Chapter 12 Prototyping and Testing Design of Biomedical Devices and Systems By Paul H. King Richard C. Fries

Prototyping  Hardware Easily modified and extensible model of a system, including location of individual hardware components. Easily modified and extensible model of a system, including location of individual hardware components.  Software Easily modified and extensible model (representation, simulation or demonstration) of a planned software system, likely including its interface and input/ output functionality. Easily modified and extensible model (representation, simulation or demonstration) of a planned software system, likely including its interface and input/ output functionality.

Prototyping: Hardware  Present to customers for reaction to design Size correct for application? Size correct for application? Components placed for ease of use? Components placed for ease of use?  Wood, foam, cardboard

Prototyping: Software  Sometimes used to precede hardware models  Functioning example of final product  Determines if it satisfies the customer’s needs early in process  Allow testing of changes in processes prior to actual implementation of changes

A set of screens that provide a dynamic, computerized, working model of the planned system A throw-away prototype used to clarify project goals, to identify requirements, to examine alternative designs, or to investigate a large and complex system A prototype used to validate system specifications An iterative prototype that is progressively refined until it becomes the final system A prototype that models many features but with little detail; a horizontal slice of a system’s structure chart from the top down to a specific depth most useful in the early stages of design A prototype that models few features but with much detail; a vertical slice of a system’s structure chart from top to bottom; most useful in the later stages of design A prototype that is horizontal down to a particular level, then vertical below that point A prototype of the entire system; an expanded horizontal prototype that models a greater number of features and covers multiple levels of the system’s structure chart A prototype of a single usability-critical system component; a vertical prototype that is focused on one feature Prototypes: Types LLLLow-Fidelity HHHHigh-Fidelity EEEExploratory EEEExperimental OOOOperational HHHHorizontal VVVVertical DDDDiagonal GGGGlobal LLLLocal A set of drawings (e.g., storyboard) that provide a static, non-computerized, non-working mock-up of user interface for the planned system

Prototype: Process  Build low-fidelity prototype  Re-specify, re-design, re-evaluate  Freeze these specifications  Finish building the product

Testing  Subjecting a device to conditions that indicate its weaknesses, behavior characteristics, and modes of failure.  Ultimate goal: satisfied customer

Testing: 3 Basic Reasons  Basic Information Includes vendor evaluation, vendor comparison, and component limitability Includes vendor evaluation, vendor comparison, and component limitability  Verification Process of evaluating the products of a given phase to correctness and consistency with respect to the products and standards provided as input to that phase Process of evaluating the products of a given phase to correctness and consistency with respect to the products and standards provided as input to that phase  Validation Process of evaluating a product to ensure compliance with specified and implied requirements Process of evaluating a product to ensure compliance with specified and implied requirements

Testing: Defined  Establishing confidence that a device does what it is supposed to do  The process of operating a device with the intent of finding errors  Detecting specification errors and deviations from the specification  Verifying that a system satisfies its specified requirements or identifying differences between expected and actual results  The process of operating a device or component under specified conditions, observing or recording the results, and making an evaluation of some aspect of the system or component

Test: Types  Verification  Validation  Black Box  White Box  Hardware Testing  Software Testing  Functional Testing  Robustness Testing  Stress Testing  Safety Testing  Regression Testing

Stress Testing  Designed to ascertain how the product reacts to a condition in which the amount or rate of data exceeds the amount or rate expected.  Help determine margin of safety that exists  Include Duration and Worst Case Scenario

Black Box  Verifies that the end-user requirements are met from the end-user’s point of view  Performed without any knowledge of internal structure  Tester is only interested in finding circumstances in which the device or program does not behave according to its specification.

Determining Sample Size and Test Length  MTBF (Mean Time Between Failure) Basic measure of reliability for repairable items Basic measure of reliability for repairable items  (sample size)(test time) = MTBF goal (X 2 α;2r+2 )/2  Example: Calculate the test time for a device that has an estimated MTBF of 20 per million hours if you have only fifteen units to test. List your assumptions.