Field shorthand for a potential that falls short of criterion, meaning less negative than required: a pipe at -780 mV instant-off against a -850 target is reading low. Because the numbers are negative, newcomers sometimes say high when they mean more negative, while veterans just say low or under-protected. Low readings get chased down to shorted casings, broken bonds, dead rectifiers, spent anodes or fresh coating damage.
Three posts east of the river are reading low, check the rectifier and the casing at the highway.
Also heard as
- under criterion
- under-protected
Related terms
-850 mV criterion
Steel counts as protected when its potential is -850 mV or more negative against a copper sulfate electrode.
Pipe-to-soil potential
Voltage between a buried pipe and a reference electrode on the soil surface, the basic CP measurement.
Shorted casing
Road or rail crossing casing pipe that has made metal contact with the carrier pipe and steals CP current.
Rectifier
Transformer-rectifier unit that turns AC power into adjustable DC current for an impressed current CP system.