Standard measurement techniques for cathodic protection on storage tanks & pipelines in oil & gas, power, water/wastewater, and other infrastructure industries.
Potential measurement

Measurement circuit error:
Measurement of structure to electrolyte potential is done through high resistance voltmeter to reduce measurement error. The measurement error is caused in the metering circuit by voltage drop in the earth due to meter current Im.
The equation is Vm/Etrue
= Rm/Rt where
Vm = Measured potential across voltmeter in V
Etrue = Ep = True potential in V
Rm = Resistance of meter in ohm
Rt = Rm+Rpe+Rre+Rc = Total circuit resistance in ohm
where Rpe and Rre are structure to earth and reference cell to earth resistance and Rc is cable resistance
As Rm is increased, the ratio of Rm/Rt approaches to 1 and measurement error is reduced.
If total circuit resistance is not known and true potential is required then the equation is Etrue= Vh (1-k)/ 1-k*Vh/Vl where
Vh and Vl are measured voltage with highest and lowest input meter resistance and k= Rl/Rh, Rl and Rh are lowest and highest input resistance


Author's Bio: 

Marcep Inc. is a division of Marcep Group which has a JV with some of the major projects over the world and has entered the Asian market in sharing knowledge to the industry.