2.Pressure Measurement-Manometers

 

Pressure Measurement-Manometers

There are three types of Manometer which are explained below.

1) Open U-type Manometer: Manometers are working on the principle of hydrostatic balancing.

Manometer consists of a tube made of glass or other transparent material bent into the shape of a U and with both ends left open.

The force acting due to one liquid column on the same level or reference balances the force acting due to another liquid column.

Highly refined mineral seal oils of various densities are used in manometry for small pressure differences.

For higher pressure ranges mercury is used.

Water is not generally used because it evaporates, leaves a lime deposit on the tube wall

Since the pressure acting on the liquid column it will form a meniscus, When the meniscus is concave, the liquid column should be measured to the bottom of the meniscus.

When the meniscus is convex, the column should be measured to the top of the meniscus.

Accuracy of Manometer:

Accuracy is not affected by the shape or size of the tube.

Manometer liquid used could affect the accuracy of the Measurement.

When high specific- gravity liquids are used to measure extremely small pressures, the following are important variables affect the accuracy:

Density.

Vapor pressure.

Temperature.


2) Well type of Manometer: The left-hand limb is replaced by a reservoir or well which has an area much larger than the area.

This operates on the principle of Pascal law.

Pressure to be measured is applied on the well side and the reference pressure is applied on other side.

It is mainly used in laboratory and industrial purposes.

3) Inclined Manometer: It has one limb that is inclined at an angle to the horizontal plane and a vertical limb that consists of a relatively large well. The sloping tube carries a scale adjacent to it. Inclined tube is used to achieve a longer scale than the ordinary U-tube manometer for the same pressure differentials.

Advantages of manometers with respect to other inst.

1. Range is ± 30 inch of Hg.

2. Suitable for very low pressure Measurement.

3. The liquid is physically visual.

Disadvantages:

1. Bulky, size is big.

2. Glass tube is fragile so it is not recommended for field use.

3. Accuracy of the instrument is depending up to the temperature and other factors, which cannot maintain in field.

4. Mercury used in manometer make mercury oxide, which is poisonous.

5. Manometers are not suitable for high pressure Measurement and high temperature pressure Measurement.

6. Manometer’s liquid may react with the process liquid.





Comments

Post a Comment

Popular posts from this blog

1.Introduction to PLC

Image
  Introduction This knowledge is meant to supply you with basic information on PLC . Control engineering has evolved over time. In the past humans were the main method for controlling a system. More recently electricity has been used for control and early electrical control was based on relays. These relays allow power to be switched on and off without a mechanical switch. It is common to use relays to make simple logical control decisions.  The development of low cost computer has brought the most recent revolution, the Programmable Logic Controller (PLC). The advent of the PLC began in the 1970s, and has become the most common choice for manufacturing controls. PLCs have been gaining popularity on the factory floor and will probably remain predominant for some time to come. Most of this is because of the advantages they offer. ·            Cost effective for controlling complex systems. ·          Flexib...
Read more

5.UP Counter, DOWN Counter, Up-Down Counter

Image
  UP COUNTER(CTU) CTU stands for Count Up Timer, which is a type of electronic timer used to count the number of events that occur and display the result. In a CTU timer, the count value increases by one each time a triggering event occurs, and the timer counts up to a preset maximum value before resetting to zero and starting again. A CTU timer typically consists of a register to store the current count value and a clock input to trigger the counting process. When the clock signal is applied, the counter increments the current count value by one. The new count value is then stored in the register, and the output device such as a display or computer interface displays the current count value. For example, a CTU timer might be used in a factory to count the number of products that pass through a conveyor belt. The CTU timer can be triggered by a sensor detecting the presence of the product, and once the CTU counter reaches the preset maximum value, it can generate an output si...
Read more