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Encoder Basics

Posted: Mon Mar 15, 2010 2:56 pm
by admin
Encoders Basics

1. Encoder Type:
Centroid MPU11 based CNC hardware (Oak, Allin1DC, Acorn) requires quadrature, differential encoders which operate on 5VDC. This is the most common type of encoder. Encoders labeled "TTL type" (non differential) are unsuitable, and fortunately are quite rare.

2. Encoder Signals:
a) The following signals must be present and wired: A, /A, B, /B, Z, /Z, +5VDC and ground.
Note: The Z channel is sometimes labeled as I, C or "marker". The "/" symbol may also be
expressed as "-", "NOT" or "!" or a line over the letter, it means the signal is the complement
(opposite) of the channel specified.

b) Signal levels:
The "low" signal level must be less than 0.5 VDC and the "high" signal level must be at least 3.5 VDC.

3. Encoder Resolution:
Typical Machine tool applications (milling machines, lathes and routers) require at least 1000 line (4000 counts per rev) encoders, We recommend and sell 2000 line (8000 counts per rev) encoders. To achieve reasonable accuracy and smooth motion, the encoder/motor/ballscrew configuration must achieve a minimum resolution of 20,000 encoder counts per inch of travel (787 counts/mm). A typical knee mill which uses a 5tpi (turns per inch) ballscrew and has the motors belted at a 1:1 ratio, a 1000 line encoder just meets the minimum counts per inch at 20,000 for smooth motion, this will work however a 2000 line encoder (8000 counts per rev) would be a better choice. Older 250 and 500 line encoders will not work to satisfaction.

some examples

5 turns per inch ballscrew belted at 2:1 with the servo motor = 10 turns of the servo motor per inch of axis travel

10 turns per inch x 4000 counts per rev (1000 line) = 40,000 counts per inch

10 turns per inch x 8000 counts per rev (2000 line) = 80,000 counts per inch.

5 turns per inch ballscrew belted at 1:1 with the servo motor = 5 turns of the servo motor per inch of axis travel

5 turns per inch x 8000 counts per rev = 40,000 counts per inch of axis travel.

4. Encoder wiring MUST be shielded, twisted pair cabling.

Encoder wiring at MPU11:
DB9 Body = Cable Shield

Pin Function
1 No Connection
3 Z\
4 A\
5 B\
6 Z
7 A
8 B
9 +5 VDC
db9m-solder side.gif
db9m-solder side.gif (1.3 KiB) Viewed 21388 times
db9m-pin side.gif
db9m-pin side.gif (1.16 KiB) Viewed 21388 times

Re: Encoder Basics

Posted: Tue Mar 23, 2010 9:58 pm
by cnckeith
We sell 2000 line (8000 counts per revs) encoders that accept common sized motor encoder shafts on our website. In stock ready to ship for only $175 each.
with connectors.

2000 Line Encoder (8000ppr)
This differential encoder not only suppresses noise in the system that can be harmful to encoder signals, but also outputs a quadrature signal giving 8000 counts per revolution of the motor. This is ideal for machines already equipped with DC brush servos to enhance the speed and precision of the machine. Available in 6 mm, 1/4", 3/8", and 1/2" hollow shaft sizes
comp_encoder_large.jpg (44.95 KiB) Viewed 21317 times

Re: Encoder Basics

Posted: Sun Mar 28, 2010 11:13 am
by Metalstech
I've got a bit of a discrepancy with the MPU11CBL.S01 file, encoder pin-out labeling and your labeling of the encoder in the basic encoder post.
According to the post, pin 4= A/ and pin 5= B/.
The drawing I mentioned shows pin 4= B/ and pin 5 =A/.
What is the correct labeling?
Thanks, Metalstech

Re: Encoder Basics

Posted: Mon Mar 29, 2010 9:30 am
by diycncscott
Hi Metalstech,

The pinout in the drawing above is correct. You apparently have an obsolete version of the MPU11Cable document.

Current document

I have attached the current version of the document in pdf format in the link below:
(75.5 KiB) Downloaded 1565 times

Re: Encoder Basics

Posted: Thu Apr 01, 2010 7:55 pm
by Metalstech
Fantastic job on keeping up with the Q and A! Thank you all of you guys at AJAX and those out there pitching in with the help.
Thank you,

Re: Encoder Basics

Posted: Fri Apr 02, 2010 6:39 am
by diycncscott
Hi guys,
Where page space and time permits, please post content rather than a link to a document or page outside of the AjaxCNC Support Forum. Content is easier to follow, it's searchable and provides immediate assistance to the user. Most importantly, content won't break. Links outside of the AjaxCNC Support Forum -even AjaxCNC links- will break if the document is moved or renamed. Links (with a short explanation) to other posts within the AjaxCNC Support Forum are acceptable.

FWIW We will begin posting all documents in pdf and Open Office formats. Open Office is a free office suite with the capability of opening, editing and saving in Word, Excel, Publisher, PDF, Powerpoint etc... I'll be adding post with more complete information shortly but, in the meantime, check it out at I highly recommend it.

What are the wire colors of the encoder pigtail?

Posted: Mon Apr 05, 2010 3:21 pm
by Centroid_Tech
Question: Somehow the encoder pigtail was damaged. What are the wire colors of the encoder pigtail?

Pin Signal Color
1 A Blue
2 A/ Blue/Black stripes
3 B Green
4 B/ Green/Black Stripes
5 Z Violet
6 Z/ Violet/Black Stripes
7 Vcc Red
8 GND Black
9 Shield Heavier Black wire

Re: Encoder Basics

Posted: Mon Aug 20, 2012 1:29 pm
by naxus
this card accept encoder HEIDENHAIN "ROD420" (TTL 1250 IMP.)???

Re: Encoder Basics

Posted: Mon Aug 20, 2012 4:08 pm
by Centroid_Liviu
Encoders labeled "TTL type" (non differential) will not work with our control. We have 2000 line (8000ppr) encoders in 6 mm, 1/4?, 3/8?, and 1/2? hollow shaft sizes available if you need to swap yours out.

Re: Encoder Basics

Posted: Wed Sep 05, 2012 9:01 am
by Mountainman
Anybody have clear written instructions on installing encoder to SEM servo motor. Any warning out there on what I should not do or be careful of ? I have a 1991 Bridgeport V2XT. I've seen the tutorial, but I am sure a pic means one thing to one person and something else to another.