Allen-Bradley PowerFlex 70 Reference Manual

2-126 Overspeed Limit
Overspeed Limit The Overspeed Limit is a user programmable value that allows operation at
maximum speed but also provides an “overspeed band” that will allow a
speed regulator such as encoder feedback or slip compensation to increase
the output frequency above maximum Speed in order to maintain maximum
Motor Speed.
Figure 2.27
illustrates a typical Custom V/Hz profile. Minimum Speed
determines the lower speed reference limit during normal operation.
Maximum Speed determines the upper speed reference limit. The two
“Speed” parameters only limit the speed reference and not the output
frequency.
The actual output at maximum speed reference is the sum of the speed
reference plus “speed adder” components from functions such as slip
compensation, encoder feedback or process trim.
The Overspeed Limit is added to Maximum Speed and the sum of the two
(Speed Limit) limits is output. This sum (Speed Limit) is compared to
Maximum Frequency and an alarm is initiated which prevents operation if
the Speed Limit exceeds Maximum Frequency.
Figure 2.27 Typical V/Hz Curve for Full Custom (with Speed/Frequency Limits
Frequency
Output Voltage
Note 1: The lower limit on this range can be 0 depending on the value of Speed Adder
Overspeed
Limit
Frequency Trim
due to Speed
Control Mode
Maximum
Voltage
Motor NP
Voltage
Run
Boost
Break
Voltage
Start
Boost
Allowable Output Frequency Range - Normal Operation
1
Allowable Speed Reference Range
Allowable Output Frequency Range -
Bus Regulation or Current Limit
Maximum
Frequency
Motor NP Hz0 Break
Frequency
Maximum
Speed
Minimum
Speed
Output
Frequency
Limit

Allen-Bradley PowerFlex 70 Specifications

General

Brand	Allen-Bradley
Model	PowerFlex 70
Category	Controller
Language	English