Magnetic rotary encoder
Renishaw RLS AksIM-4 magnetic rotary encoder
Off-axis absolute magnetic ring encoder for through-hole rotary axes, including large-diameter rings. Non-contact with optional self-calibration.
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What are you specifying?
Select everything you need. A motor, drive and gearbox can be specified together as one axis.
Key specifications
| Outer diameter | 53–150 mm |
|---|---|
| Resolution (max) | 21 bit |
| Interface | BiSS C |
Summarised in our own words from Renishaw plc's published data; series maxima, individual models vary. Last checked 2026-10-29. Source 1 · Source 2 · Source 3 · Source 4
Notes on this data
Presented on renishaw.com magnetic encoders page as an RLS product; figures from rls.si. Big-ring version 115/150 mm OD, 20/21 bit; HIPERFACE DSL version 53/80 mm OD, up to 20 bit, accuracy up to ±0.005°; dual concentric version 19+19 bit. Operating -40 to +105 °C. Supply 4.5-5.5 V.
Specify Motion is not affiliated with Renishaw plc. Renishaw and RLS AksIM-4 are used only to identify the product. Comparisons use published figures; always confirm against the current datasheet.
Renishaw RLS AksIM-4 replacement and alternative options
Use these supply-network options as a starting point for an engineering check. We can also help source the original Renishaw part. Published series figures do not establish an exact-model or drop-in replacement: confirm ratings, fit, interfaces and approvals for your application.
Highest-resolution Bogen absolute head, 21 to 24 bit, for linear and rotary scales.
| Published maximum | RLS AksIM-4 | AKS17 |
|---|---|---|
| Resolution | 21 bit | 24 bit meets or exceeds |
Compact incremental head with wide -40 to +125 C range; IKP11 is the open IP00 version. Works on linear and rotary scales.
Incremental magnetic head with analogue sin/cos output. Works on linear and rotary scales.
Figures are the highest published for each series and are not always measured the same way. A higher figure is not automatically a better choice: mounting, duty cycle, feedback, connectors and approvals matter too. An engineer will check the fit against your application before recommending anything.
Typical applications
What a magnetic rotary encoder is
A magnetic rotary encoder measures angle by sensing the field of a magnet with Hall-effect or magnetoresistive sensors. On-axis designs place a diametrically magnetised magnet on the shaft end above a sensor chip; off-axis designs read a multi-pole magnetic ring around a hollow shaft. Signal processing turns the field into absolute or incremental position. Because there is no optical path, magnetic encoders tolerate dust, oil, moisture and vibration, typically with moderate resolution and accuracy at low cost.
When engineers choose a magnetic rotary encoder
Choose a magnetic rotary encoder for robust, compact feedback in harsh or cost-sensitive applications, such as motors, AGVs, robotics, agricultural and mobile machinery. Off-axis rings suit hollow joints. The trade-offs are accuracy and magnetic interference: accuracy is typically lower than optical, and strong stray fields from brakes or motors can affect the reading. For high precision, choose optical. Consider shielding and mounting tolerances carefully.
How to specify the Renishaw RLS AksIM-4
Send these with your enquiry and an engineer can confirm the right RLS AksIM-4 variant or an equivalent:
- Resolution (bits or counts)
- Accuracy (degrees or arcmin)
- Absolute or incremental output
- On-axis or off-axis ring mounting
- Interface: SSI, BiSS, SPI, PWM or analogue
- Mounting tolerances: gap and runout (mm)
- Environment and IP code
Common mistakes to avoid
- Mounting near brakes or motor magnets without shielding
- Exceeding the allowed air gap or runout
- Expecting optical accuracy from a magnetic encoder
- Overlooking calibration after installation
Renishaw RLS AksIM-4: frequently asked questions
Can you help replace Renishaw RLS AksIM-4 or source the original?
Send the full model code, quantity and required date. Our engineers can check original-part availability and assess suitable alternatives, including supply-network options where appropriate. We confirm compatibility and any changes needed before recommending a replacement.
What is the Renishaw RLS AksIM-4?
Off-axis absolute magnetic ring encoder for through-hole rotary axes, including large-diameter rings. Non-contact with optional self-calibration. Published series figures include outer diameter 53 mm, outer diameter 150 mm, resolution 21 bit. It is made by Renishaw plc; Specify Motion can help source it or propose an equivalent.
Who makes the Renishaw RLS AksIM-4?
The Renishaw RLS AksIM-4 is made by Renishaw (Renishaw plc) and is listed here for engineers comparing options. Specify Motion is not affiliated with Renishaw plc; brand names are used only to identify the product.
What is the outer diameter of the Renishaw RLS AksIM-4?
The published series minimum outer diameter is 53 mm. Individual models and sizes in the RLS AksIM-4 range vary, so check the exact variant against your duty cycle, mounting and environment, or ask our engineers to confirm the right size for you.
Is there an alternative to the Renishaw RLS AksIM-4?
We can assess suitable replacement options. On published figures, Bogen AKS17 and Bogen IKS11 / IKP11 are options to assess from our supply network. An engineer confirms the fit against your application before recommending anything.
Are magnetic encoders as accurate as optical encoders?
Typically not. Magnetic encoders tolerate contamination and vibration well but usually have lower accuracy and resolution than optical encoders of similar size. Self-calibration and good mounting can improve results. For high-precision positioning and metrology, optical encoders remain the usual choice, while magnetic types win on robustness and cost.
What is the difference between on-axis and off-axis magnetic encoders?
On-axis encoders read a single magnet on the end of a shaft, which is simple and compact. Off-axis encoders read a magnetic ring around a shaft, which leaves the centre free for hollow shafts or cables. Off-axis designs are more sensitive to mounting tolerances.
Further reading: Magnetic vs capacitive vs optical encoders · How to select an encoder · Encoders and feedback
Other magnetic rotary encoder series
Engineer support
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