UNIT-3 PRESSURE MEASUREMENT RAISED WELL MANOMETER (ENLARGED LEG MANOMETER)

As the liquid displaces the float also changes its position which is indicated by the pointer and scale arrangements P1-P2 = ρm h(1+a/A)

MANOMETER WITH SEAL POTS

INCLINED TUBE MANOMETER

RING BALANCE MANOMETER

MICROMETER

ELASTIC TYPE PRESSURE MEASURING DEVICE BOURDON TUBE 3 Types 1. C type 2. Spiral type 3. Helical type BELLOWS DIAPHRAGMS 1.Flat type 2. Corrugated type 3. Capsule type a) Convex type b) Nested type

Brass, Alloy steel, Stainlesssteel,Bronze MATERIALS USED Brass, Alloy steel, Stainlesssteel,Bronze Phosphor Bronze, Berillium copper, Monel and Nickel FACTORS TO BE CONSIDERED FOR BOURDON TUEB Sensitivity, Non-linearity,Hysterisis,Static errors, Elevation errors,Response time, Power rating,Torque gradient constant.

BOURDON TUBE C-TYPE

Displacement of tip is a = 0.05ap/E (r/t)0.2(x/y)0.33(x/t)3 a-Cross sectional area p-Pressure applied t-Thickness of tube E- Modulus of elasticity

SPIRAL TYPE

HELIX TYPE

High over range capability and ratio is 10:1 HELIX TYPE ADVANTAGES It is stable for fluctuating pressure and it is adaptable for high pressure. High over range capability and ratio is 10:1 By increasing the number of helical coil we can increase the range of the pressure to be measured.

BELLOWS

BELLOWS The displacment of bellow element is given by d= 0.453pbnD21-2/Et3 p- pressure b-Radius of each corrugations n- No of semicircular corrugations D-Mean diameter -Poissions ratio E – Modulus of elasticity

SPRING LOADED BELLOW

Deflection of bellows d= pAb /kb+ks p-pressure Ab- Effective area of the bellows Kb,Ks – Stiffness constant of bellows and spring

DOUBLE BELLOW DIFFERENTIAL PRESSURE GAUGE

DISADVANTAGES 1. It is not suited for dynamic pressure measuremnt. 2. It is required temperature compensator to reduce error due to change in ambient temperature ADVANTAGES It is very suited for measuring vacuum and low pressure,medium and high pressure.

DIAPHRAGMS PRINCIPLE The pressure to be measured is applied to the diaphragms depending upon the pressure deflection occurs in the surface of the diaphragms. Deflection depends upon the thickness and diameter of the diaphragms.

DIAPHRAGMS

Pressure measurement using diaphragm

CAPSULE

ELECTRO MECHANICAL PRESSURE MEASUREMENTY (POTENTIOMETRIC TRANSDUCER)

POTENTIOMETRIC TRANSDUCER ADVANTAGES Simplicity, Ruggedness DISADVANTAGES -Longer size, poor frequency response, Problem on account of noise due to the movement of wiper.

INDUCTIVE TRANSDUCER

INDUCTIVE TRANSDUCER

Reluctance of upper = R0+k(D+d) Reluctance of lower = R0+k(D-d) If P1>p2 – diaphragm deflects downwards Reluctance of upper = R0+k(D+d) Reluctance of lower = R0+k(D-d) Inductance of the upper coil (L1) = N2/ R0+k(D+d) Inductance of the lower coil(L2) = N2/ R0+k(D-d) The bridge become unbalanced e0 = ei[ R/(R+R) - L2/(L1+L2)] e0 = ei kd/2(R0+ kD)

LVDT TRANSDUCER

LVDT TRANSDUCER ADVANTAGES 1. Good sensitivity, stiff primary sensor helps to reduce environmental effects. 2. Good frequency response, frequency greater than 0.1MHZ 3.Linearity is good for very small displacement.

DISADVANTAGES 1. Limited dynamic response 2. If displacement is high the response becomes non-linear.

STRAIN GAUGES

STRAIN GAUGES

STRAIN GAUGES ADVANTAGES 1. Good frequency response used for both static and dynamic response. 2. Good resolution even for small displacement. 3. Not affected by stray electromagnetic fields and the compensation for temperatures.

STRAIN GAUGES DISADVANTAGES 1. They are relatively complex to fabricate. 2. It has low output, requires signal conditioning circuit.

CAPACITANCE TYPE PRESSURE GAUGE

PIEZO ELECTRIC TRANSDUCER