A correct rotary encoder line on a robotic workcell RFQ names the output type, PPR or bit resolution, shaft mounting, supply voltage, and interface protocol in that order, with hazardous-area and ingress fields called out only when the cell demands them [S1][S2].
Industrial cells typically fit into two camps: incremental encoders (cheaper, pulse-based, need a homing routine at every power-up) and absolute encoders (parallel or bus-output, retain position through power loss) [S2]. A 25 mm incremental unit such as the OMRON E6A2-C family runs on 5 VDC -5% to 12 V +10% or 12 VDC -10% to 24 VDC +15% with ripple p-p 5% max, illustrating the kind of tolerance bands buyers should pin on the RFQ [S6].
Output Type and Resolution: Incremental vs Absolute
Incremental encoders output a square-wave A/B pair with the phase difference held at 1/4 pitch; counting pulses gives angle, and direction comes from the A vs B timing [S2]. A 4x multiplier circuit differentiates the rise and fall of both phases, quadrupling electrical resolution from a single disk pattern, which is why the same mechanical PPR can be quoted four different ways on a vendor quote [S2].
Absolute encoders output the angle as a digital code, so position survives power cycling and no homing return is needed at startup [S2]. The Pepperl+Fuchs AHM58-H multiturn absolute encoder packages 30 bit multiturn resolution in a 58 mm industrial housing with up to 4096 pulses on the incremental track and an optically isolated RS-422 interface at up to 2 MBaud [S4]. Spec it on the RFQ when the cell must resume mid-program after an e-stop or a brown-out; spec incremental when the controller handles homing on every boot and cost per axis matters.
PPR, Bit Count, and What the Controller Sees
PPR (pulses per revolution) for incremental units commonly runs from a few dozen to a few thousand PPR, with optical disks delivering the upper end of that range [S7]. The NEMICON selection table splits its incremental line into Low Pulse and Standard Models, with supply rails of DC 4.5-30 V on the wide-tolerance parts and 4.5-5.5 V on the precision low-pulse models [S8].
For absolute encoders, the comparable number is single-turn or multiturn bit depth rather than PPR; the AHM58-H at 30 bit multiturn gives 2^30 distinguishable positions across the full revolution count, which a buyer should write on the RFQ as "30 bit multiturn, optical, RS-422" rather than leaving the controller's counting math as an open item [S4]. Spec the disk technology (optical vs magnetic) only when the application demands it; OMRON's incremental families E6A2-C through E6H-C are all optical disk designs, while the magnetic hobby-grade AS5048B sits at 14 bit and is typical of low-cost MCU boards, not industrial cells [S2][S10].
Mechanical Mounting: Shaft, Hollow, and the Coupling Question
Shaft style is the single mechanical decision that drives housing choice: solid shaft, hollow shaft, or built-in/stub variants. The AHM58-H ships as a hollow-shaft unit in a 58 mm housing, which is the standard industrial footprint for direct mount on a motor or gearbox rear face [S4]. NEMICON splits its catalog into Shaft Encoder, Hollow Shaft Encoder, Built-in Encoder, Modular Encoder, and Manual Pulse Generator series, with Heavy Duty, Standard, and Low Pulse models inside the shaft line [S8].
For a robotic workcell, write the RFQ with shaft diameter, shaft length, and mounting style (clamp, synchro, or through-hollow with torque arm) as separate fields. A solid-shaft encoder typically mates to the load through a flexible coupling, which adds compliance to the drivetrain; hollow-shaft units mount directly on the motor shaft and need a torque arm to resist reaction forces. Omitting the torque-arm requirement when specifying a hollow-shaft encoder is one of the classic requote triggers, because the vendor has to assume the worst-case bracket design.
Electrical Interface: Push-Pull, Line Driver, and Fieldbus
Incremental encoders on industrial cells are usually quoted with a push-pull (voltage) output or a line-driver (differential RS-422) output. Differential outputs reject common-mode noise on long cable runs to the controller, which is why an RS-422 interface is standard on multiturn absolute encoders such as the AHM58-H [S4]. Single-ended push-pull outputs are fine for short cable runs inside a control cabinet but become a noise risk once the cable leaves the cabinet and runs alongside drive power.
For absolute encoders in a robotic workcell, the fieldbus choices are typically SSI, PROFIBUS, PROFINET, EtherCAT, or RS-422, and the AHM58-H covers the RS-422 case at 2 MBaud [S4]. Pepperl+Fuchs also sells rotary encoders for hazardous-area applications where Ethernet-APL and SIL-rated I/O are needed; the same vendor catalogs AS-Interface, IO-Link, and PROFIBUS PA gateway options that an absolute encoder can be ordered against [S9]. Buyers specifying a cell that already runs an EtherCAT motion bus should write "EtherCAT interface, 30 bit multiturn" on the RFQ line rather than leaving the protocol open; the protocol choice is the second-largest cost driver after the resolution.
Environmental, Safety, and the Standards You Pin
Ingress protection, shaft load rating, vibration, and operating temperature are the four environmental fields that should appear as separate line items on a workcell encoder RFQ. Industrial 58 mm absolute housings such as the AHM58-H are typically specced to IP65 or IP67 on the shaft side; if the cell is washdown (food, pharma, outdoor), pin IP67 or IP69K and write it on the line [S4].
Where the cell sits in a hazardous area, the encoder line should reference ATEX/IECEx categories, and the buyer can align it with the cell's wider fieldbus gateway spec (see Fieldbus gateway certification checklist for harsh factory floor). Pepperl+Fuchs catalogs explosion-protected encoders under its "Sensors for Hazardous Areas" segment alongside the same vendor's surge protection barriers and remote I/O systems, so the certification regime (Ex d, Ex e, Ex i) can be specified on the same RFQ block as the encoder [S9].
RFQ Spec Line: Putting It On Paper
A clean encoder line for a 6-axis robotic workcell reads: "Incremental rotary encoder, 5000 PPR, 4x evaluation, RS-422 line driver, 24 VDC ±10%, IP67, hollow shaft 10 mm, M12 connector, operating temperature 0 to +60 °C, CE/UL, 2 m cable included." Substitute "absolute" and "30 bit multiturn" if the cell needs position retention through power loss, and add "EtherCAT" or "PROFINET IRT" to the interface field if the motion bus is already fixed [S1][S2][S4].
Common spec gaps that cause requote cycles: leaving Z/index pulse as "optional" (it is required for home-position verification on most cells); leaving the connector type open (M12 vs M23 vs cable gland); leaving the shaft diameter as "standard" (10 mm, 12 mm, and 15 mm are not interchangeable on the same bracket); and leaving the supply voltage as a range (24 VDC is not the same tolerance as 5-30 VDC). Pulling the same fields into a line-by-line spec table also helps the buyer reuse it for adjacent subsystems, the same discipline used in How to Specify a Remote I/O Module on an MCC RFQ and the broader Embedded part selection for industrial facilities: 2026 spec map. Trackable next signals: the controller's encoder input card (differential vs single-ended, max input frequency in kHz) and the cable length from the cell panel to the controller, both of which the vendor will need before the encoder quote is final [S1][S4].
For the relevant spec sheets and selection criteria, see linear encoder, and rotary hammer.