 # Effect of gravity on calibration when Dead weight testers are used

It is very important to establish the gravitational value of the calibration laboratory since it is one of the major quantity during realization of force.

The effect of not doing this could be a variation in force produced by the weight perhaps 0.5% of the force. It is therefore recommended that, the Pressure calibration laboratory establishes local value of gravity (g) and use weights that have been calibrated at that gravitational constant.

For measurement uncertainty of applied force, ‘g’ value shall be known. For realization of applied force more than 0.01%, ‘g’ value shall be calculated using the formula given in below For better than 0.005%, ‘g’ value shall be measured by appropriate authority.

Validation of local ‘g’ and its uncertainty

Formula for calculation of Acceleration due to gravity

An approximate value for g, at given latitude and height above sea level, may be calculated from the formula: Where, A = 0.005 302 4, B = 0.000 005 8, L = latitude, H = height in meter above sea level

To validate this calculated ‘g’ value the simple steps given below can be followed:

Find out the actual ‘g’ value of NMI from the certificate issued by them or by any other source.

Find out the actual ‘g’ value of NMI from the certificate issued by them or by any other source.

From the maps click on the location of NMI, find out latitude and height above sea level. (you can know the ‘g’ value).

Calculate the ‘g’ value using the above formula with these latitude and height. The difference between the calculated value of ‘g’ and the actual value of the NMI should be within 20 to 30 ppm.

Now, go to the maps and click on location of the lab and find out the latitude and height of the place as per the location (you can know the ‘g’ value also).

Calculate the ‘g’ value for this latitude and height. The value obtained should be within 20 to 30 ppm.

Then this value can be taken as ‘g’ value of the lab and uncertainty of ‘g’ can be assumed to be within ± 50 ppm.