The flow-down described in this chapter can be applied to a variety of parameters, including mechanical, electrical, and software parameters. In Figures 10.14, 10.15, and 10.16, qualitative flow-down will be applied to three critical parameters for a set of communication devices for secret agents; the device is code-named "Simon." These critical parameters are water resistance, secure communication, and programming time for multiple units. By sheer coincidence, the first critical parameter is primarily a mechanical engineering example, the second is a combined software and electrical engineering example, and the third is primarily a software example.
Figure 10.14 Critical parameter flow-down of water resistance for "Simon" communication device
Figure 10.15 Critical parameter flow-down of secure communication for "Simon" communication device
Figure 10.16 Critical parameter flow-down of programming time for multiple units
Water resistance is largely dependent on the materials used in the housing (outer shell) of the communication device and the effectiveness of the seals involved in the opening in the housing to accommodate a microphone. The mechanical engineering design team is confident that the housing itself is impervious to water intrusion, and the primary risk is seal for the microphone. The team has identified the x's as the housing opening diameter, the microphone outer diameter, and the outer diameter of an O-ring that must not exhibit excessive compression. The design team is also concerned with vibration as a noise. The ultimate customers (spies, secret agents, and informers) are prone to considerable vibration in the usage environment, as the team ascertained through exhaustive research (watching James Bond movies; popcorn optional). This example is similar to an actual DFSS project, which is shared as an example for optimization and flow-up in Chapter 14.
The design team flowed-down secure communication (measured by a secure communication effectiveness metric) to a software parameter (cipher code effectiveness) and several subordinate y's, including the center frequency of the voltage-controlled oscillator (VCO). This subordinate y was flowed down to parameters associated with the two capacitors, an inductor, a varactor, and the voltage applied to the varactor, as shown in Figure 10.15.
The team also flowed down the requirement for the time required to program a set of communication devices, as shown in Figure 10.16.