PowerFlex 755T Emergency Override Function

Question

On a PowerFlex 755T, what is emergency over-ride and how does it work?

Answer

The purpose of the function is to allow the drive or bus supply to override its internal protections (faults) in emergency situations. This function is important for applications where customers would trade product longevity for continued running during an emergency situation.

Setting the Mode

There are two modes for the function: Only Override and Purge Frequency.

Go to the Overrides group in the Protection file on port 0.

Go to parameter 0:454 [Emerg OVRD Mode] and select the desired mode.

Only Override

In Only Override mode, the product overrides faults to continue running. It uses its normal methods for starting and stopping. It follows its regular position/velocity/torque mode.

Purge Frequency

In the Purge Frequency mode, the product overrides faults to continue running. It switches to velocity mode and uses the Purge Frequency as its velocity reference. The function treats the Emergency Override command like a Run command. It runs at the Purge Frequency when the command is set, and stops when the command is cleared.

To set the Purge Frequency, go to parameter 0:457 [Purge Frequency] and enter the speed value.

Deciding How to Activate the Feature

You can activate the feature via a bit in the controller to product logic command word, or by discrete-wired digital input.

Logic Command

Program the Logix project to set bit 15 ‘Emerg OVRD’ to create an Emergency Override command.

Discrete-Wired Digital Input

Use parameter 0:134 [DI EmergencyOVRD] to select a digital input on an I/O option card in one of the option slots. Wire the input to circuitry that closes or energizes to create an Emergency Override command, and opens or de-energizes to remove the Emergency Override command.

Go to the Command group in the Feedback and I/O file on port 0.

Program it to clear the bit to remove the Emergency Override command.

Go to parameter 0:134 [DI EmergencyOVRD] and map the function to the input on the option card you have wired to the circuit.

Interaction between Logic Command and Digital Input

You cannot use both methods in the same configuration. The digital input takes priority over the logic command. If you choose to configure the digital input function, by selecting a nonzero value in parameter 0:134 [DI EmergencyOVRD], bit 15 ‘Emerg OVRD’ in the Logic Command is disabled.

Deciding Which Protections to Override

The person or company that designs the drive or bus supply configuration is responsible for deciding which protections the function can override. That person or company takes responsibility for the damage to the product from the conditions that would otherwise trigger the protections.

Go to the Overrides group in the Protection file on port 0.

Go to parameter 0:455 [Emerg Prot OVRD].

Set bits in parameter 0:455 [Emerg Prot OVRD] to configure the product to override classes of protection. Each bit represents a class of protections or faults. Set a bit to override that class of faults. Clear a bit to allow the class of faults to stop the drive or bus supply.

Here are two examples.

  • Bit 0 ‘LS Ctrl Flts’ represents the faults from line side control (port 13). If the engineer sets this bit, these events do not stop the product (drive or bus supply). If the engineer leaves it cleared, these events stop the product.
  • Bit 1 ‘LS Pwr Flts’ represents the faults from the line side power (port 14) that can be overridden.

The programming manual describes which faults are covered by each bit. See the description for parameter 0:455 [Emerg Prot OVRD]. Also, see the fault and alarm tables in the troubleshooting chapter.