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Multimode Encoder Signal Filters Overview
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The encoder (or pulse generator), in rotary or linear form, is the most popular motion/position sensor and these filters complement, safeguard, maintain and extend their capabilities and performance.
Terminator Multimode Encoder filter
Terminator multimode encoder signal filter
Mini Multimode Encoder filter
Mini multimode encoder signal filter

The filters remove all types of electrical noise (common and differential mode, dV/dt transients, ground loop generated etc.) in the encoder signal lines as well as the corrupting effects of mechanical noise and vibration (phantom movement, dither etc.). They reconstruct the encoder signals to reflect the correct encoder position and speed signaling. Performance is safeguarded and problems such as:

are eliminated. (The subject is treated extensively and in detail in our paper Eliminating Phantom Movement in Encoder Applications).  See also the Frequently Asked Questions page.

In addition to the above, our specialty multimode frequency averaging filters process the encoder signals to reproduce them at average input frequency in speed/velocity control applications.

Our multimode filters are offered in two standard lines: the fully featured Terminator line and the low cost Mini line which addresses less demanding applications. Both are all-in-one, comprehensive products, each device addressing all and any combination of known encoder application issues.  Both types process digital quadrature encoder signals with the following features and characteristics:

Multimode Encoder Filter Model Line-up and Features Overview
Feature EFxO Multimode Encoder filter
Terminator line
Mini Multimode Encoder filter
Mini line
Galvanically isolated input and output stages to interrupt unavoidable system ground loops eliminating related noise as well as protecting the input stage of the driven controller from high voltage transients. 5 V/ns minimum dV/dt galvanic barrier immunity 0.1 V/ns minimum dV/dt galvanic barrier immunity
Four selectable modes of digital processing:
  • Unfiltered: the outputs are buffered replicas of the inputs,
  • Filtered: the encoder inputs are processed for electronic noise only,
  • Recovered x1: the encoder inputs are processed for electronic noise and analyzed for mechanical position to recover corrupted motion sequences. The outputs are in quadrature format and the mark (or index) channel is processed for electrical noise.
  • Recovered x4: Same as the Recovered x1 mode, but with output resolution quadrupling. The output signals are a clock/direction or an up/down pair at four times the input frequency instead of the quadrature format.
Yes Yes
Test mode. Depending on the chosen mode the filter outputs simulate the function of a 1024 ppr encoder Output frequency is 1/64 the chosen sampling frequency Output frequency is fixed
Direction reversal. One of the encoder channels can be complemented to effect a direction reversal, thus saving the rewiring/reconnection of the encoder signals. Yes Yes
Supply, signal and worn/faulty encoder indication. Five LEDs indicate the status of the power supply, the three encoder channels and the presence of out-of-sequence signalling, typically caused by a worn or faulty encoder. Yes Yes
DIP switch selectable options. All operational parameters and functions are set/reset via DIP switches. Yes Yes
Selectable sampling frequency. The encoder signals are DSP processed at selectable frequencies to interface to slower equipment or tune out problem noise sources in particularly difficult applications. Yes No
Types of EIA(RS)422 input termination Standard DC, AC and none Standard DC and none
Power supply Internal dual voltage 115/230 VAC twin isolated supply. The twin supply powers the two internally isolated, input and output, filter sections and can also power the monitored encoder with regulated 5 VDC or unregulated 10/15 VDC None. Power must be supplied externally to each of the two filter sections.
Enclosure Cast aluminum enclosure of IP65 protection and high noise immunity. Plastic, DIN rail mountable, IP40 protected.
Available speed grades (table below) High, Standard and Low Basic only

The above all-in-one, multimode approach is justified when considering that in practical applications there is typically more than one mechanism at play eroding encoder performance at any time (see our paper on this or the encoder filter FAQ page). This makes a multimode filter the only effective, efficient, viable and conclusive solution to encoder noise problems.

The filters are characterized by their speed grade specifying the maximum quadrature input frequency which can be processed.  The limit is different for each filter mode:

Maximum Quadrature Input Frequency Capability per Filtering Mode
Speed Grade Unfiltered Filtered Recovered x1 Recovered x4
Basic 300 kHz 125 kHz 100 kHz 31.3 kHz
Low 300 kHz 250 kHz 200 kHz 62.5 kHz
Standard 10 MHz 1.5 MHz 1.2 MHz 375 kHz
High 10 MHz 3.0 MHz 2.4 MHz 1.5 MHz

The filter design is characterized by typical industrial application considerations: low ownership cost, standard interfacing, fool-proof installation, transparent operation, results-oriented and all-inclusive design. The filters feature the following operational characteristics:

You can buy small quantities of the Terminator and Mini filters online here.
Terminator OEM Encoder Filter
The technology is also available
in custom versions for OEMs.

Download PDF leaflet or request further information or a quote/offer

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