www.miinet.com
Moore Industries-International, Inc.
- 10 -
User’s Manual
224-790-00K
May 2018
Alarm Terminology
Before setting up the SPA
2
, or incorporating the unit in your application, Moore Industries suggests
that all users take a few moments to become familiar with some of the terms associated with the use
of process instrumentation alarms and relays.
Failsafe Alarms -
are de-energized when tripped, energized when the process input is at a
non-alarm level. Non-failsafe Alarms are energized whenever tripped, de-energized when the
process input is at a non-alarm level. The relays in the SPA
2
can be switched from failsafe to
non-failsafe at any time by the user.
Normal -
is the term used to describe the “shelf-state” of relay contacts. The contacts of a Normally
Open relay are open (infinite resistance) when the relay is not energized. The contacts of a Normally
Closed relay are open when the relay is energized (closed when not energized).
Note:
Sometimes a non-alarm input level is referred to as being in a “normal” condition. This
practice is intentionally avoided in this manual. Do not confuse the term “normal”, as in Normally
Open or Normally Closed, with a non-alarm input condition. In this manual, “normal” is an exclusive
reference to the shelf state or quiescent state of an alarm’s relay contacts, whether open or closed.
Latching and Non-latching Alarms -
once tripped, a latching alarm remains in alarm until the input
returns to a non-alarm level AND is manually reset (using the MR terminals). Non-latching alarms
return to a non-alarm state whenever the process input returns to the Reset Point. The SPA
2
relays
can be set by the user to function as either latching or non-latching.
Delay
- A delay can be set to avoid false trips. The unit must be in an alarm condition for the delay
time before a relay trips.
The following terms relate to
Trip Alarms
:
The
Trip Point
is the process input level at which the user wants an alarm relay to change state,
typically going into an alarm condition, or “tripping.” In the SPA
2
, the user sets the trip point for each
installed relay.
High/Low Alarms -
High Alarms trip when the process input goes above the trip point. Low Alarms
trip when the process input drops below the trip point. Each of the SPA
2
outputs can be set by the
user to function independently as either high or low alarms.
The
Reset Point
is the process input level at which the user wants an alarm relay to change state,
typically going from alarm to non-alarm. The reset point is not necessarily the same as the trip point,
because most applications call for a buffer zone or
“Deadband”
around the trip point to allow for
minute fluctuations in the process input. In the SPA
2
, the reset point is determined by the deadband
setting. Latching SPA
2
alarms will not “clear” unless the reset point has been reached or passed
AND the manual reset contacts have been shorted. The
Deadband
is the range in which an alarm
remains tripped even after the process input has returned to or passed the trip point. Deadband is
not required. When it is not incorporated into an alarm application, the trip point and reset point are
the same.
Programmable Limit Alarm Trips
SPA
2
SECTION 1
