Inclined Tube Manometer:

Inclined tube manometer is a simple and cheap instrument that is commonly  used for measuring differential pressure in a mine.  It  resembles to a U-tube Manometer. One limb is a tube of uniform bore (6 mm internal diameter) which is kept inclined at a low angle to the horizontal line. The other limb is  transformed to a large reservoir with cross-sectional area 300-400 times larger than that of the cross-sectional area of inclined limb. Any change in the level of manometer fluid in the reservoir can be neglected in comparison with the change in fluid level in the inclined tube.  Hence, a scale along the inclined limb directly reads pressure difference.

For greater sensitivity, the inclined tube manometers can be filled with alcohol which also gives better meniscus than water. The instrument can be made suitable to measure a wide range of pressures by changing the inclination of tube. Smaller angle of inclination can be used for measuring lower range of pressures.

For the further study on manometers the following aslo can be referred:

1.Curved-tube manometer

2. Two liquid differential manometer

3.Tilting micromanometer

Askania Minimeter:

This instrument consists of two inter-communicating containers filled with distilled water. Container f is the observation vessel and N is the balancing vessel. L is the nipple for connecting to the high pressure side and D , to the low pressure side. Vessel N can be raised or lowered by operating the knurled ring P, the amount of movement being noted on the scale r graduated in millimetres and the micrometer scale S having a least count of 0.01 mm.

At the outset the central point of nipple D is brought to the zero of the scale R by turning of the knurled ring P. Cock E is opened and vessel F is filled with water till the pointer G just touches the water level. E is then closed. The pointer is brought to touch the water level exactly by an adjustment of the mild head H, the exact coincidence being observed through the lens K.

The two nipples are then connected to the pressure lines when the level of water in F falls and that in N rises. Now the vessel N is raised turning the knurled ring P until the water level in F again touches the tip of the pointer  G ( null point ). The readings on the scale R and the micrometer S then give the pressure in mm.

 

 Measurement of Pressure:

Though pressure is an absolute quantity, every measurement is made relative to reference like ambient air pressure.

1.  Absolute Pressure: is referenced to zero(0) against perfect vacuum ( = gauge pressure + atmospheric pressure )

2.  Gauge Pressure: is taken in reference with ambient air pressure.

3.  Differential Pressure: is the difference in pressure between two points.