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•
Deviation.
A positive number that can be added or subtracted from the setpoint, depending on
the Deviation Type, to determine when an alarm becomes Active or Inactive.
•
Alarm Source.
Depending on the Signal Input Mode and Function selected under the Input+
Display tab, the alarm can be assigned to any of up to three Items, for example to Item 1
(A rate / B rate), Item 2 (A rate), or Item 3 (B rate).
•
Alarm State.
If “Active High” is selected, the Active Alarm State is defined as being above the
setpoint. If “Active Low” is selected, the Acti
ve Alarm State is defined as being below the
setpoint. If “Disabled” is selected, the Alarm State is always inactive.
•
Relay State.
A setting with ties the Relay State to the Alarm State. If “Active On” is selected,
the relay will be closed when the Alarm S
tate is 1. If “Active Off” is selected, the relay will be
open when the Alarm State is 1.
•
Deviation Type.
Three choices are offered: Band Deviation, Split Hysteresis, and Span
Hysteresis. These define how Setpoint and Deviation are to be combined to set Alarm State.
Split Hysteresis for heater control
Band Deviation for component testing
In Band Deviation,
the relay opens (or closes) when the reading falls within the deviation
band, and closes (or opens) when the reading falls outside. Two deviation limits lie symmetric-
ally around the setpoint to create the deviation band. Passbands around a setpoint are often
used for go-no-go component testing.
In Split Hysteresis,
the relay opens (or closes) when the reading goes above the Setpoint plus
one Deviation, and closes (or opens) when the reading falls below the Setpoint less one
Deviation. Two Deviation limits lie symmetrically around the Setpoint to create a deviation
band. A narrow hysteresis band is often used to minimize relay chatter. A wide band can be
used for on-off control.
In Span Hysteresis,
operation is as for Split Hysteresis, except that the Setpoint is always on
the high side, and a single Deviation lies below the Setpoint to create the hysteresis band.
Span Hysteresis is considered by some to be more intuitive than Split Hysteresis.
Summary of Contents for LTE Series
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