Besides the control output, a controller can have extra relay or logic
outputs that can be configured as high, low, deviation high, deviation
low or deviation band alarms; deviation, that is, from the working
setpoint. The usual convention is to have the relay or logic signal
drop out in the alarm condition. This often is defined as "fail-safe"
because bad relay contacts and broken wires will give a false alarm.
by ArthurHolland | September 1, 1998 | Comments (0)
Peril in the plant can be avoided with effective instrumentation. Transparency is vital at all levels of the operation -- including
cooperation of all of the above-mentioned personnel during
specification, design, documentation, construction and startup.
