Availability Factors

Availability means getting the right component when it is needed

A system is made from components that work together to perform a function. Selecting a component therefore involves more than checking that it works: the designer must also consider whether enough of it can be obtained, reliably and in time for manufacture.

Availability affects the choices a designer can make. A component that performs well but cannot be delivered when needed may hold up the assembly of the whole product. Designers need to balance the system’s technical requirements against the reliability of its supply.

Stock materials and components: designing around standard options

Stock materials are standard materials or components normally supplied off the shelf. In electronic systems, examples include resistors supplied in standard resistance values. Rather than commissioning a special component, a designer can select a suitable item from a supplier’s existing range.

Using stock items usually reduces lead time: the time between ordering and receiving an item. It can also reduce cost because the item does not need to be specially made. Readily available replacements can make later repairs easier too.

For example, if a standard $10\,\text{k}\Omega$ resistor meets a circuit’s requirements, choosing it avoids the need to order a custom resistance value. However, availability does not prove suitability. The designer must first check that the standard component will allow the circuit to function as intended.

This can influence the design itself: it may be sensible to adapt a design to use standard components, provided that the adaptation does not compromise its required performance.

Specialist materials: meeting requirements that standard items cannot

Specialist materials and components are selected for particular technical requirements. They may need to come from a specialist supplier or be specially ordered; some are custom-made or non-standard.

Their advantage is that they can meet a need that an ordinary stock item cannot. Their disadvantage is that obtaining them may take longer and cost more. A designer must therefore identify these needs early enough to allow for ordering and delivery.

Suppose a system needs a component with a characteristic that the available standard range cannot provide. Choosing a stock substitute simply because it arrives sooner could leave the system unable to perform its intended function. In that case, the specialist component may be justified, but the production schedule must allow for its longer lead time.

The decision is not ‘stock is good, specialist is bad’. It is whether the specialist requirement is necessary and whether its supply can be managed reliably.

Scarce elements can limit component supply

Some components depend on scarce elements. Examples include cobalt used in some batteries and neodymium used in magnets in speakers.

Scarcity is not only about how much of an element exists. Supply can also be vulnerable when extraction or production is concentrated in particular geographical areas. A disruption affecting those sources can make the element harder to obtain.

The effect passes along the supply chain: limited access to an element can restrict the manufacture of components containing it, leaving product manufacturers facing shortages or longer waits. Thus, a designer may be able to buy a finished component today but still need to consider whether it will remain available throughout production.

Making a justified selection

For a speaker, a designer might value the performance provided by a neodymium magnet while also recognising the supply risk associated with the element. An alternative is worth considering, but only if it still meets the speaker’s requirements.

A sound selection therefore asks three connected questions: Does the component do the job? Can it be obtained in the required quantity and time? How dependable is its future supply? Stock items are often the practical choice where they meet the requirements; specialist items may be necessary for particular performance needs; reliance on scarce elements requires attention to supply risk.