Encoder Considerations; Supported Encoders; Encoder Diagnostics; General Encoder Diagnostics - Allen-Bradley PowerFlex 755 User Manual

Encoder Considerations

Table 8 - Supported Feedback Cards and Encoder Types
Primary Channel
Feedback Option
Encoder Type
20-750-UFB-1 Sine/Cosine
20-750-DENC-1 Digital AqB
This section describes factors to consider when using an encoder with the
Integrated Safety Functions option module.

Supported Encoders

Table 8 describes the supported encoder types based on the feedback card that
is used and the physical terminal it is connected to. You must determine the
safety capability of a system based on the supported encoder types and the
encoder diagnostics that are described in this chapter.
Secondary Channel
Encoder Motion Axis Encoder Type
Not Used
Digital AqB
Motor Feedback
Not Used
Digital AqB

Encoder Diagnostics

Depending on the encoder type, the module performs several diagnostic tests
on encoder signals to detect faults in the encoder. You must determine if the
combination of the selected encoder device type and the diagnostics that are
described in this chapter will satisfy the required safety function rating. The
use of non-safety, standard encoders my require further analysis and assessment
activies.

General Encoder Diagnostics

The following encoder diagnostics are available for all supported encoder
types:
• Encoder Voltage Monitoring (Configurable)
• Maximum Speed Limit (Configurable)
• Maximum Acceleration (Configurable)
• Maximum Encoder Input Frequency
• Dual Encoder Velocity and/or Position Discrepancy (Configurable)
Encoder Voltage Monitoring
The voltage monitoring diagnostic samples the voltage being supplied to the
encoder to help ensure that its level is within its configured range. If the voltage
monitoring diagnostic detects a voltage that is out of the configured range, the
safety feedback instance reports a voltage monitoring fault and causes the
module to enter the safe state.
Rockwell Automation Publication 750-UM005A-EN-P - October 2018
About Safe Stop and Safe Monitor Functions
Achievable System Safety Rating
Encoder Motion Axis
Not Used SIL 2/PL d with safety rated encoder
Load Feedback SIL 3/PL e
Not Used SIL 2/PL d with safety rated encoder
Load Feedback SIL 3/PL e
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