ABB FEN-21 Resolver Interface Module

A resolver interface for servo and motion drives

The FEN-21 is ABB’s Resolver Interface, an option module for compatible ABB drives that reads a motor resolver and returns rotor position and speed to the drive. ABB’s manual 3AFE68784859 Rev E describes it as an interface for one resolver with PTC or KTY support, a TTL encoder connection, a TTL encoder emulation output and two digital inputs for position latching. A resolver is a rugged analogue sensor fed by an excitation signal, which is why it is often preferred on motors exposed to heat, dust or vibration.

Technical specifications

How the FEN-21 handles a resolver

The resolver input X52 supplies the excitation signal on the EXCITATION+ and EXCITATION- terminals at 4 to 12 Vrms and 100 mA at most, and receives the sine and cosine signals as differential inputs of 2 to 7 Vrms. The same connector carries the PTC or KTY motor thermistor. Position and speed resolution are both 24 bits, and the resolver cable may be up to 100 m long, the longest cable allowance among the FEN encoder modules. The amplitude and frequency of the excitation signal are matched to the resolver in the drive parameters, as the manual describes.

Other connections and installation

A TTL encoder can still be connected to X51, with 5.5 V at 180 mA and 24 V at 150 mA, cable limits of 30 m, 60 m or 100 m depending on encoder voltage, and 500 kHz RS-422/485 signals. The TTL emulation output X53 repeats the measured position for another controller, and the latch inputs X54 capture position at an external event. A jumper X301 selects the encoder supply voltage. The module draws 350 mA at 24 V, with at most 5 W for encoders, latches and cabling, is rated IP20 and inherits the ambient limits of the drive. Typical applications are servo-style positioning axes, machine tools, cranes and packaging lines where a resolver survives heat and shock better than an optical encoder; select the module by the sensor type on the motor, not by power rating.

Datasheet and quotation

Values come from the linked ABB user’s manual for the FEN-21 and ABB’s own product page. Seven Star LLC quotes the FEN-21 from Muscat; send the drive type designation so that compatibility with the option slot and firmware can be checked. Confirm before ordering that the drive, control unit and firmware support this module, and note that older manuals may predate current drive generations. More encoder interfaces are in Encoders, and the FPBA-01 PROFIBUS adapter page covers a different kind of option module.

How the FEN-21 Resolver Interface Works

A resolver is a small rotary transformer mounted on the motor shaft. The FEN-21 feeds its primary winding with an AC excitation signal, adjustable from 4 to 12 Vrms and from 1 to 20 kHz, and the two secondary windings return sine and cosine signals whose amplitudes change with the rotor angle. The module demodulates these two signals and calculates the absolute angle within one revolution; by following the angle over time it also calculates speed. Because the resolver has no electronics or optical parts, it tolerates heat, vibration and contamination far better than most encoders.

The drive uses this position and speed feedback for closed-loop motor control. The FEN-21 can also repeat the position as a TTL pulse train on its emulation output for another drive or controller, and its latch inputs capture the exact position when an external signal arrives, for example from a registration sensor.

Technical Details from the ABB FEN-21 Manual

• Resolver excitation: 4–12 Vrms, 1–20 kHz, 100 mA maximum; sine/cosine inputs 2–7 Vrms.
• TTL encoder input: 1–65535 pulses per revolution with reference mark; jumper X301 selects +5.5 V or +24 V encoder supply, and should be removed when an external supply or another FEN’s emulation output is connected.
• TTL speed resolution 0.004 rpm, position resolution 16.8 million counts per revolution, speed range ±32768 rpm.
• Module size about 31 × 106 × 63 mm.
• Two LEDs: STATUS (green OK, orange not initialised or communication fault) and ENC ST (green OK, red fault on X51, orange fault on X52; flashing indicates a warning).

Installation & Maintenance of the FEN-21

• Switch off the drive and wait 5 minutes for the DC capacitors to discharge before fitting the module.
• Fit the FEN-21 into a free option slot with the plastic clips and locking tab, then tighten the fixing screw: the screw earths the cable shields and connects the module ground.
• Use shielded twisted-pair cable; a resolver cable needs four twisted pairs. Tighten the plugs to 0.3 Nm and do not run encoder cables parallel to motor cables.
• A motor thermistor connected to the module needs double or reinforced insulation from the motor windings.
• Wire the phasing correctly: the encoder channel that leads when the motor turns forward goes to input A.
• Set the module up through the drive parameters described in the drive firmware manual, and confirm the excitation settings match the resolver data.

Selection & Typical Applications in Oman & the GCC

The FEN-21 is chosen when the motor is fitted with a resolver; motors with TTL or absolute encoders use other FEN modules. Check the drive’s ordering information or hardware manual to confirm that it supports the FEN-21. Typical uses include positioning axes, cranes, test benches and machines in hot or dusty plants in the region, where resolvers survive conditions that would damage optical encoders.

Why Source from Seven Star LLC

Seven Star LLC is an independent supplier in Muscat. Seven Star LLC supplies ABB drive option modules across Oman and the GCC. Send the FEN-21 code and the drive type designation and request a quote; our team can help confirm the correct ordering code.