Читать книгу System Reliability Theory - Marvin Rausand - Страница 134

Consider a sink faucet used in a bathroom. The main functions of the faucet are to open/close the water supply, to contain the water, and to regulate the water temperature and flow. We consider only the faucet (the item) and assume that cold and hot water are available.

The faucet may have a number of failure modes. Among these are:

1 Fail to open (on demand) and supply water

2 Fail to close (on demand) and stop the flow of water

3 Leakage through the faucet (i.e. dripping)

4 Leakage out (from faucet seals)

5 Fail to regulate water flow

6 Fail to regulate temperature

The faucet has two main states, closed and open. The first two failures (1 and 2) occur during intended transitions between these states. The next two failure modes (3 and 4) occur in a state. For these failure modes, the faucet is in a state where it is leaking and not able to perform as required. The two last failure modes (5 and 6) may be interpreted to be somewhere between the two other types.

Example 3.9 shows that a failure mode sometimes describes the “manner by which a failure occurs” and sometimes the “manner by which a fault is present.”