The Generalized Measurement system
1. The Generalized Measurement system¶
The schematic above is representative of many measurement systems used for research, process improvement and optimization, process control etc. In order to design a measurement system to suit our purposes, we first need to address some basic concepts and definitions.
Measurement - The process of assigning a numerical value to an observable.
This suggests that we first need to clearly identify what we aim to observe and wh can measure. Often, the process of measuring will involve some mathematical operation to extract the physical parameter of interest. For example, consider a simple tensile test. Your objective is to find the material’s Young’s modulus. Obviously, this is not a direct measurement. Instead you measure forces and displacements which in turn will be converted to stresses and strains from which the value of the Young’s modulus will be calculated.
The generalized measurement system is composed of:
Sensing element - a physical quantity of interest will be detected and converted into an electrical signal. Examples are a strain gauge, a temperature sensor (e.h. a thermocouple) , a camera etc. We will later on differentiate between a sensor and a transducer, in many systems, the sensing element is in fact a combination of the two.
A conversation element - In many cases, the output of the sensing element will need to be manipulated such that it will be useful for the following steps of the measurement. and Analog to Digital conversion is often use to allow our signal to be conditioned and recorded .
Signal manipulation - processes such as filtering, amplification and attenuation immediately come to mind. We may also encounter situations in which we wish to agglomerate our signal over time and only transfer an integrated form of it or a derivative. In other cased we may wish to enhance the user’s ability of viewing the signal (e.g. a sector and pinion for increasing the pointer movement in a mechanical gaging element such as a Bourdon-tube pressure gage).
Data storage - we will usually need to keep record of our measurements and thus require a systems for recording the signal. The choice of storage may in some cases be no less important than the sensing element and signal conditioning stage.