1 Sensor and Transducers

Sensor and Transducer

1.1 Typical Instrumentation System

Figure 01. Typical  instrumentation system Block Diagram.

• Element of Typical instrument system

1. Primary sensing element
2. Variable conversion element
3. Variable manipulation element
4. Data transmission element
5. Data presentation element

Let see one by one:-

1. Primary sensing element:-The primary sensing element is also called as sensor. Normally transducers are used as a primary sensing element. In this section, the physical quantity (such as temperature,flow, pressure,etc.) are sensed and then converted into analogues signal.These are Primary transducer.
2.  Variable conversion element:-It converts the output of primary sensing element into suitable form without changing information. Basically these are secondary transducers.
3. Variable manipulation element:-The output of transducer may be electrical signal i.e. voltage, current or other electrical parameter such as resistance, inductunce etc. Here, manipulation means change in numerical value of signal. This element is used to convert the signal into suitable range. (Normally 4-20 mA current used to take sensor output)
4. Data transmission element:- Most of the time direct reading of the quality at a particular place can not be shown or not accessible  (Example – Measurement of temperature in the Boiler). In particular a case, the data should transfer from one place to another place through channel which is known as data transmission element. normally transmission path are pneumatic pipe, electrical cable and radio links.  The electronic instrumentation system where radio link is used called as telemetry system.
5. Data presentation element:-Finally the output is stored or given to the controller to perform specified action. As per user demand it performs different functions like indicating, recording or controlling.

1.2 Pressure Gauge Instrumentation System:-

Figure 02. Pressure Gauge.

Figure 03. Pressure Gauge Construction .

Figure 04. Pressure Gauge Instrumentation System .

Working of Pressure Gauge (Bourdon tube) 

1. As the pressure is applied at the fixed end i.e. stationary socket free end undergoes deformation.

2. The free end is connected to  sector which is attached with the pinion on which pointer is fixed.

3. Hence according to Pressure applied at stationary socket , pointer position  is transferred to pointer via this mechanism.

4. This will result into deflection of pointer and indicate the pressure reading on calibrated dial.

Advantages of Bourdon Gauges 

1.         Simple Design
2.          Inexpensive
3.          High-pressure range
4.          Good accuracy except at low pressure.
5.          It can be easily used with electrical devices like LVDT.

Disadvantages of Bourdon Gauges.

1.           Susceptible to shock and vibration
2.          Gauges are subjected to hysteresis

Application of Pressure Gauges.

1.          To measure liquid/gas pressure