Testing and Calibration of Instruments

Test Measurement Instrumentation :

           Measurement is fulfilled only when you are able to express the results in numbers (understandable way) - if you measure the quantity of milk in a cup, you should be able to say it as 250 ml / 500 ml / 50 ml.....of milk is in the cup. If you say there is "கொஞ்சம் பால்", then you have not performed the measurement there.

           Measurement involves two things : Measuring unit (Test Object - is an unit / device which is used to test the object (to be measured)) and the object (parameter / physical object...)

           The performance of the Measuring unit (Test object) is expected to be same for different conditions of and to perform correctly under specified conditions.

           Measurement system involves the following.

                        1. Components.

                        2. Installation

                        3. Wiring

                        4. Calibration 

Measurement Instrumentation and Test Measurement Instrumentation :

                If the result of the measurement system is used for explaining / knowing the condition of the environment / process then that is known as Measurement Instrumentation.

               If the result of the measurement system is used to verify whether the product is working against the specification and to monitor the operation of equipment (operation means not only checking whether it is working or not, but also working under different relevant conditions), then that is known as Test Measurement Instrumentation.

                 R&D labs

                 Product development / design centres

                 Manufacturing plants

                 Maintenance facilities

                 Commercial and Household products - are the places where the test measurement instrumentation is used.

Components of Test Measurement (TM) System:

                        Sensor / Transducer (Input)

                        Signal conditioning system (Conditioning and Transmission)

                        Display, Data logger, Data Acquisition system, Data Analyzer (Output)

Characteristics of an ideal TM System:

           Even though it's a whole system of individual components, the performance of the system is based mostly on the character of the transducer / sensor. Because, this component only has direct contact with the process / environment of the process. 

            * small size and low mass

            * immune to environmental changes

            * wide range of operation (reduces the no. of sensors to be installed - reduces the space)

            * high accuracy (reduces the measurement uncertainity)

            * good linearity (improves rangeability and accuracy)

            * wide frequency response

            * low cost

            * ruggedness

            * ease of operation

Invasive and Non invasive measurement system (contact and non-contact transducers /sensors with process or test system)

Test Measurement Instrumentation and Process Instrumentation - for laboratory purpose and Field purpose respectively - in general

         these are distinguished by

                       the place of use (lab or industry)

                       the size (small or heavy)

                       the application (specific or wide range)

                       the frequency response (high or static to low)

                       stability (less or more)

                       ruggedness (less or more)

                       accuracy (high or low)

                       price (high or low)

                       environmental range (wide or limited)

                       use of signal conditioning unit (separate unit or self contained)

                       sensor as transducer or sensor as transmitter.