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1. What is an encoder?
2. What is the difference between Differential and Single Ended outputs?
3. Can I use a Quadrature Output signal to detect change in direction?
4. What is the difference between an incremental encoder and an absolute encoder?
5. What is Push-Pull output?
6. What is an Open Collector Output?
7. Why use open collector?
8. What is Gray Code?
9. Can Gray Code be converted to Binary?
10. How do I calculate output Frequency of an Incremental Encoder?
1. What is an encoder?
A. A rotary encoder, also known as a shaft encoder, is an electro-mechanical device used to
convert angular position of a shaft to a digital or analogue signal.
2. What is the difference between Differential and Single Ended outputs?
A. An encoder with single ended output has one set of signals A channel, B channel and
One Marker Pulse. This method is more susceptible to electrical noise. A differential
encoder has the same signal set as a single ended encoder with and additional set of
Complimentary or “mirror image” signals. The complimentary signal is the exact inverse
of its main signal. For example: if 'A' channel is in the High state, A complimentary
will be in a low state. This feature is extremely important to increase noise immunity.
3. Can I use a Quadrature Output signal to detect change in direction?
A. Yes. The term Quadrature is when there is two output signals 90 electrical degrees out of phase from
each other. The signals can be configured with A channel leading B channel in the Clockwise Direction or
B channel leading A channel in the clockwise direction. Since the signals are offset by 90 electrical
degrees this allows the controller to monitor and determine the direction the encoder shaft is rotating.
4. What is the difference between an incremental encoder and an absolute encoder?
A. With an incremental encoder relative position can be measured by counting the number of pulses
produced. Alternatively by measuring the frequency of these pulses relative speed can be determined. An absolute
encoders measures absolute position, and has the ability to maintain position information even in the event of a
power loss condition.
5. What is Push-Pull output?
A. Push-Pull also known as Totem Pole is a line driver that will sink or source current depending on the load
applied. It has the advantage of being universal in NPN or PNP interfacing, with the added benefit of higher
frequency capability. (300KHz) In general Push-Pull will directly replace NPN or PNP circuits as long as
they are not of the Open Collector type.
6. What is an Open Collector Output?
A. An Open Collector output comes in two forms. It can be a NPN transistor or a PNP transistor.
A NPN transistor will pass vthe current through its emitter to ground. Known as “Current sinking” A PNP
transistor does the same as except it passes current through its collector to ground. Known as ‘Current
Sourcing” NPN transistors consist of a layer of P-doped semiconductor (the "base") between two N-doped
layers. A small current entering the base in common-emitter mode is amplified in the collector output. In
other terms, an NPN transistor is "on" when its base is pulled high relative to the emitter. PNP transistors
consist of a layer of N-doped semiconductor between two layers of P-doped material. A small current leaving
the base in common-emitter mode is amplified in the collector output. In other terms, a PNP transistor is "on"
when its base is pulled low relative to the emitter. Although both are available, NPN is far more widely used than PNP.
7. Why use open collector?
A. The only reason that you would use an NPN Open Collector output is when the Supply Voltage is different
that the signal logic level required. The open collector format allows the collector of the transistor
to be connected to a power source that is different from the main power supply. For example: Power Supply
is 5 Volts and the output signal needs to be 24 Volts.
8. What is Gray Code?
A. Gray code is similar to Binary code, however unlike Binary Code; Gray Code has the property
that only one bit changes in moving from one state to the next. There are many benefits of using
Gray Code over Binary Code, one of which is the ability to reduce errors in some systems.
For
example: If binary were used, there would be no way to ensure that all bits will change
simultaneously at the boundary between encoder positions.
9. Can Gray Code be converted to Binary?
A. Yes. Gray code is an Exclusive Or Logical Function of Binary.
10. How do I calculate output Frequency of an Incremental Encoder?
A. You must know at least two of the parameters.
Frequency = (PPR X RPM) / 60
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