Выражение встречается в следующем контексте:

% Rejection: Relays assigned for % rejection
control are energized when a user programmed
conductivity change (percentage) is measured
between CH1 and CH2. CH1 = high conductivity
(feed), and CH2 = low conductivity (product).
This function is disabled when channel 2 is off.

Заранее спасибо