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Frequently Asked Questions on Multimode Encoder Signal Filters
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The FAQs for our Multimode Encoder Signal Filters are organized into technical and administrative (order processing, shipping etc) sections. The Multimode Frequency Averaging Filter FAQ page is here.

Technical FAQ
1. What does "multimode" refer to and why is such a filter necessary?
2. Why pay more for the multimode approach?
3. What operation/filtering modes do the Terminator and Mini lines offer?
4. What is resolution quadrupling or 4x decoding?
5. Can I use the filter with non-incremental encoders or other non-quadrature signal sources?
6. How can I check that the encoder signals are processed correctly by the filter?
7. How can I check that the receiving controller processes the filter outputs correctly?
8. When was your encoder technology first employed?
9. Which motion control applications need this technology most?
10. What hardware subsystems/features do the Terminator and Mini lines have?
11. Is the filter's operation truly transparent?
12. How can I drive single-ended 5VDC/TTL inputs from the filter's EIA(RS)422 differential outputs?
13. How can I use the x4 clock/direction outputs to drive a quadrature type input stage?
14. How can I check that the encoder works correctly?
15. How can I interface the universal 5 V filter inputs to 8-30 V output encoders?
16. Why use a filter with different input and output types?
17. How does input stage saturation, latch-up or failure arise and how do the Terminator and Mini filters prevent it in encoder applications?
18. How do I determine the filter's maximum quadrature input frequency for my encoder application?
19. Can I use your encoder filters to process resolver noise?

AdministrativeFAQ
1. How can I buy samples for immediate delivery?
2. Can I buy ex-works (I have my own courier/agent)?
3. Is there a minimum order quantity?
4. I would like to promote/market/distribute this technology in my area. What do I do?


Ask a question or clarification

Technical FAQ


1. What does "multimode" refer to and why is such a filter necessary?

"Multimode" refers to the many modes of operation and supporting hardware which the encoder filters have. Our decision to offer the all-in-one solution (and not individual modules) is based on the fact that the encoder signals are nearly always corrupted by more than one cause at any time and so all the available stages are needed for reliable and effective encoder operation (for a discussion on this see this paper).

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2. Why pay more for the multimode approach?

Because encoder signals are affected by many different causes and their symptoms (see our paper on this). These problem sources are always present, each to a different degree and at different times. So, the all-in-one multimode filter is worth the apparent extra expense because it ensures one-stop problem resolution and long term trouble-free operation. The lower cost alternative of addressing a subset of the potential problems by using specific function devices (eg galvanic isolator, noise filter etc) is cumbersome at installation and risky as the operation environment vulnerabilities are not constant and typically not known in advance. Customer feedback has also shown that our filters are valued because they eliminate production stops due to false alarms/faults and homing resets caused by noise/glitches in the encoder circuits. Within-spec production (no rejects) is also ensured as correct position and workpiece dimensions are properly maintained.

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3. What operation/filtering modes do the Terminator and Mini lines offer?

There are five available modes of operation, all individually enabled via DIP switch settings:

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4. What is resolution quadrupling or 4x decoding?

The two encoder position signals (usually A and B) are identical in form but shifted 90 degrees apart in quadrature. This allows further decoding within each pulsing period into four logic states thus quadrupling the available resolution. (See also this paper).

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5. Can I use the filter with non-incremental encoders or other non-quadrature signal sources?

Yes, by disabling the Recovered modes. Typical cases are the three-phase encoder format used by servo drives to detect motor rotor position and general Clock/Direction signal pair sources.

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6. How can I check that the encoder signals are processed correctly by the filter?

By observing the three LEDs indicating the state of each filter output.  Also, checking for proper encoder operation is described here.

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7. How can I check that the receiving controller processes the filter outputs correctly?

By using the filter test facility. After making sure that no hazardous/damaging movement can result (for example, by disconnecting/disabling the motor) enable the filter test pattern generation. The controller position can then be read via any suitable means (from a connected terminal etc). Testing at different frequencies checks the linearity and bandwidth of the controller.  Finally, by using the filter reversing facility, the counting direction should also change.

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8. When was your encoder technology first employed?

Our filter technology was first employed in a flying saw application in 1995 (and has been constantly improving since then).

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9. Which motion control applications need this technology most?

Applications which see immediate improvement are:

In all cases the positioning system suffers either total position/speed loss (typically by noise in the index signal or power supply) or accumulating position drift (by mechanical vibration and common/differential noise in the lines). Another often overseen source of trouble is the motor rotor position (3phase) encoder feeding the servo drive. Our filters handle all these problems effectively. (See also this paper).

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10. What hardware subsystems/features do the Terminator and Mini lines have?

These are:

Packing all this hardware together is one of the reasons the filters are excellent value-for-money (the other reason being operational effectiveness).

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11. Is the filter's operation truly transparent?

Absolutely. The filter requires no initialization, resetting or configuration procedure and its operation is 100% transparent to the driven motion controller. As it is also powered by its own supply, it is self-sufficient in power and does not require/drain any externally sourced power. Furthermore, by powering the encoder it also relieves the controller power supply from this burden.

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12. How can I drive single-ended 5VDC/TTL inputs from the filter's EIA(RS)422 differential outputs?

By using the output signals without their complements and the output reference connections. Note however that cable length must be kept to a minimum as its capacitance limits signal bandwidth.

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13. How can I use the x4 clock/direction outputs to drive a quadrature type input stage?

As the quadrature format was originally intended, one of the signals is used to signal a step movement while the other is sampled for direction. In this case the quadrature format is essentially a clock/direction one. If however the receiving end performs quadrature decoding itself, the clock/direction pair cannot be used. (In most modern equipment the input stage format and its parameters can be programmatically set-up, so this may not be a problem).

To determine which receiver input is which (clock or direction), the test pattern facility can be used to drive the two A and B inputs first as clk-to-A/dir-to-B and then, if this does not work, as clk-to-B/dir-to-A. (Also see this FAQ).

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14. How can I check that the encoder works correctly?

By using the worn/faulty encoder detection facility.  With the filter set in any of the Recovered modes, the red "RCR" or "FLT" status LED indicates the presence of an out-of-sequence signal condition, typically caused by a damaged encoder, faulty encoder output/wiring or heavy common mode interference.  These conditions can be tested as follows.  When the LED lights-up at the same encoder angular positions and regardless of speed, then most propably the encoder disks are worn.  When the LED lights-up constantly with the encoder moving, then the encoder outputs/wiring will typically be at fault or shorted.  When the LED lights-up with the encoder standing still or randomly when moving, the filter is successfully recovering from noise and no action needs to be taken.

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15. How can I interface the universal 5 V filter inputs to 8-30 V output encoders?

By using small blocking diodes in the signal path from the encoder to the filter. The diodes effectively allow current to only flow from filter input to the encoder output when this is low. When the encoder output is high, the diodes allow the filter input to be biased by the internal pull-ups and not be affected by the higher encoder output voltage. This works with both NPN and Push-Pull encoder outputs but not with PNP types. The connection details are fully described in the filter manual and the encoder can readily be powered by the filter without any problem.

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16. Why use a filter with different input and output types?

To use as an interface between the two types. A typical case is when a differential type encoder is used in long cable runs and the PLC or drive input card processing the encoder signals is a single-ended type. In this way encoder signal bandwidth is preserved and the PLC/drive input is protected against latch-up or complete destruction from voltage spikes induced in the long cable lines (also see next FAQ).

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17. How does input stage saturation, latch-up or failure arise and how do the Terminator and Mini filters prevent it in encoder applications?

Input stage saturation, latch-up and complete failure happen when the input signal goes outside the voltage range which the input electronics can normally handle. Saturation typically occurs when the signal gets clamped by the internal power rails and extra time is required to recover input stage linearity and bandwidth. Latch-up happens when the input stage integrated circuit internal parasitic thyristor structures (all ICs have them) get triggered and in effect short the input signal to one of the power rails for as long as current can flow (usually until power is removed). If the overvoltage is outside the input electronics absolute ratings or the signal current is not sufficiently limited, the input stage will suffer catastrophic failure. Modern industrial equipment normally have sufficient protection against typical overvoltages, noise spikes and signal shorts, however when long cable runs are involved this standard protection is not enough for reliable operation in the industrial environment.

The Terminator and Mini filters address this problem effectively as they isolate, filter and individually power the encoder side and so do not allow any overvoltage spikes, noise and ground loop currents to reach the controller input stage. They are particularly effective when interfacing to typical low-cost PLC/drive single-ended inputs. (Also see this FAQ).

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18. How do I determine the filter's maximum quadrature input frequency for my encoder application?

By calculating the maximum application speed and then allowing for mechanical vibration and noise.

Given the maximum application speed V in m/min (say 60 m/min), the encoder ppr P (say 1000 ppr) and the length covered by one encoder revolution L (say 0.5 m) calculate the frequency as:

Maximum frequency = (V/60)*P/L (giving 2 kHz with the above figures)

Note that V is divided by 60 to convert to m/sec and that when the application speed is given in rpm (revs per minute), L is taken as the application revs per encoder revolution. In practice the maximum operation frequency can be ten times as much as the calculated one if mechanical vibration is present. Theoretically, the highest frequency requirement happens when two successive direction reversals happen at the encoder output circuit bandwidth.

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19. Can I use your encoder filters to process resolver noise?

Yes, our filters can be used to reject noise and dither appearing at the resolver/digital converter (R/D) output.

Typically R/D noise has two components: one caused by the conversion process and one due to mechanical vibration. Depending on its frequency, conversion noise is band-rejected or processed by the filter. Mechanical vibration effects are handled as with encoder signals.

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Administrative FAQ


1. How can I buy samples for immediate delivery?

Online here or by contacting us with your special instructions. We make every effort to have sampling quantities ex-stock for immediate worldwide shipment to you by courier within 2-3 business days.

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2. Can I buy ex-works (I have my own courier/agent)?

Yes, by contacting us with your requirements and instructions.

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3. Is there a minimum order quantity?

No, but note that shipping/handling charges become proportionally higher with smaller orders.  (You are encouraged to place small orders online and save all shipping costs).

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4. I would like to promote/market/distribute this technology in my area. What do I do?

Contact us!

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