ABB FEN-31 HTL Encoder Interface Module for ABB Drives

ABB FEN-31 HTL encoder interface module

The ABB FEN-31 is a plug-in encoder interface for ABB drives that read HTL (high-threshold logic) pulse encoders. It feeds speed and position back to the drive for closed-loop control and also offers a TTL emulation output so another device can share the encoder pulses.

Typical uses are hoists, winders and conveyors where the drive needs accurate speed from an incremental encoder.

Before ordering, check the encoder datasheet for its output type and signal level. An HTL encoder swings between roughly the supply voltage and zero, which is why a dedicated HTL interface is used instead of a TTL one. The module can also pass the signal on through its TTL output, which saves a second encoder on shared shafts.

Technical specifications

Encoder wiring limits

The module supports differential and single-ended push-pull encoders, open collector and open emitter outputs. Maximum cable lengths depend on the type: 300 m for differential, 200 m for single-ended and 100 m for open collector or emitter outputs. It supplies the encoder with 15 V or 24 V at 200 mA and processes signals up to 300 kHz.

The TTL output follows RS-422 at 500 kHz and a division of 1 to 65535 pulses per revolution, over a cable of up to 100 m.

Use twisted-pair shielded cable for differential signals, and keep the shield grounded at the drive end. Longer cables reduce the usable frequency, so compare the pulses per revolution and the maximum speed of your machine against the 300 kHz input limit. Speed measurement has 24 bit resolution, and position resolution is 16 million per revolution.

Order code and compatible drives

FEN is ABB’s encoder interface family and 31 is the HTL version. On an ACS880-01 the module is option +L502, for instance on the ACS880-01 drives. The manual also names the ACS850 and ACSM1.

Do not confuse it with TTL or resolver modules of the same family; check the encoder signal level first. Other drive accessories sit in the encoders category.

An option module is only useful when it matches both the drive and the network, so send us the drive type code, its firmware level and the controller that will talk to it. Add the required cable length and connector type. With those facts the right module can be confirmed, and the manual attached here helps your engineer check the parameters.

When closed-loop encoder feedback is needed

Many drive applications run well in open-loop or sensorless control, but some machines need a measured speed or position from the motor shaft. Hoists and cranes require reliable torque at low and zero speed, winders and unwinders need accurate speed to hold web tension, and conveyors in synchronised lines may need precise speed matching between sections. In these cases an incremental encoder on the motor or machine shaft, connected through the FEN-31, gives the drive the feedback it needs for closed-loop control. Decide at the design stage whether encoder feedback is truly needed, because it adds an encoder, cable and commissioning work to the installation.

Matching the encoder to the FEN-31

The FEN-31 is the HTL member of the FEN family, so the first check is always the encoder output signal level. Then confirm the output type, whether differential push-pull, single-ended push-pull, open collector or open emitter, because the permitted cable length differs between them. Check that the encoder supply voltage selected on the drive side matches the encoder rating and that the encoder current stays within the module supply capability. Finally, compare the encoder pulses per revolution and the maximum machine speed with the input frequency limit of the module.

Using the TTL emulation output

The TTL emulation output repeats the encoder pulses in RS-422 form, with a programmable pulse division. This lets a second device, such as another drive or a controller, receive speed information from the same encoder without mounting a second one on the shaft. Plan the cable route and length for this output separately, and set the pulse division to suit the receiving device.

Commissioning considerations

Install the module in the option slot recommended in the drive manual and wire the encoder according to the terminal assignment in the attached document. Before running closed-loop, rotate the motor slowly and check in the drive parameters that the measured speed has the correct sign and magnitude. A wrong direction or unstable reading usually points to swapped channels or a shielding problem. Only then enable closed-loop control and tune the speed controller. Keep a record of the encoder parameters for future maintenance.

For maintenance, keep the encoder cable shield connections and terminal tightness on the inspection list, since vibration on cranes and conveyors can loosen connections over time. Intermittent speed faults are often traced to cable damage near moving parts, so route the encoder cable carefully, protect it where it passes machine guards or drag chains, and check it whenever the motor or encoder has been removed.

Specifying the FEN-31 in an RFQ

State the type code FEN-31, the quantity and the drive family it will be used with. For ACS880-01 drives, mention option code +L502. Include the encoder make and model if known.

Documents and quotation

The attached ABB manual (3AUA0000031044) lists terminal assignments, parameter settings and fault codes.

Please confirm before ordering: the drive type and firmware, the option slot, the network scanner or PLC and the cable type. Seven Star LLC is an independent supplier in Muscat and confirms current availability and lead time when it quotes.