Electronics Made Easy - a Complete Introduction to Electronics - Martin Denny [16]
a) Signal input limits where applicable.
b) Power Supply requirements including maximum and minimum working voltages, frequency and power factor when applicable. This should also include current loading.
c) Environmental Conditions, ie maximum and minimum working temperatures and storage temperatures where applicable.
d) Output Information ie accuracy, linearity, hysteresis, temperature drift, noise, maximum and minimum output levels etc.
e) User Controls, ie Gain ( or Span ), Zero, etc. These can be expressed as the voltage variation at the output or as a percentage of output.
f) Packaging Details ie box or housing, size, weight etc.
It is usual to provide an operating manual with any design, which would include this specification. The manual should also provide a description of the design philosophy, operating instructions and limitations of operation together with full circuit, layout diagrams and component lists.
The Quotation
This stage is possibly one of the most important parts of the design function, as it must be adhered to. All costs ie design, development, construction etc, must be calculated including the time span of the project ie delivery date. A suitable profit margin must also be allowed for. A quotation should include the following:
a) Description of Device
b) Specification
c) Warrantee ie how long do you take responsibility for its operation.
d) Additions ie operating manual, test certificate, declaration of conformity etc.
e) Cost and delivery, remember to include costs incurred in the development of the quotation, and allow a margin of error in the delivery time ie determine a reasonable time and double it.
In some cases part of the development and testing costs may be waived if it is considered that further units may be constructed in the future at a similar cost, or it is desirable to gain the contract from this company in order to encourage further work.
Assuming the contract is awarded to you or your company work can begin once you have received the order to start work at the agreed price. At this stage the design must be fully developed before production can begin.
Design Development
Any doubts in the design concept should be addressed at this stage, by experiment and or by consulting manufacturers data. A design analysis programme may also be of use. The initial design process should have enabled the designer to check the viability of his design but at the pre production stage many other considerations must be included in the design:
a) How many new and relatively untried components will be used in the design and what is the probable reliability of these components. The incidence of failure of older components is known therefore the larger the content of older technology in the design the more predictable the failure rate of the design, and ultimately the more reliable the design.
b) What is the effect of individual component failure within the device. Does the device fail safe. Is it necessary to alarm individual failures or provide a back-up system.
c) Is the case or housing the correct size and shape for the device. Could the appearance of the device be improved, and what colour scheme will be used for case and panels. Is it only necessary to change the colour of panels, reducing painting costs. How will panels be labelled, silk screen printing for example is only cost effective for large batch production ( 50+ ).
d) Having identified all proposed controls will they fit on the panels in a logical fashion (Ergonomics).
e) What production methods will be employed in the manufacture of the device. Will printed circuit boards be used or prototype boards. Prototype boards avoid the cost of producing and processing printed circuit board (pcb) artwork but inevitably will result in a loss of reliability and increased production time. For a rule of thumb guide it is generally cost effective to produce printed circuit boards for batches of 3 or more but individual requirements might dictate the use of a pcb for one unit ( ie reliability and strength ).
f) The panel