> AI Summary
- Modern PLCs read manipulator position through incremental or absolute encoders, with SSI, EnDat 2.1 (up to 21-bit) and BiSS C as the dominant 2026 protocols.
- Absolute single-turn and multi-turn encoders eliminate homing routines and reduce cycle time on pick-and-place and gantry lines.
- Encoder selection now hinges on functional safety (SIL 2/3) and IIoT-level diagnostic data, not just pulse count.
- Allen-Bradley, Siemens, Mitsubishi, Omron and Fanuc PLCs all support these protocols via dedicated high-speed counter or technology modules.
- KOEED keeps both new and legacy encoder and counter modules in stock — send your BOM to Moritta@KOEED.COM for a quote within 24 hours.
PLC position detection in 2026 is dominated by absolute encoders on SSI, EnDat 21-bit and BiSS protocols, replacing legacy incremental setups.
Position detection is the heart of any PLC-controlled manipulator. In 2026 the design conversation has shifted from raw pulse count to safety integrity, edge diagnostics, and absolute feedback over SSI, EnDat 2.1, and BiSS C — driven by IIoT integration and stricter functional-safety expectations on collaborative and heavy-load arms.
Why PLC Position Detection Still Matters in 2026
A manipulator that does not know where its end effector is cannot be trusted to pick, place, weld, or assemble. The PLC remains the controller of record because it scans deterministically, holds the safety program, and drives the HMI. Position detection simply tells the PLC "where am I right now" fast enough to close the loop on every cycle.
Across the nine PLC brands KOEED supplies — Allen-Bradley, Siemens, Mitsubishi, Omron, Fanuc, Schneider, Yaskawa, Panasonic, KEYENCE — every architecture in 2026 still relies on three building blocks: an encoder, a high-speed counter or technology module, and a deterministic scan that closes the loop. What changed is the wiring, the protocols, and the data that rides alongside the position word.
Encoder Families Used on PLC-Manipulator Lines
| Family |
Output |
Typical Resolution |
Where It Fits |
| Incremental rotary |
HTL / TTL square wave |
Up to 25-bit line count |
Conveyors, low-cost indexing |
| Absolute single-turn |
SSI / EnDat / BiSS |
Up to 21-bit per turn |
Gantry, rotary tables |
| Absolute multi-turn |
SSI / EnDat 2.1 / BiSS C |
Up to 21-bit + 12-bit turns |
Robotic joints, no-homing restart |
| Linear glass / magnetic |
1Vpp / SSI / IO-Link |
1 µm to 100 nm |
Linear axes, machine tools |
What Changed Since 2024
Our 2024 version of this article treated encoders as opaque pulse sources. The 2026 picture looks different on four axes:
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From pulse count to safety. SIL 2 / SIL 3 capable encoders with redundant channels are now common on collaborative and heavy-load manipulators.
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From parallel wiring to serial protocols. SSI, EnDat 2.1, and BiSS C dominate new designs; parallel 24-bit encoders have nearly disappeared outside legacy CNC retrofits.
-
From black box to IIoT node. BiSS C and EnDat 2.2 carry diagnostic data — temperature, vibration, battery health — that the PLC can read alongside the position word.
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From incremental plus homing to absolute multi-turn. Battery-free multi-turn encoders remove homing routines and restart drift on collaborative arms.
> Tip
If your manipulator still homes on every power-up, switching to a 21-bit absolute multi-turn encoder typically saves 8-15 seconds per restart — a real win on lights-out cells running 24/7.
Common Protocols: SSI, EnDat 2.1, BiSS C
| Protocol |
Typical Use |
Cycle / Latency |
PLC Modules |
| SSI |
Classic absolute, RS-422 differential |
100 kHz - 1 MHz clock |
6ES7 138, QJ71C24N, 1756-HSC |
| EnDat 2.1 |
HEIDENHAIN, 21-bit, safety-ready |
8 - 16 MHz clock |
6ES7 138, 1756-EN2T (gateway) |
| BiSS C |
Open standard, IIoT diagnostics |
Up to 10 MHz |
CJ2M-MD21x, FX5-ENET |
Cross-Reference: PLC High-Speed Counter Modules
| PLC Family |
Encoder Module |
Max Frequency |
Notes |
| Allen-Bradley ControlLogix |
1756-HSC |
1 MHz |
Quad encoder, AOI for SSI |
| Siemens S7-1500 |
6ES7 138 (TM PosInput) |
1 MHz |
Native SSI / EnDat 2.1 |
| Mitsubishi MELSEC iQ-R |
RD62P2 |
8 MHz |
High-speed counter, differential |
| Omron CJ2 |
CJ2M-MD21x |
500 kHz |
Built-in pulse I/O, BiSS via gateway |
Wiring & Shielding Tips from the Field
Most encoder faults on manipulator lines are wiring faults, not sensor faults. In 2026 we still see the same three mistakes in brownfield retrofits: shield grounded at both ends, encoder cable routed next to VFD power, and SSI clock set above 1 MHz without proper termination. Use twisted-pair with overall shield, ground one end only at the cabinet, and keep encoder cable at least 200 mm from any VFD output cable run.
Internal Resources
Working on a manipulator retrofit?
Send your BOM to Moritta@KOEED.COM. New modules, EOL encoder cards, and cross-references — all in one quote within 24 hours.
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KOEED Engineering Team
Industrial automation editors at KOEED. We write about PLC sourcing, cross-reference, and legacy system support. Reach the team at Moritta@KOEED.COM.
Frequently asked questions
Should I move from incremental to absolute encoders in 2026?
Yes, if your manipulator re-homes on every power cycle. Absolute multi-turn encoders over SSI, EnDat 2.1, or BiSS C eliminate homing routines and save 8-15 seconds per restart.
Does my existing Allen-Bradley ControlLogix PLC support EnDat 2.1?
Yes via a 1756-HSC counter module plus an EnDat-to-EtherNet/IP gateway. Native EnDat 2.1 input lives on Siemens TM PosInput (6ES7 138) and on newer Mitsubishi MELSEC iQ-R modules.
SSI vs EnDat vs BiSS — which protocol should I pick for a new line?
SSI is the lowest-cost absolute option. EnDat 2.1 fits safety-critical HEIDENHAIN ecosystems. BiSS C is the best choice for open-standard, IIoT-style diagnostics across vendors.
Can I still buy legacy 24 V incremental encoder modules?
Yes. KOEED stocks both current and legacy encoder and counter cards from Allen-Bradley, Siemens, Mitsubishi, and Omron. Send your BOM to Moritta@KOEED.COM for a quote within 24 hours.
What is the biggest wiring mistake on SSI / EnDat lines?
Grounding the cable shield at both ends and routing encoder cable next to VFD power. Ground one end only at the cabinet, and keep at least 200 mm clearance from any VFD cable run.
