Generalized measurement system: block diagram, elements, stages, example.

Generalized measurement system

The generalized measurement system is a set of elements in which the measurement process is carried on by the system.  There are many measuring instruments, but they exist for measuring some values of some variables. In some measuring instruments, the measuring process is done easily, and finally, it gives the output for the input as reading or signal based on the magnitude of the input variable.

For example, the measuring process in some simple instruments is easy and simple (for measuring length, mass, etc). Most of the instruments like indicating thermometer undergo a  complex measuring system. There will be each element for each function in these complex measuring instruments.

Block diagram of the generalized measurement system

Let’s see about these elements one by one in this article. The blocks in the block diagram represent each element in the generalized measurement system.

Block diagram of the generalized measurement system
Block diagram of the generalized measurement system

Elements of generalized measurement system

The elements of the measurement system are listed below,

  • Input variables
  • Primary sensing element
  • Variable conversion element
  • Variable manipulation element
  • Data transmission element
  • Data processing element
  • Data presentation element
  • Observer

Input variables

Input variables may be any unknown variable. Without any input variables, the final result can not be achieved by the system.

Inputs should be in a certain amount of measured quantity.
 

Primary sensing element

The first element of the measurement system is the primary sensing element. The main function of the primary sensing element is to sense the input variable and gives the output according to the measurand.

This output will be the input of the next element. So this output is converted analogous electrical signal. This is achieved by using transducers.

Variable conversion element

It receives the output of the primary sensing element as input. As the name indicates, the conversion of the variable from one form to another form takes place. The conversion process is done without altering any data contained in the input. 

The requirement of this element depends upon the measuring instruments, some may need and some may not because they are converted into a required form in the previous element (primary sensing element). 

Variable manipulation element

This element manipulates the input variable.

As per required magnification, the variables are manipulated by manipulation otherwise called as amplification. This is done for the required output from the input variable.

The manipulation process does not depend upon the variable conversion element, so the manipulation of variables can proceed directly without any conversion element in some cases.

Data transmission element

Transmission of data or information from one element to another element takes place in this data transmission element. Data transmission is the main function of this element.

Data transmission elements such as data cables, transmitters, and receivers, transmission shafts, etc are used to transmit the data from one element to another element.

Data processing element

Data is modified and processed before the final result comes. The data processing element modifies the data for some reasons like,

  1. Modification for final output form,
  2. Modification for some final calculations,
  3. Modification for errors in the instruments such as positive error, negative error, zero error, temperature error, etc.

For the following reasons, the data processing element is used in all measurement systems.

Data presentation element

Finally, data is present to the observer via the data presentation element. The presentation element is such as to monitor, recorders, needle pointers, LCD and LED display, alarms, indicators like the analog indicator and digital indicator, etc. Without data presentation element, data cannot be delivered to the observer.

Observer

The measurement data is finally delivered to the observer via the data presentation element, for further clarification and calculation. The observer used to record these data for further clarification in the future. The recorded data are stored either in hard copy or digital copy.

Stages in the generalized measurement system

Stages in the generalized measurement system
Stages in the generalized measurement system

There are four stages in the generalized measurement system, they are listed below

  1. Sensing stage
  2. Conversion stage
  3. Manipulation stage
  4. Recording stage

Sensing stage

The sensing stage is the primary stage. The input variables are sensed by the sensitive sensors in the variable sensing element and converted to the required type of signals.

Conversion stage

The conversion stage is the second stage. This stage is not required for some instruments because already been done in the sensing stage.

Other instruments are passed through this stage for further conversion of signals.

Manipulation stage

This stage is the tertiary stage. The signals are further manipulated or amplified for the final stage. Manipulation is done for the signals to indicate by the final stage.

Recording stage

This is the final stage. In this stage, the manipulated signals which contain data, are transmitted through the data transmission element to the data presentation element. The data presentation element delivers the data to the observer via a monitor, recorders, alarms, pointers, led and LCD screens, etc. The observer records the data and saved further clarification and analysis. By this, the recording stage ends.

Example of a Generalized measurement system

Let’s see some examples of a generalized measurement system. Some instruments like the bourdon thermometer and bourdon tube pressure gauge are built with these set of standard elements to measure their input variable. Let’s see how it works.

Bourdon Thermometer

Example of a Generalized measurement system
Example of a Generalized measurement system

Like an ordinary thermometer, a bourdon thermometer is also used to measure the temperature. This thermometer is constructed with some parts like a sensing bulb, capillary tube, bourdon tube, bimetallic strip, and finally pointers.

Example of a Generalized measurement system
Example of a Generalized measurement system

This block diagram shows the working principle of the bourdon thermometer. When the thermometer is placed in the hot or cold body, the sensing blub senses the temperature of the body. This is the sensing stage. This causes a displacement of sensing fluid through the capillary tube in the thermometer. The displacement of the fluid and the body temperature are proportional to each other.

Next, the conversion stage starts. The fluid is displaced to the bourdon tube, where the conversion process occurs. The fluid displacement is converted to link displacement.

This link displacement is amplified to get the exact result. This amplification is done by gears attached to the pointer and the link. Finally, the output is indicated by the deflection or movement of the pointer.

Bourdon tube pressure gauge

Example of a Generalized measurement system
Example of a Generalized measurement system

The construction of a bourdon tube pressure gauge is similar to the bourdon dial thermometer. And also the working principle is the same. The main difference between these two instruments is the measuring variables.

When the gauge is fitted to the pressure source, the internal pressure in the tube gets raised and the displacement occurs. This displacement is manipulated by rack and pinion gears to get the exact output value.