing and is joined to the driving shaft through a separate rotor coupling rather than being rigidly bolted to it. That coupling exists to absorb axial movement and radial and angular misalignment between the two shafts, which is what keeps the graduated disc running true and stops shaft-to-shaft error from being read as position error.

Why the 11 µA sinusoidal output is the fact that decides fit:
The ROD 450 family outputs 11 µA peak-to-peak sinusoidal current signals. It drives controls, counters and position displays that have a genuine 11 µA sinusoidal input, which is the population of older HEIDENHAIN-era CNCs, position displays and counters this encoder belongs to. For a TTL A/B quadrature input, a HEIDENHAIN EXE interface unit shapes the sinusoidal current into square-wave pulses. The upside of a sinusoidal encoder is interpolation: an analogue sinusoid can be electronically subdivided far beyond the physical line count, which is how a 2540-line disc yields resolution well finer than 2540 counts per revolution.

Decoding the two numbers on this encoder

Listings for this part show both “ROD 450-2540” and “251 568-1N”, which looks like two competing part numbers. It is not. HEIDENHAIN uses a 6-digit base ID that identifies the model and variant family, followed by a 2-character variant suffix that encodes line count, signal type, connection type and cable length. Here 251 568 is the ROD 450 base ID, and -1N is the variant code for this specific build. Two confirmed sibling variants on the same base ID make the pattern obvious.

251 568-78: ROD 450-1000.

251 568-4F: ROD 450-1800.

251 568-1N: this unit, corresponding to the 2540-line build.

So “-2540” is the designation-side line count and is not part of the ID number at all. When sourcing a match for an existing machine, quote the full ID including the suffix, because the base ID alone does not specify the encoder you will receive.

Published ratings

Type: incremental rotary encoder with integral bearing, separate rotor coupling.

Line count: 2540 lines per revolution, within the ROD 450 family range of 50 to 5000 lines per revolution.

Output signal: 11 µA peak-to-peak sinusoidal current.

Supply voltage: 5 V ±0.5 V.

Cutoff frequency at −3 dB: 160 kHz.

Shaft: 10 mm diameter solid shaft.

Reference mark: one.

Protection class: IP67.

Maximum mechanical speed: 12,000 rpm.

Operating temperature: −40 °C to +100 °C.

Accuracy: ROD 400 family positioning accuracy is quoted around ±13 arcseconds, with system accuracy of 1/20 of the grating period.

What the cutoff frequency and speed rating mean in practice:
These two numbers together set your usable shaft speed, and they do not agree. The 12,000 rpm figure is a mechanical limit — what the bearings and disc will survive. The 160 kHz −3 dB cutoff is the electrical limit on signal amplitude. At 2540 lines per revolution, 160 kHz corresponds to roughly 3,800 rpm before signal amplitude has fallen by 3 dB, so on a high line count like this one the electronics, not the bearings, are what cap the speed. A 2540-line encoder is a resolution choice, and resolution and top speed trade against each other on any incremental encoder.

Mounting data

Mounting: flange mount with integral bearing, driven through a separate rotor coupling.

Shaft: 10 mm diameter solid.

The sibling ROD 456 uses a synchro flange of Ø58 mm with a Ø42 mm bolt circle.

The ROD 450 was supplied in both cable and flange-socket versions, in radial and axial orientations; the photographs show which this unit is.

Quantity and configuration

Unit Quantity: 1 encoder. The rotor coupling that joins the encoder shaft to the driven shaft is a separate item in the HEIDENHAIN range.

Lifecycle

The ROD 450 is discontinued. The successor path is reported inconsistently in the available sources: one vendor page lists the ROD 420 as the successor while its own body text states the ROD 450 was “replaced by the ROD 480 with an in-line signal adapter”. The ROD 420 is itself also discontinued. The current-generation HEIDENHAIN family for this class of encoder is the ROD 1000 series. For an existing machine with a sinusoidal-input control, an original ROD 450 avoids the interface question entirely, which is the usual reason people look for one rather than specifying new.

Interchange guidance

This item is catalogued and searched under a wide spread of formats. All of the following refer to the same encoder: ROD 450, ROD-450, ROD450, ROD 450-2540, ROD-450-2540, ROD4502540, 251568-1N, 251 568-1N, 251-568-1N, and ID 251568. When cross-referencing against a machine parts list, match on the full ID with suffix where you can, and on line count plus signal type where you cannot.