The short version: Hengstler discontinued the E9, M9 and PC9/PC9S encoder series, with final orders taken on 2 August 2024, and the manufacturer states there is no direct replacement. Cross-referencing these units means matching five parameters by hand, because no part number maps one to one. Read the encoder label, then the original datasheet, then choose a current family.
Hengstler's notice, issued through Dynapar, gives supply constraints and limited demand as the reason, then adds the sentence that matters for anyone rebuilding a bill of materials: there is no direct replacement to order.
What was retired, and what it was
The official Hengstler catalogue files the E9 and M9 under motor feedback systems for miniature DC and stepper motors, and the PC9/PC9S under economy incremental encoders. All three were small, low-resolution, single-ended devices filling roles that larger or smarter hardware covers today.
E9. Pulses ran 100, 144, 200, 256, 300, 360, 500 and 512 ppr. Hub shaft sizes were 1.5, 2.0, 2.5 and 3.0 mm, plus 0.125 in and 0.156 in. Installing one required a dedicated mounting kit, MK E9, specific to the hub shaft diameter. The connection was a 10-pole header on a 30 cm ribbon cable.
M9. Total length under 15 mm, mass 4.14 g, moment of inertia 0.11 gcm². Resolution reached 512 lines per revolution, operating frequency 200 kHz, and the operating range ran from −40 to +100 °C. Hollow shaft options were 1.5, 2.0, 2.5, 3.0 and 4.0 mm, and the mating shaft had to measure between 9.75 mm and 11.1 mm. Output was single-ended quadrature A and B with an index pulse. The catalogue notes that the M9 could replace most Hewlett Packard HEDS-5XXX encoders, which tells you what class of motor it lived on.
PC9 and PC9S. Pulses from 100 to 512. Outer diameter 22 mm, or 22.86 mm for the imperial version. Shaft 1/8 in (3.2 mm) or 1/4 in (6.4 mm). Supply was DC 5 V ±10 %, drawing 10 mA typical, with standby current of at most 50 µA on the PC9. Output levels were 2.5 V minimum high and 0.5 V maximum low, at 3 mA for the PC9 and 6 mA for the PC9S at 25 °C. Maximum pulse frequency 200 kHz, operating range −40 to +100 °C, and a 10-pole header on the PC9 against a 5-pole header on the PC9S.
Note what the PC9 entry lacks: any ingress protection class. A 22 mm encoder with no stated IP rating was never meant for a washdown line.
Three reasons nothing drops straight in
The mechanical envelope comes first. The M9 is under 15 mm long and weighs 4.14 g. Current industrial encoders in the 58 mm class are measured in hundreds of grams, and no amount of bracket work puts one inside the space an M9 occupied. Where the M9 was mounted directly on a miniature motor, the replacement question is really a question about the motor.
The interface comes second. All three retired series used single-ended quadrature at 5 V logic. Current families offer push-pull, RS422, or absolute serial interfaces such as SSI and BiSS with a 1 Vpp sine track. Moving to an absolute interface changes what the drive expects, so the encoder and the controller settings have to be settled together rather than one at a time.
The accessory comes third. The E9 depended on a mounting kit made for the E9, so budget for a new mounting plate on any replacement.
Cross-reference table
Every figure below is taken from Hengstler catalogue entries. Where a difference is a downgrade, it is marked as one.
Which current family to specify
Work through these in order. The first one that matches your machine normally ends the discussion.
- If the failed unit sat on a servo or stepper motor and you need position after a power cycle, use an absolute motor-feedback encoder. ACURO AD36 is built for brushless servomotors, installs where a resolver size 15 would, uses an 8 mm through hollow shaft, and reaches 22 bits single-turn plus 12 bits multi-turn over SSI or BiSS. It is 37.5 mm across and rated IP40, so it belongs inside a motor or a sealed enclosure rather than on an exposed shaft.
- If it sat on a machine shaft and you need speed or incremental position, use ICURO RI58-O. It is the general-purpose option: up to 10,000 lines and 40,000 steps, protection up to IP67, push-pull or RS422, and shafts from 6 mm to 15 mm in hub, solid and through hollow versions. For hotter machinery, the RI58-T variant extends the operating range to 100 °C.
- If the machine gets washed down or the shaft is large, use HSD25 or ISD25. Hollow shaft from 6 mm to 19 mm, 1 to 3,600 pulses, IP67 with NEMA 4X and 6 options, −40 to +100 °C, and a housing available in stainless steel or nickel. ISD25 adds ATEX certification for intrinsically safe installations.
- If the location is classified, go to RX70 or RX71, the series Hengstler names for EX applications in its own RI58 documentation.
- If it was a PC9 or PC9S on a small machine and cost matters more than size, use ICURO RI32-O and solve the mounting. It is the closest current economy incremental unit, but you are moving from a 22 mm body to a 30 mm body, from a 5 V single-ended output to push-pull, and from −40 to +100 °C down to −10 to +60 °C. That last change is the one buyers miss.
What to send with a cross-reference request
Five items decide the answer.
- The complete part number from the label, including everything after the dot. The suffix carries shaft, flange, connection and output coding. A shortened number produces a shortened answer.
- Resolution in pulses per revolution, or the drive's scaling requirement if the original figure is lost.
- Shaft type and diameter, plus the flange or bolt pattern. Measure the hardware instead of trusting the drawing.
- Output interface and logic level. Single-ended 5 V, push-pull, RS422 and absolute protocols are not interchangeable.
- Environment: ambient temperature, required IP rating, shaft load, and whether the area is classified.
Attach the original datasheet if you still have it. When the label is worn, a clear photograph of it usually works.
Sourcing the replacement
QINUO supplies genuine, brand-new Hengstler encoders, counters and safety relays from its Hong Kong operation, alongside the rest of its industrial range. We do not hold a factory appointment for every line, and any supplier waving such a claim without documents deserves the same scrutiny. What we can do is read your old part number, put it against the current Hengstler catalogue, and quote the closest current family with the interface and mounting differences written down rather than left for you to discover at commissioning.
Start from the brand directory or the Hengstler brand page to see the series we carry. Three useful starting points are ICURO RI32-O/1500ER.11KB-D0 for economy incremental work, ICURO RI58-O/10000ES.41KA-F0 for general-purpose machine shafts, and ACURO AD36/1222AF.0RBV2 for absolute motor feedback. The full product catalogue covers the wider range, and our application cases show this hardware working on packaging, material handling and machine-tool projects. Send the label details through the contact page and an engineer will read the part number before anyone quotes a price.
FAQ
Does Hengstler offer a direct replacement for the E9, M9 or PC9/PC9S?
No. The discontinuation notice states that Hengstler does not offer a direct replacement for any of the three series and refers customers to a Hengstler account manager for alternatives. Any listing claiming a like-for-like successor part number should be treated as something to verify rather than accept.
Can I use another brand's encoder to replace a discontinued Hengstler unit?
Yes, provided the parameters match. Encoders are not brand-locked, and a drive only sees pulses, direction and an index. What breaks is the fit: shaft, flange, output type, logic level, resolution and environment. Match all six and the substitution works. Miss one, usually the output level, and it will not.
What replaced the Hengstler M9 encoder?
Nothing directly. The M9 was a motor-feedback encoder under 15 mm long and weighing 4.14 g, and no current Hengstler encoder matches that envelope. If the motor has space, an absolute motor-feedback unit such as ACURO AD36 brings a modern digital interface. If it does not, the realistic options are re-mechanising the axis or moving to a motor with an integrated encoder.
Is the RI58 series discontinued?
No. ICURO RI58 is a current Hengstler family, listed with hub shaft, solid shaft and through hollow shaft versions, diameters from 6 mm to 15 mm, protection up to IP67, and push-pull, push-pull complementary or RS422 interfaces. For most general-purpose incremental replacements it is the sensible destination rather than a compromise.
How do I check that a quoted encoder is genuinely the right part?
Ask for the full part number with every suffix code written out, then check it against the Hengstler catalogue or configurator instead of a distributor's shortened listing. After that, confirm shaft, flange, output, supply voltage and temperature range one by one against your original datasheet. Five minutes of comparison is cheaper than a commissioning day lost to a mismatched output level.
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