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Here we learn about hot wire anemometer, Hot Film anemometer, and it’s advantages and disadvantages. Hot wire Anemometer : ~ Hot wire anemometer is used for measurement of flow rate of fluctuating and unsteady flow. ~ A sensor of 5 micron diameter platinum tungsten wire welded between two prongs of the probe and heated electrically to form part of Wheatstone circuiit. ~ When the probe in introduced into the flowing fluid, it tends to be cooled by the velocity and there is decrease in its resistance. ~ The rate of cooling of wire depends upon the: (i) Dimension and physical properties of the wire. (ii) Difference of the temperature between the wire and fluid. (ii) Physical properties of the fluid. (iv) Stream velocity under measurement. ~ There are two methods of measuring fluid flow. Fig. Hot wire bridge circuits. 1. Constant-current mode : ~ Fig 4.3.1 (a) shows Constant-current mode hot wire anemometer in which the voltage across the bridge is kept constant. ~ Initially the circuit ad...

Here we learn about Sling psychrometer, and their advantages of sling psychrometer with fig., Hair hygrometer, recording psychrometer. A ) Sling psychrometer : ~ The sling psychrometer consists of handle of two mercury thermometers mounted on frame, which has handle provided for rotation of psychrometer as shown in Fig. 5.2.2. ~ For accurate measurement temperature, it is an essential condition that the air should move with velocity around the wet wick. ~ The sling psychrometer is a specific form of wet and dry bulb psychrometer. ~ It uses glass thermometers in a frame designed to be swing rapidly to obtain adequate air velocity. ~ This is suitable for measurement in the range of- 0 to 100 % RH. Fig. Sling psychrometer Applications of sling psychrometer : For setting and checking hair hydrometer. For routine meteorological observations. B) Hair hygrometer : ~ Hair hygrometer is the simplest and oldest type of hygrometer. ~ It is made using hair as shown in Fig. 5.2.1. ~ Human hair leng...

Here we learn about load cell, Definition of load cell, Advantages of load cell and Disadvantages of load cell, Application and types of load cell. Load Cell : Definition of load cell : Fig. Strain gauge load cell ~ Load cell is a force transducer which utilizes deflection of an elastic member as a primary sensing device and strain gauge as a secondary transducer. In hydraulic and pneumatic load cells, fluid pressure is used to measure the force.     Types of mechanical load cells : 1. Hydraulic load cell 2. Pneumatic load cell 3. Strain gauge load cell Applications of load cell : Tool dynamometers, weighing machines for vehicles, load measurement in material handling devices such as crane or AGV. Bag filling machines, suspension bridges etc. ~ Load cell is application of wire type bonded strain gauge. ~ It works on the principle of the elasticity i.e. when axial force is applied, its column gets compressed and when force is released it regains its original position. ~ Four wi...

Here we learn about Strain Gauge Rosettes with diagram Strain Gauge Rosettes ~ Multiple grid or rosettes are a group of gauges bonded to the same supporting material in definite relative positive. ~ When two 0r more grid elements are configured in a definite fashion for use at one point, then it is called a strain gauge rosette. In the use of a single element gauges, the orientation is a critical factor and are useful only in known directions. ~ But, with the use of strain gauge rosettes, there is no restriction on the orientation and can be used to measure stress whose magnitude and direction are totally unknown. ~ Theoretically, it is possible  calculate all the desired information when a 3-gauge rosette is used for measurement at a point. The different types of strain gauge rosettes are shown in Fig. 5.6.7. ~ Depending upon the arrangement of the grids, we have the rectangular, delta and T delta rosettes. Resistances Heating ~ When a resistance R carries a current I for t second...

Here we learn about Closed loop system, Definition, Advantages and disadvantages of closed loop system, Examples of closed Loop system. Closed Loop System Definition of closed Loop system : ~ A system in which the controlling action is some how dependent on the output is called as closed loop system. ~ Such system uses a feedback that is part of the output is feedback to the input and it is compared with the reference input. ~ Feedback is the property of the control system which allows the output to be compared with the reference input so that appropriate controlling action can be executed. ~ It is then compared with the reference input giving error signal e= R ± b. When feedback signal sign is positive, system is called as, positive feedback system (e = R+ b) and when feedback sign is negative system is called as negative feedback system (e= R-b). ~ This error is then manipulated by the controller generating manipulated actuating signal for the process to be controlled. This manipulat...

Servomotor Mechanism : ~ By servo-mechanism or simply a servo, we mean , system which is used to automatically control the output mechanical position, or time derivative of position, viz velocity or acceleration of the output member, in response to variations of input signal. ~ As such, a servo system is used to position a final control element in a generalized instrumentation system. ~ Servo-mechanism has found number of applications in industry, such as in tool position control, radar tracking systems, misslle guidance system etc. ~ Actuators are used to operate the final control element such as a valve, heater, etc. It is an important element of servo-mechanism.  A servo-mechanisin is a closed loop system that moves or changes the position of the controlled object so that it agrees with the position of a control device. In short servo may be considered, as any type of closed-loop system. ~ The error detector compares the feedback signal with the reference input or command and ge...