Evaluation (Validation and Verification) - Medical Device Design: Innovation from Concept to Market - page 221

saturation
curve

o/p

i/p

range

Figure 9.7
Range.

o/p

o/p

do

FSD

i/p i/p

Figure 9.8
Repeatability: (a) good repeatability; (b) poor repeatability.

Repeatability is defined as the largest variation in output (indicated by the small arrow), do , as
a percentage of full scale deflection. Full scale deflection (FSD) is the largest possible output
over the range of the device. Hence

do
FSD

R

e

×100%

(9.2)

9.3.3.4 Reproducibility
Reproducibility is similar to repeatability, but in this case others conduct the repeat
experiments. The calibration is conducted in a similar manner, using similar protocols, but
different people use the device in different situations (e.g., different hospitals) ( Figure 9.9 ).

Reproducibility is defined similarly to repeatability:

do
FSD

R 100% (9.3)

o

9.3.3.5 Resolution
Resolution is defined as the smallest change in input that creates a discernible change in output.
It is akin to comparing two people walking down a road, one being very tall, and the other very
short. Both cover the same distance, but the shorter chap does it in smaller steps. Hence if your
device uses a rule to measure distance then its resolution is the smallest division.

Since we all went digital, resolution has become extremely important. Systems use analog to
digital converters (ADCs) to change continuous analog signals into a simple stream of numbers.
However the resolution of an ADC depends on the range of the input and the number of bits.