Preliminary conception

Once the concept is defined and chosen, the engineer proceeds to the preliminary design stage, also known as preliminary engineering, during which the design parameters are optimized according to the objectives and needs of the customer. In complex cases, the preliminary engineering is divided into progressive precision stages. It is imperative to document not only the calculations and the results themselves, but also to explain the logical flow of the design.

Preliminary and detailed design

At this stage, the engineer must take care to perform the following main actions:

• The basis of the design
• Calculations
• Plans
• Interdisciplinary co-ordination
• The design review
• The preliminary engineering report

Basic design

The engineer subdivides the design into enough elements to achieve the degree of precision required by the terms of reference and the project. It determines the value of the parameters of each design element based on calculations, simulations, tests, measurements, and so on.

The engineer takes particular care not to neglect major elements and makes sure to explain the logical progression of the design of each element and their interactions.

Calculations

If necessary, the engineer organizes the calculations in an explicit form to facilitate understanding and interpretation. It can, for example, group them by themes or variables.

The engineer can then make sure more easily that the calculations are complete and valid and that the logic is respected. If a statistical method is used to eliminate doubtful results or other processing operations are applied, the engineer must explain them and justify their need.

The calculations include all the documents that allow them to be reconstructed (references, characteristic curves, basic data, estimates, standard articles or codes, etc.).

The engineer checks the validity of the means he uses to make his calculations, for example, by performing one or more manual calculations or by inquiring about the rigor and technical quality of the software used, if any. It assumes, of course, the responsibility for the errors that may ensue.

When the calculations are completed, the engineer should carry out a verification of their rigor and the relevance of the data used. An audit by another engineer with the required skills and knowledge may be required. Different situations require the work of an engineer to be checked by another engineer. These situations may be the following: customer requirements, the requirements of the company's quality procedures, or the complexity of the project.

Maps

The result of a preliminary design usually results in its graphic representation in the form of plans or drawings. Are considered as plans or drawings:

• Flow patterns
• Printed circuit maps
• Programming block diagrams
• Logical control diagrams
• General arrangements
• The implementation of the works

Any other form of illustration incorporating design elements.

The level of detail of the preliminary plans is limited to illustrate most of the design.

The engineer establishes and maintains a list of plans and summary content for each, including the version history.

Interdisciplinary coordination

In the case where several professionals or fields are selected for the same project, the engineer ensures that a person is designated to perform the interdisciplinary coordination. This coordination includes the final coordination of the plans.

Design Review

Depending on the situation, this step usually takes place when:

• Several areas were involved in the design
• The level of complexity requires it
• The client requests it
• The quality control procedures of the company require it.

The objective is to allow the pooling of various opinions on particular elements and to ensure their integration.

Preliminary engineering report

The engineer ensures that changes to the design review have been taken into account through a system of revisions, which may take the form of quality control procedures.

The engineer produces a final version of the preliminary engineering report with plans and, generally, a preliminary estimate of completion costs and deadlines. This allows the client to make an informed decision regarding the continuation of the project.

The plans are marked "Draft - issued for comment". It is also recommended to indicate on the plans that they are not intended or not to be used for construction, installation or manufacturing, as the case may be.

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