Encoders Frequently Asked Questions
Use "Ctrl-F" to search for specific words in this FAQ.
Question:
What is the inside thread pitch of the TRD-N/NH Encoder mounting holes?
Answer
The mounting holes are
3mm diameter with .5mm thread pitch
the holes are 10mm deep
FAQ ID: 487
Question:
Do the hollow shaft encoders have the "Thru" hole or "Blind" hole?
Answer
They have the Blind hole.
FAQ ID: 619
Question:
What is the basic definition of an encoder?
Answer
An encoder comes in two architectures. The first architecture is linear (which ADC does not currently sell.) The second architecture is rotary. Both types sense mechanical motion and translates the information (velocity, position, acceleration) into useful electrical data.
FAQ ID: 819
Question:
What is the difference between an absolute and an incremental encoder?
Answer
There are a few subtle differences between absolute and incremental rotary encoders.
- Incremental encoders have output signals that repeat over the full range of motion. It is important to understand that each mechanical position is not uniquely defined. When the incremental encoder is turned on, the position of an incremental encoder is not known since the output signals are not unique to any singular position.
Absolute encoders have a unique value (voltage, binary count, etc) for each mechanical position. When an absolute encoder is turned on, the position of an absolute encoder is known (this function resembles a resolver, although the principles of operation have no similarity.)
The similarities of both absolute and incremental encoders are form factor and the issues of count and directional information. They can be obtained from both absolute and incremental encoders equally.
FAQ ID: 820
Question:
What is a channel?
Answer
A channel is an electrical output signal from an encoder. Typical incremental encoders have either two or three channels. An example would be: A, A not, B, B not, and Z, Z not (also referred to I or I not.).
FAQ ID: 821
Question:
What is quadrature and 4X (4 times) quadrature encoding?
Answer
Quadrature is a description of the 90 degrees out of phase between channel A and B.
The rising edge to rising edge (referred as the Cycle) on channel A or B indicates that one set of bars or slits (on the internal encoder disk) have passed by the optical sensor. The quadrature state of channels A and B create four unique logic states. These four unique logic states are decoded to determine distance traveled and rotation direction.
4x counting usually refers to a counter which may be configured to recognize each quadrature state as a separate count. So with this in mind 250 ppr encoder would yield 1000 individual states or edges. A 250 ppr encoder will have 250 ppr for channel A and 250 ppr for channel B.
PPR, or pulses per revolution, is another term for "line count". A line on an encoder is the physical slit on the encoder's disc that allows an optical sensor to trigger from low to high.
FAQ ID: 822
Question:
What is the Index pulse (strobe, Z, and I.)?
Answer
It is the absolute reference added to an incremental encoder. It is also known as home position. It signifies a full rotation of the encoder disk
FAQ ID: 823
Question:
How can I reduce the effect of noise when using encoders?
Answer
There are several ways to improve noise immunity. Be careful to separate motor and all power wires away from encoder wires. Always separate the channels from each other. All encoder wire should be shielded and carefully terminated. The pigtail that connects to the control unit using the encoder should be as short as possible. The leads will act as antennas for any stray RF in the vicinity. The addition of other noise suppression devices may be required in high noise environments.
FAQ ID: 824
Question:
What are "Push Pull" and "Totem Pole" outputs? Why don't they have a differential output?
Answer
Looking at the A and A not channel, the optical sensor internal to the encoder is comparing the two. If A's light amount is greater than A not, then A is high. When A is less than A not, then A is low. The same reasoning defines channel B. This process is called "Push Pull."
A "Totem Pole" output is the same as a "Push Pull" output. The big difference is the ability of the "Totem Pole" to handle sinking or sourcing less current than the "Push Pull." It is confusing because the other factor is the amount of voltage usually used to define the difference between the two. "Totem Pole" usually uses 5vdc, where as the "Push Pull" follows the input voltage. Our encoders have a range of 5-30vdc, so you will see the output referred to as both.
Our encoders that have "Totem Pole" outputs are technically categorized as open collector NPN style outputs. The only styles of differential encoder (5vdc) are our TRD - S/SHxxxx-VD models.
FAQ ID: 825
Question:
Do I need to shut down my machine to change an encoder?
Answer
The best method is to power down the unit. If the supply voltage is accidentally shorted or grounded, it will damage the encoder.
FAQ ID: 826
Question:
Q: What equipment do I need to troubleshoot an encoder?
Answer
A: An oscilloscope or specially designed encoder tester. A basic multimeter will do for basic diagnostics such as power supply and low speed pulse outputs. Any advanced pulse detection and diagnostics needs to be performed by a trained technician and an oscilloscope.
FAQ ID: 827
Question:
Can you repair an encoder?
Answer
Yes, but we do not repair them. The issue is the cost of repair. A majority of the time, the repair costs more than the replacement.
FAQ ID: 828
Question:
What is gray code?
Answer
Gray code is a form of binary. The difference is how it is incremented to the next number. Only one bit position can increment at a time.
Gray code: 0, 1, 3, 2, 6, and 7
Binary: 0, 1, 2, 3, 4, and 5
We carry 5 bit /32 resolution thru 11 bit /2048.
See also Application Note AN-SEN-003: Mechanism of Absolute Rotary Encoders
FAQ ID: 829
Question:
What are Excess Gray Codes?
Answer
See this page for an explanation and table of Excess Gray Codes:
http://support.automationdirect.com/notes/encoder_graycode.html
FAQ ID: 1587