Redundancy Groups [Image: redundancyGroup.png]

A redundancy group represents a collection of items which are redundant to one

another to provide a greater group reliability in the context of a system. The standby

redundancy group consists of items arranged vertically, with a fraction indicating

which items are hot/functioning (numerator) out of the total number of redundant items

in the group. All items in a standby redundancy group have a .

[Image: standbyredundancy.png]

Items are classified as either "hot" or "cold" standby. In hot

standby, items is active and ready to immediately take on the extra loads required

should another item fail. A part that is in hot standby accumulates "life"

i.e. wear and tear during its operational period. Items in a standby redundancy group

are classified as "cold" standby. A part in cold standby is not operational

until it is required to assume the load/role of another failed item. An item that is in

cold standby accumulates no life until it is activated.

Expressing cold redundancy mathematically for the Exponential Distribution type:

[Image: redundancyexpeq.png]

Where n is the total number of items in a group, k is the number of

working items in a reliability group that must be functioning for the group to

function, λ is the exponential failure rate, t is the duration of

operation and i is the item counter.

Expressing cold redundancy mathematically for the Weibull Distribution type:

[Image: redundancyweibeq.png]

Where β is the Weibull slope and η is the characteristic life

of the item.

The number of redundant items that need to fail in order for the entire group to

fail is defined as "K out of N" failures, where n is the

number of failed items and m is the total number of redundant items. The failure

rate/reliability of the group will be based on the likelihood of operating with

n failed items simultaneously.

To create a Standby Redundancy Group:

1. Right-click an the item in the Project explorer or System Model
2. Select 'RBD Model' Note: The RBD editor will show all items under the currently

selected item.

3. In the RBD editor, select items (hold SHIFT and left-click) to include in the Standby Redundancy group
4. Right-clicking the RBD diagram and selecting "Group → Standby Redundancy Group" from the right-click menu Note: An alternative method is to select the redundancy icon

[Image: redundancyGroup.png]

from the icon menu to

create the standby redundancy group.

5. Verify that all selected items have been included in the standby redundancy group

[Image: createredundancy.gif]

Toggling Functioning Items

To define the number of functioning items in standby redundancy group:

1. Open the RBD editor for an item containing a standby redundancy group
2. Select the group and view the Properties viewer
3. In the General tab select the toggle to increase or decrease number of functioning items (The number of failed group elements required for group failure)
4. Review the change in reliability for the standby redundancy group or the RBD analysis
5. Save changes