1. Incremental and Absolute with PowerFlex 750 series Drives
Encoders
Incremental and Absolute with PowerFlex 750 series Drives
Sam Deligio
Project Application Engineer – LV Drives
1/26/19

2. Agenda Encoder Overview Terminology Incremental Encoders
Absolute Encoders
Common Problems

3. What is an Encoder?
An Encoder is a device that converts mechanical motion into electrical signals to determine machine position and/or velocity
Encoders are categorized as Incremental or Absolute
Motion
applied
to shaft

4. What is an Encoder? Commonly mounted on motor
Encoder installation
Commonly mounted on motor
Can be used on machine/load
Shafted/Hollow Shaft/Laser/Magnetic
Position/Velocity can be sent to a VFD or device for control
1 drive/1 encoder (common)
1 drive/many encoders (motor/load)
Many drives/1 encoder (master encoder)
Motor
Adapter
Encoder

5. Agenda Encoder Overview Terminology Incremental Encoders
Absolute Encoders
Common Problems

6. Feedback Device Terminology
Quadrature
Does not mean 4 signals
Uses two square wave signals (A/B) 90 degrees out of phase-used for direction (counts up/down)
Senses rising and falling edges from both channels
A-Channel Only (Non-Quadrature)
No B signal (rising edges only)
Can detect motion but not direction (counts up)

7. Feedback Device Terminology
Differential
A pair of signals that are logically opposite (A/Anot, B/Bnot, or Z/Znot)
Single-Ended (Non-Differential)
A single output that is referenced to common (A, B, or Z)

8. Feedback Device Terminology
Differential
Single Ended (Non-Differential)
Quadrature
A-Channel only (Non-Quadrature)

9. Feedback Device Terminology
Pulses Per Revolution (PPR)
Total Number of positions/pulses in one revolution
Edges Per Revolution (EPR)
Total number of edges (counts) interpreted by feedback card in one revolution (Rising or rising/falling)
Index or Marker Pulse (Z Channel)
Pulse that occurs once per encoder revolution
Used a reference point
Resolution
The measure of the smallest change of input that the encoder can detect

10. Encoder Types Incremental Simple (Low cost)
Position NOT retained after power loss (0 on power up)
Homing needed for positioning
Commonly Lower Resolution
Absolute
Complex
Position retained after power loss
Typically no Homing needed for positioning
Commonly Higher Resolution
Refer to 750-IN001 manual for encoder compatibility

11. Agenda Encoder Overview Terminology Incremental Encoders
Absolute Encoders
Common Problems

12. Optical Encoder Operation
Resolution depends on the number of slots on the code disk
Use when retention of position data is not required when power is lost
Basically counts up or up/down

13. Differential signals are used to achieve better Signal-Noise Ratio
Incremental Output
Depending if A leads B or B leads A, the a controller can detect direction and add/subtract position
When using a differential signal, noise is cancelled
Differential signals are used to achieve better Signal-Noise Ratio

14. PPR vs EPR PPR = Pulses per revolution 1024 typical
EPR = Edges per revolution
Also known as Counts/Rev
A channel only (Rising edge only)
1024 * 1 rising edge = 1024 EPR
Quadrature (Rising and Falling)
1024 *(2 rising) * (2 falling) = 4096 EPR

15. PPR vs EPR
Encoder config (PowerFlex 750 feedback card) has A Chan Only (Quadrature setting) and Single Ended (Differential setting)
Notice: EPR doesn’t change when Single Ended is on/off
Single Ended On
Single Ended off
A Chan Only On
Signals: A
PPR: 1024
EPR: 1024
Signals: A, Anot
A Chan Only Off
Signals: A, B
EPR: 4096
Signals: A, Anot, B, Bnot

16. Resolution Number of divisions per unit of motor output
Smallest distinguishable increment into which a signal or quantity can be divided
Example:
Encoder produces 1,024 pulses/rev
Motion of 1/1024th of a rev generates a pulse

17. Determining Required PPR
You want to achieve a speed accuracy of 0.1 Hz with A quad B w/ 4 pole motor
𝑆𝑝𝑒𝑒𝑑 𝑅𝑒𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝐻𝑧 = 1 𝐸𝑃𝑅 𝑥 𝑀𝑜𝑡𝑜𝑟 𝑃𝑜𝑙𝑒 𝑃𝑎𝑖𝑟𝑠 10_3 𝑠𝑒𝑐
0.1 𝐻𝑧= 1 𝐸𝑃𝑅 𝑥 2 10_3 𝑠𝑒𝑐 =20,000 𝐸𝑃𝑅
20,000 𝐸𝑃𝑅 4 (𝑄𝑢𝑎𝑑) =5,000 𝑃𝑃𝑅 𝑜𝑟 𝑏𝑒𝑡𝑡𝑒𝑟 𝑛𝑒𝑒𝑑𝑒𝑑

18. PowerFlex 750 ENC and DENC Setup
For use with incremental encoder (PF753 or PF755)
Set PPR (P2/12 for Enc0/Enc1)
Configure signals (P1/P11 for Enc0/Enc1)
Set direction to match motor
Auto set when Direction test used
Set feedback select to encoder
Ex: Port 00 P125
Safety jumper must be set on DENC if using a 750 series safety card

19. PowerFlex 755 UFB Setup
For use with incremental encoder (PF755 only)
Set Device Select (P6/36 for FB0/FB1)
Set PPR (P15/45 for FB0/FB1)
Configure signals (P16/P46 for FB0/FB1)
Set direction to match motor (P8/P38 for FB0/FB1)
Auto set when Direction test used
Set feedback select to encoder
Ex: Port 00 P125
Safety switches must be set on UFB if using a 750 series safety card

20. Agenda Encoder Overview Terminology Incremental Encoders
Absolute Encoders
Common Problems

21. Absolute Encoders Every position has a unique pattern for 1 rev
Number of bits dictate resolution
3 bit resolution = 23 bit counts = 8 counts
10 bit resolution = 210 bit counts = 1024 counts
Main Advantage: Position retained after power up
Typically no homing needed

22. Absolute Encoders Multi-Turn Absolute Single-Turn Absolute
Is used when full range of positioning in the application is not greater than one full revolution (360 degrees) of the encoder shaft
Example: Rotary table positioning
Multi-Turn Absolute
Is used when full range of positioning in the application requires multiple turns of the encoder shaft
Example: Lead and ball screw applications
Only Universal Feedback Board (UFB) supports absolute encoders

23. Absolute Encoder Types
Four main types
Hiperface – High Performance Interface
Protocol for Stegmann Devices
Uses Sine/Cosine and data channel
Can write configuration data to UFB
Available on A-B MP motors
SSI – Serial Synchronous Interface
May be full digital or digital and sine/cosine signals
Cannot write configuration data to UFB

24. Absolute Encoder Types
BiSS – Bidirectional Serial Synchronous Interface
May be full digital or digital and sine/cosine signals
Can write configuration data to UFB
EnDat – Encoder Data
Protocol for Heidenhain Devices
V2.1 supports Absolute (Similar to Hiperface Sine/Cosine)
V2.2 supports Absolute and Incremental (Full Digital)
Similar to SSI and BiSS with no Sine/Cosine

25. Absolute Resolution
High Resolution: using Sine/Cosine feedback and PowerFlex drives
12/20-12 bits for turn / 20 bits for position within a rev
Points are interpolated between counts (210 bit =1024; 10 extra bits)
1024 counts/rev * 1024 interpolated points = 1,048,576 counts/rev
2048 counts/rev * 512 interpolated points = 1,048,576 counts/rev

26. Absolute Resolution 24-bit Resolution (P8/P38 for FB0/FB1)
12/20 bit 8/24 bit
210 bit =1024; 14 extra bits 214 bit =16,384
1024 counts/rev * 16,384 interpolated points = 16,777,216 counts/rev
Turns reduces
212 bit = 4096 turns
28 bit = 256 turns

27. PowerFlex 755 Setup (Absolute)
Requires UFB-1 option module
Setup depends on encoder type
Set Device Select (P6/36 for FB0/FB1)
Set direction to match motor (P8/P38 for FB0/FB1)
Auto set when Direction test used
Hiperface, BiSS (not manual), and EnDat write to other configuration parameters
BiSS (manual) and generic Sine/Cosine set PPR (P15/45 for FB0/FB1)
Set feedback select to encoder
Ex: Port 00 P125

28. PowerFlex 755 Setup (Absolute)
SSI (Full Digital or Sine/Cosine)
Set Device Select (P6/36 for FB0/FB1)
Set direction to match motor (P8/P38 for FB0/FB1)
Auto set when Direction test used
SSI Cfg (P20/50 for FB0/FB1)
SSI Resolution (P21/51 for FB0/FB1)
SSI Turns (P22/52 for FB0/FB1)
Set to 0 if single turn

29. Agenda Encoder Overview Terminology Incremental Encoders
Absolute Encoders
Common Problems

30. Common Encoder Problems
Speed feedback doesn’t match actual feedback
PPR entered wrong into VFD
Rotate motor 10 times and monitor at feedback counts
Absolute Encoder parameters setup incorrectly
Verify wiring of encoder
Verify parameters settings from encoder datasheet
Encoder is not supported
Refer to 750-IN001 for encoder specifications
Permanent magnet motors: motor feedback device must have a resolution so that the number of pulses per revolution (PPR) is an exponent of two

31. Supported Encoders (ENC and DENC)

32. Supported Encoders (UFB)
A quad B (5v only)
PF753 does not support UFB
Absolute Encoder

33. Common Encoder Problems
Wiring issues
Direction incorrect – Change A and Anot or B and Bnot
A/B or Sine/Cosine signals swapped
Encoder shields not terminated properly
Encoder not mounted to motor tightly
Issues seen at faster speeds
Run open loop and monitor encoder feedback
Max encoder frequency exceeded
Max motor RPM w/ encoder = (max enc freq * 60)/PPR
250 kHz * 60/1024 = 14,648 RPM
Hi-Res max input frequency = kHz

34. Open Loop Test
If possible, an open loop test can point to a feedback issue
In Speed mode
Set Pri Vel Fdbk Sel to open loop
Set Aux Vel Fdbk Sel to encoder
Start the drive run to set speed
Compare Pri Vel Fdbk and Aux Vel Fdbk
If opposite, direction is backwards
If Aux Vel Fdbk = 0 or not the same
Wiring, Parameter Setup, or Mechanical Connection

35. Common Drive Faults Open Wire
Signal A,B, or Z are in the same state as their ‘Not’ signals
Phase Loss
More that 30 open wire events occurred in 8 ms
Quadloss
Of A and B signals, either one was detected twice without other one
Must happen 10 times in 10 ms

36. ENC and DENC Troubleshooting
Enc x Error Status
P6/16 for Enc0/Enc1
Enc x Status
P5/15 for Enc0/Enc1
Shows ABZ signals

37. UFB Troubleshooting Verify Feedback Identify P7/37 for FB0/FB1
FBx Status can show errors
P10/40 for FB0/FB1
FBx Inc Sts
P14/47 for FB0/FB1

38. Reference Rockwell Automation Literature Library
Manuals, certifications, installation instructions
PowerFlex 750 Installation Instructions Pub 750-IN001
PowerFlex 750 Programming Manual Pub 750-UM001
Rockwell Automation KnowledgeBase
Technotes for setup and troubleshooting

39. Questions?