Reliability HotWire

Reliability HotWire

Issue 123, May 2011

Tool Tips

*How can I install ReliaSoft software without having to provide user input during installation?

Standard software installations usually require that the user interact with the computer during the installation process. For example, the user may need to click Next > at certain stages of the installation, select I Accept when presented with a license agreement or click Finish towards the end of the installation process.

However, as of February 2011, the installation programs for many of ReliaSoft’s products (including Weibull++, ALTA, DOE++ and BlockSim) will accept command-line options for performing unattended installations—i.e., installations that do not require routine user inputs such as those mentioned above. Unattended installations are especially useful when, for example, multiple applications need to be installed onto multiple machines. In situations like these, one can save time by running custom installation scripts that perform a series of unattended installations.

For a full listing of the affected ReliaSoft products and information on performing unattended installations of these products, see Technical Support document # RS40013.

*How can I use the Duty Cycle property in BlockSim?

In BlockSim the duty cycle property allows you to model situations where the actual usage during the operation of a component, subsystem or system is not identical to the usage for which you have data, either from testing or from the field. This can include situations where the item:

  • Does not operate continuously (e.g., a DVD drive that was tested in continuous operation, but in actual use within a computer accumulates only 18 minutes of usage for every hour the computer operates).

  • Is subjected to loads that are greater than or less than the rated loads (e.g., a motor that is rated to operate at 1000 rpm but is being used at 800 rpm).

  • Is affected by changes in environmental stress (e.g., a laptop computer that is typically used indoors at room temperature, but is being used outdoors in tropical conditions).

In these cases, continuous operation at the rated load is considered to be a duty cycle of 1. Any other level of usage is expressed as a percentage of the rated load value or operating time. Thus, for the examples given above:

  • The duty cycle for the DVD drive is 18 min / 60 min = 0.3.

  • The duty cycle for the motor is 800 rpm / 1000 rpm = 0.8.

  • For the laptop, the duty cycle is determined based on the intended operating conditions and on engineering knowledge about how increased temperature and humidity affect the system. In this case, suppose that testing has shown that the tropical conditions increase the stress on the components of the laptop by a factor of 1.5. Thus, the duty cycle is 1.5.

In BlockSim 7, the duty cycle property can be applied to blocks in RBDs and to operational phases in phase diagrams.

Duty Cycles

In RBDs, you can assign various duty cycles to individual components in a diagram. Alternatively, you can assign the same duty cycle to all components in a diagram, thereby applying that duty cycle to the entire assembly or system represented by the diagram. In phase diagrams, you can assign various duty cycles to individual operational phases to represent varying use levels during the system mission (e.g., the varying stress on an aircraft engine during taxi, take-off, cruising and landing). You can also use a phase diagram as a quick way to apply a duty cycle to an entire RBD by creating a phase diagram that contains a single operational phase and assigning a duty cycle to the phase.

In cases where multiple duty cycles apply, their effect is compounded. This can happen either within an RBD or where a phase duty cycle interacts with a duty cycle within the RBD. Assume, for example, that the DVD drive mentioned above is part of the laptop also mentioned above. If you were to model the tropical use conditions within an RBD, you would need to multiply the duty cycle for every component in the laptop by the laptop’s duty cycle of 1.5. For components that normally operate continuously at rated load in the laptop (i.e., components that have a duty cycle of 1), the duty cycle would be 1 x 1.5 = 1.5. The duty cycle for the DVD drive would be 0.3 x 1.5 = 0.45. If you chose, instead, to use a phase diagram to apply the laptop duty cycle, all duty cycles in the RBD would be at their original values (e.g., the DVD drive’s duty cycle would be 0.3). The multiplication of duty cycles would be automatically performed upon simulation of the phase diagram.