HeidenhainROD-450-2540Incremental 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:
Read this before anything else on the page. The ROD 450 family outputs 11 µA peak-to-peak sinusoidal current signals. TTL square-wave output is not offered natively on the ROD 450. If your control, counter or drive expects TTL A/B quadrature, this encoder will not drive it directly — you need a HEIDENHAIN EXE interface unit to shape the sinusoidal current into square-wave pulses, or you need a control with a genuine 11 µA sinusoidal input. Plenty of older HEIDENHAIN-era CNCs, position displays and counters have exactly that input, which is precisely the population of machines this encoder belongs to. 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. The downside is that you cannot wire it to a modern digital input card and expect counts.

One honest limit on that: which signal type the specific -1N variant carries is not published. The family output is 11 µA sinusoidal, and the variant suffix is where signal type, connection and cable length are encoded. Verify against your control before committing.

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 450-1000251 568-4F = ROD 450-1800251 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. The mapping of -1N specifically is not published in any HEIDENHAIN variant table we can cite, but the base ID and the sibling pattern establish it clearly enough to order against. If you are sourcing a match for an existing machine, quote the full ID including the suffix — the base ID alone does not specify the encoder you will receive.

Correcting the source data

Two errors in circulation on this part, corrected here.

The brand on this record previously read “HEIDENHAIN ROD”. ROD is the product family designation for HEIDENHAIN’s bearing-mounted incremental rotary encoders, not part of the company name. The manufacturer is HEIDENHAIN; the family is ROD.Some vendor pages quote a “±0.5 µm” accuracy for this encoder. That is a transcription error from a linear-encoder specification — micrometres are not a unit of rotary accuracy. The correct order of magnitude for the ROD 400 family is positioning accuracy quoted around ±13 arcseconds, with system accuracy of 1/20 of the grating period. We are not repeating the micrometre figure.

Published ratings

Type: incremental rotary encoder with integral bearing, separate rotor couplingLine count: 2540 lines per revolution (ROD 450 family range 50 to 5000 lines/rev)Output signal: 11 µA peak-to-peak sinusoidal currentSupply voltage: 5 V ±0.5 VCutoff frequency (−3 dB): 160 kHzShaft: 10 mm diameter solid shaftReference mark: oneProtection class: IP67Maximum mechanical speed: 12,000 rpmOperating temperature: −40 °C to +100 °C
A note on the 2540 figure: 2540 lines per revolution sits comfortably inside the ROD 450 family’s published 50 to 5000 lines/rev range, so it is a valid family build, but no datasheet specific to the 2540-line variant is published. It is stated here as the line count carried by the designation, consistent with the family range, and not as a figure lifted from a variant-specific document.

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 your speed. That is worth working out for your application rather than assuming the 12,000 rpm headline applies: a 2540-line encoder is a resolution choice, and resolution and top speed trade against each other on any incremental encoder.

Mounting, flange and coupling — confirm from the photographs:
The flange type is not published for the ROD 450 specifically. The sibling ROD 456 uses a synchro flange of Ø58 mm with a Ø42 mm bolt circle, and it would be easy to assume the ROD 450 matches — we are not going to make that assumption for you, because a mounting mismatch is an expensive way to find out. Confirm the flange, bolt circle and pilot diameter from the listing photographs against your machine before ordering, and ask if you need a dimension measured.

The same applies to two other configuration items. The ROD 450 was supplied in both cable and flange-socket versions, in radial and axial orientations — the photographs show which this unit is. And because the encoder couples to the driven shaft through a separate rotor coupling, that coupling is a distinct item; whether one is present with this unit is not something the record establishes, so check the photographs and ask before you assume one is included.

Lifecycle, and an honest note on the successor

The ROD 450 is discontinued. The successor path is genuinely unclear in the available sources, and rather than pick the version we like, here is the contradiction as it stands: 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. No HEIDENHAIN migration notice covering the ROD 450 was found. The practical reading: if you are maintaining an existing machine with a sinusoidal-input control, an original ROD 450 avoids the interface question entirely, which is the usual reason people are looking 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.