EFFECT OF MEASUREMENT AND INSTRUMENTATION ERROR ON POTENTIAL READINGS
Among the tools most widely used by a corrosion engineer or technician are a reference electrode and a voltmeter. With them, corrosion potential measurements can be made to assist in determining corrosion of a structure or the effectiveness of a cathodic protection system. However, there are sources of error in these measurements. This paper will discuss some of the more common sources of error and how to reduce them as much as practical.
Common sources of error in potential measurements include measurement circuit IR drop, external IR drop, and problems with the reference electrode. Corrosion control practitioners should understand the possible sources of these errors and use this understanding to reduce them as much as practical.
Standard digital multimeters with a 10 meg-ohm input impedance are not suitable for making error-free measurements in high resistivity electrolytes such as dry soil or concrete. In these applications, one should use either a very high input impedance meter designed for corrosion measurements or a potentiometric voltmeter.