Calibration Of Vacuum Gauge

CALIBRATION OF VACUUM GAUGE AIM: To calibrate a vacuum gauge. APPARATUS: Vacuum gauge, transparent tube (minimum length of 3 meter), Water bath / Water trough. PRINCIPLE: The vacuum gauge measures pressures that are below atmospheric pressure. The calibration is based on the fundamental principle of hydrostatics, which states that pressure at any point in a static liquid is directly proportional to the depth of water column below the free water surface. i.e. P = h ρ g

PROCEDURE: 1. Fill the water trough and mark the level of the free water surface as the datum for measurement.

2. Connect one end of the tube to the gauge and fill the tube with water from the other end until the entire tube is filled with water.

3. Avoid the presence of air gaps or air bubbles in the tube. 4. Without letting the water escape, immerse the free end of the tube in the trough. 5. Lift the gauge 50 cm above the datum and record the reading in mm of Hg. 6. Take subsequent readings for every 50 cm increase in height up to 300 cm. 7. Similarly, take readings while lowering the vacuum gauge.

8. The

above-obtained readings are the indicated pressures. The

theoretical pressures are calculated using P = - h ρ g. (The negative sign is due to vacuum pressure). 9. Calculate the percentage of error using the formula, % Error = (Indicated pressure) – (Actual pressure) x 100 Full Scale Deflection OBSEREVATIONS & RESULTS: Gauge Reading Sr. Height Actual No. (m) pressur e (mm of Hg

Increasing Decreasin Increasing Decreasing Pressure g Pressure Pressure Pressure (mm of (mm of Hg) % % Hg)

SAMPLE CALCULATIONS: To convert from height to mm of Hg, h1 ρ1 = h2 ρ2

h2 =

h1 ρ1 ρ2

Gauge error

GRAPHS: 1.

Gauge pressure against actual pressure

2.

Percentage error against actual pressure CONCLUSION: