A method and apparatus for automatically testing the integrity of an
inductive loop in a vehicle detector system. A check loop is placed
adjacent each inductive loop in a multi-channel vehicle detector system.
Each check loop is periodically activated by the vehicle detector to
simulate a vehicle load on the associated inductive loop. Samples
representing loop inductance at different activation periods are compared
with a standard. When the result exceeds the standard, the inductive loop
is subjected to additional sample testing with decreasing time intervals
between sampling. After a number of additional samples exceed the
standard, the inductive loop is deemed failed.