1. MEASUREMENT OF SPEED AND HUMIDITY
SESSION - 6
MEASUREMENT OF SPEED AND HUMIDITY

2. SPEED
Linear speed is the speed with which the body moves in the linear path.
Speed is the scalar quantity.
It is how fast an object is moving.
It doesn't have a direction.

3. SPEED
Units for linear Speed The SI units for speed are m / s (meters per second). In everyday usage, kilometers per hour or miles per hour are the common units of speed. At sea, knots or nautical miles per hour is a common speed.

4. SPEED Rotational Speed
Rotational speed or angular speed is the number of revolutions over a unit of time for an object travelling in a circular path.
The angular speed of a rotating object usually expressed in radians per second (rad/s) or revolutions per minute (rpm).

5. SPEED
Measurement of rotational speed has acquired prominence compared to the measurement of linear speed. Linear Speed Formula in terms of angular speed is given by: linear speed = ω*r Where, ω is angular speed and r is the radius of circular path.

6. SPEED
Linear Speed Formula in terms of angular speed is given by linear speed = ω*r Where, ω is angular speed and r is the radius of circular path.

7. SPEED
“An instrument used to measure angular speed as of shaft is known as tachometer.”
Tachometers may be broadly classified into two categories:
Mechanical tachometers and
Electrical tachometers.

8. SPEED Mechanical tachometers:
These tachometers employ only mechanical parts and mechanical movements for the measurement of speed.

12. Centrifugal tachometers
The device operates on the principle that centrifugal force is proportional to the speed of rotation. Two flyballs (small weights) are arranged about a central spindle. Centrifugal force developed by these rotating balls works to compress the spring as a function of rotational speed. A grooved collar or sleeve attached to the free end of the spring then slides on the spindle and its position can be calibrated in terms of the shaft speed.

13. Centrifugal tachometers
Through a series of linkages, the motion of the sleeve is usually amplified and communicated to the pointer of the instrument to indicate speed. Certain attachments can be mounted onto the spindle to use these tachometers for the measurement of linear speed.

14. Electrical tachometers
An electrical tachometer depends for its indications upon an electrical signal generated in proportion to the rotational speed of the shaft. Depending on the type of the transducer, electrical tachometers have been constructed in a variety of different designs.

17. Drug cup tachometer
In an eddy current or drag type tachometer, the test shaft rotates a permanent magnet and this induces eddy currents in a drag cup or disc held close to the magnet. The eddy currents produce a torque which rotates the cup against the torque of a spiral spring. The disc turns in the direction of the rotating magnetic field until the torque developed equals that of the spring. A pointer attached to the cup indicates the rotational speed on a calibrated scale.

18. The automobile speedometers operate on this principle and measure the angular speed of the wheels. The rotational measurement is subsequently converted into linear measurement by assuming some average diameter of the wheel, and the scale is directly calibrated in linear speed units. Eddy current tachometers are used for measuring rotational speeds upto 12,000 rpm with an accuracy of ±3%.

19. Applications of tachometers
Centrifuges
Saw blades
Grinders
Elevators/escalators
Engines
Motors
Conveyor belts
Fans
Propellers

24. Humidity
Liquid in the Air

25. Humidity is: A measure of the amount of liquid in the air
liquid is added to the air by the process of EVAPORATION.

26. Relative Humidity
RELATIVE HUMIDITY is the amount of liquid in the air compared to the amount of liquid the air could possibly hold.
Humidity values are usually given as Relative Humidity.
Examples:
if the air is holding half the liquid it could hold, it’s Relative Humidity is 50%.
If the air is holding ALL the liquid it can hold it is saturated and the relative humidity is 100%
If the air is holding no liquid, relative humidity is 0%
If it holding a quarter of the liquid it could hold, 25%

27. Absolute Humidity
ABSOLUTE HUMIDITY is (expressed as grams of water vapor per cubic meter volume of air) is a measure of the actual amount of water vapour (moisture) in the air, regardless of the air temperature.

28. What temperature can hold more liquid vapor?

29. Factors that Affect Relative Humidity
Amount of liquid: If you increase the amount of liquid in the air (by adding it due to evaporation), Relative humidity will go up.
Temperature: Since warm air can hold more liquid than cold air, if you lower the temperature the Relative Humidity will go up, even if you don’t add more liquid.

30. liquid capacity of air at different temperatures

32. Measuring Humidity Relative Humidity is measured using a PSYCHROMETER.
A psychrometer is made of two thermometers. One is covered with a wet cloth. When air moves over the wet cloth, evaporation occurs and lowers the temperature on that thermometer.
If you compare the temperature on the two thermometers you can get the relative humidity.

35. Ex. 1
Dry Bulb = 14 degrees C
Wet Bulb = 10 degrees C
Difference is = 4
1st – look at dry bulb reading (14)
2nd – find difference (4)
3rd – RH is where they meet = 60%