Specifications

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When deciding whether or not a modular or bearing encoder is the best solution for your application, consider these factors:
1. First and foremost, shaft end float and TIR must be within the encoder’s specifications. This is so important that if you don’t have (or
can’t get) this information, or don’t trust what you have, then an encoder with bearings is strongly recommended, since it will be a much
safer choice.
2. Modular encoders can be a good choice for high-speed applications, those above 10,000 RPM, because there are no speed limitations
dictated by encoder bearings. For example, EPC’s Accu-Coder Model 121 Modular Encoder has been successfully operated at speeds in
excess of 40,000 RPM. The speed limiting factor is the maximum frequency of the encoder, which is a function of disk resolution, RPM’s
and the signal processing circuitry. Most encoder manufacturers include maximum frequency in product specifications.
3. If the motor is to be used under considerable mechanical load, where the motor bearings could experience extra wear, then an
encoder with bearings would be the better choice. Remember, the bearings of the host device, serve as the bearings of the modular
encoder.
4. Modular encoders are difficult to seal. If your application requires wash-down, or if the operating environment is dirty, dusty or wet,
then an encoder with bearings and seals should be your first consideration. Such environments effectively rule out modular encoders,
unless external protection, such as an IP sealed motor cover, is used.
5. If your application requirements combine high maximum frequency (> 200kHz), high temperature (100C or higher), and higher
resolution (>2048 CPR), then an encoder with bearings is recommended. For long term reliability, this combination of factors requires
the air-gap between the disk and sensor to be very narrow and tightly controlled. An encoder with bearings simply provides a more
stable optical platform.
6. Lower resolutions (up to 1024 CPR) are more forgiving of End Float and TIR, and are often well-suited for modular applications if the
operating environment is appropriate.
7. If you plan to use numerous encoders, then the relatively lower price of a modular encoder could save you some money. On the other
hand, the greater durability and easier installation of an encoder with bearings might be worth a slightly higher unit price. In any case,
carefully weigh the factors of long term support costs versus lower acquisition costs before making your final decision.
Quick Selection Chart
Parameter Attribute Use Modular Use Encoder with
Bearings
Motor shaft end oat and TIR Within the encoder manufacturer’s specications Yes Yes
Motor shaft end oat and TIR Outside the encoder manufacturer’s specications No Yes
Motor shaft end oat and TIR Don’t have the information or don’t trust Not suggested Suggested
High-speed applications Above 10,000 RPM Good possibility Not suggested
Severe duty application Motor bearings have extra load and wear Not suggested Suggested
Dirty environment May need seals Not suggested Suggested
Combination of high frequency
response, temperature, CPR
>200kHz, >100°C, >2048 CPR Not suggested Suggested
Lower resolution requirement <1024 cycles per revolution Good possibility Good
Number of units needed Acquisition cost vs. life cycle cost Consider if large
volume
Good
enCoder seleCTion
ConsideraTions
5
Modular vs. Bearing Encoders