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Jul 16th 2013

Why and How Should You Perform a Feasibility Study?

The first things to understand about feasibility studies are there purpose and the importance of instigating them whenever the evidence says you need to.

A feasibility study is to confirm that a design concept is realisable. To write a robust technical specification it is important to ask the question, of every clause, is this possible? I suppose that sounds like a statement of the obvious but it has to be read in context. Most people writing technical specifications or doing quotes are subject to pressures that make it difficult to be objective. If you are an engineer you usually just want to get on with it. Doing the job is exciting and an engineer usually itches to have a go. Someone doing a quote just itches to get the order. Both these pressures incline one to accepting loosely written clauses.

Consequences of ignoring feasibility: I am sure this also sounds obvious but problems from a failure to thoroughly address feasibility are remarkably common in engineering. What happens is, you soldier on with your design, make a prototype and find its performance is impaired because something you assumed was the case, isn’t. Costs to reputation and product can be frightening!

Be SMART: Any objective in a specification should pass the SMART criteria. If it doesn’t you need to either improve its description or do some feasibility work so that you have enough information.

S – specific (The screw will be tightened to 30Nm – which screw? It will be hot to the touch (How hot!))

M – measurable (The current will be 1A. What tolerance? Can you measure what you are being asked to measure with the resources available)

A – achievable (Is it possible?)

R – relevant (tight tolerances and requirements that aren’t relevant to the product just cost money – no benefit. A tolerance should never be set tighter than is required to achieve the objective)

T – time bound

So the rules for feasibility research/test work are:

1) Take the concept and write a technical specification.
2) Apply the SMART acronym to all the clauses.
3) If any fail you need to think about some feasibility research/testwork.

Examples always help with getting to grips with methods like this.

A design requirement is that a ‘widget’ fits into an enclosure 10mm x 20mm x 30mm. How do you know whether it will fit (unless it is obviously much smaller than that) unless some preliminary design is done to confirm it. Achievable?

A design requirement is that a ‘widget’ will cost less than £20. How can you be sure this is possible before doing some preliminary work (identify components and find out their cost). Achievable? Measurable before it has been designed? What quantities are required (makes a massive difference to cost)?

A design requirement is that a ‘widget’ will not cause EMI or be subject to it (known as EMC testing). How can this be confirmed at all without testing (there are lots of test houses in the UK that can do this)? It is necessary to have made some hardware to confirm this. Achievable? Measurable? You probably don’t have the equipment to measure this.

It is necessary to achieve a 15 degree aperture with an LED but it must be surface mounted on the PCB. I think you will find this is only possible with leaded LEDs. Achievable?

An audible alarm is to be used with a device (PCB mounted buzzer) and it is installed inside an angular metal frame. It is to be audible from 10m. Measurable? What about ambient noise? What about measurement of the 10m (tolerance)? What about the difference in hearing ability of different individuals? It should be a dB measurement in a controlled environment at a specified distance.

An LED is used as an alarm signal which is to be visible at 100m in bright daylight. Same issues as example above except light not sound.

A PVC cable is to routed outside and bent round a 10mm radius. Achievable – PVC goes rigid at around about 0C. it will crack. Measurable – stresses are related to rate of bend – different results depending on how quickly it is bent.

A patient’s attempt at a breathe is to be detected using pressure sensor (HCMXXXX). Measurable? What is the trigger level at which a breathe is confirmed? It should read something like ‘a pressure less than -4cmH2O will signify an attempt at a breathe has occurred).

The device (an electronic PCB) must have a serial interface that is to be used to communicate with a host PC. The software for the host is written and supported by the customer. Specific. Fair enough but what protocol. What baud rate? How many start and stop bits? What order and what data is being sent? Is there to be handshaking? Parity?

The system is to be a 75 ohm +/- 1 ohm (matched impedance). Achievable – high quality co-ax cables have characteristic impedance +/- 3 ohms. If the cable is this variable how is the requirement to be achieved?

5mm bolts will be used and they shall be tightened to 40Nm. Achievable – a rule of thumb is the correct limit for torque on a bolt is 3 times its diameter. This would damage the bolt – probably.

So a recap on the rules:

1) Take the concept and write a technical specification.
2) Apply the SMART acronym to all the clauses.
3) If any fail you need to think about some feasibility research/testwork.

Good luck with your feasibility and remember thorough feasibility results in high quality specification. If you're looking for an experienced electronic designer to conduct a feasibility study, contact Newbury Innovation now!