PLC Analog ALMA Function

This information applies to the CompactLogix 5370, ControlLogix 5570, Compact GuardLogix 5370, GuardLogix 5570, Compact GuardLogix 5380, CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, and GuardLogix 5580 controllers. Controller differences are noted where applicable.
The ALMA instruction provides level and rate-of-change alarming for any analog signal.

Structured Text
ALMA (ALMA,In,ProgAckAll,ProgDisable,ProgEnable)
Operands

Operand	Type	Format	Description
ALMA	ALARM_ANALOG	Structure	ALMA structure
In	REAL DINT INT SINT	Tag Immediate	The alarm input value, which is compared with alarm limits to detect the alarm condition.
ProgAckAll	BOOL	Tag Immediate	On transition from False to True, acknowledges all alarm conditions that require acknowledgement.
ProgDisable	BOOL	Tag Immediate	When True, disables alarm (does not override Enable Commands).
ProgEnable	BOOL	Tag Immediate	When True, enables alarm (takes precedence over Disable commands).

Function Block

Operand	Type	Format	Description
ALMA tag	ALARM_ANALOG	structure	ALMA structure

Structured Text

Operand	Type	Format	Description
ALMA	ALARM_ANALOG	Structure	ALMA structure
In	REAL DINT INT SINT	Tag Immediate	The alarm input value, which is compared with alarm limits to detect the alarm condition.
ProgAckAll	BOOL	Tag Immediate	On transition from False to True, acknowledges all alarm conditions that require acknowledgement.
ProgDisable	BOOL	Tag Immediate	When True, disables alarm (does not override Enable Commands).
ProgEnable	BOOL	Tag Immediate	When True, enables alarm (takes precedence over Disable commands).

See Structured Text Syntax for more information on the syntax of expressions within the structured text.

Input Parameter	Data Type	Description
EnableIn	BOOL	Ladder Diagram: Corresponds to the rung state. If false, the instruction does not execute and outputs are not updated. Structured Text: If false, the instruction does not execute and outputs are not updated. Default is set. Function Block: If false, the instruction does not execute and outputs are not updated. Default is set.
In	REAL	The alarm input value, which is compared with alarm limits to detect the alarm condition. Default = 0.0. Ladder Diagram: Copied from instruction operand. Structured Text: Copied from instruction operand.
InFault	BOOL	Bad health indicator for the input. The user application may set InFault to indicate the input signal has an error. When set, the instruction sets InFaulted (Status.1). When cleared to false, the instruction clears InFaulted to false (Status.1). In either case, the instruction continues to evaluate In for alarm conditions. Default is false (good health).
HHEnabled	BOOL	High High alarm condition detection. Set to true to enable detection of the High High alarm condition. Clear to false to make detection unavailable for the High High alarm condition. Default is set.
HEnabled	BOOL	High alarm condition detection. Set to true to enable detection of the High alarm condition. Clear to false to make detection unavailable for the High alarm condition. Default is set.
LEnabled	BOOL	Low alarm condition detection. Set to true to enable detection of the Low alarm condition. Clear to false to make detection unavailable for the Low alarm condition. Default is set.
LLEnabled	BOOL	Low Low alarm condition detection. Set to true to enable detection of the Low Low alarm condition. Clear to false to make detection unavailable for the Low Low alarm condition. Default is set.
AckRequired	BOOL	Specifies whether alarm acknowledgment is required. When set to true, acknowledgment is required. When cleared to false, acknowledgment is not required and HHAcked, HAcked, LAcked, LLAcked, ROCPosAcked, and ROCNegAcked are always set to true Default is true.

ALMA Structure Input Parameters

Input Parameter	Data Type	Description
ProgAckAll	BOOL	Set to true by the user program to acknowledge all alarm conditions. Takes effect only if any alarm condition is unacknowledged. Requires a false-to-true transition. Default is false. Ladder Diagram: Copied from the instruction operand. Structured Text: Copied from the instruction operand.
OperAckAll	BOOL	Set to true by the operator interface to acknowledge all alarm conditions. Takes effect only if any alarm condition is unacknowledged. The alarm instruction clears this parameter to false. Default is false.
HHProgAck	BOOL	High High program acknowledge. Set to true by the user program to acknowledge a High High condition. Takes effect only if the alarm condition is unacknowledged. Requires a false -to-true transition. Default is false.
HHOperAck	BOOL	High High operator acknowledge. Set to true by the operator interface to acknowledge a High High condition. Takes effect only if the alarm condition is unacknowledged. The alarm instruction clears this parameter to false. Default is false.
HProgAck	BOOL	High program acknowledge. Set to true by the user program to acknowledge a High condition. Takes effect only if the alarm condition is unacknowledged. Requires a false-to-true transition. Default is false.
HOperAck	BOOL	High operator acknowledge. Set to true by the operator interface to acknowledge a High condition. Takes effect only if the alarm condition is unacknowledged. The alarm instruction clears this parameter to false. Default is false.
LProgAck	BOOL	Low program acknowledge. Set to true by the user program to acknowledge a Low condition. Takes effect only if the alarm condition is unacknowledged. Requires a false-to-true transition. Default is false.
LOperAck	BOOL	Low operator acknowledge. Set to true by the operator interface to acknowledge a Low condition. Takes effect only if the alarm condition is unacknowledged. The alarm instruction clears this parameter to false. Default is false.
LLProgAck	BOOL	Low Low program acknowledge. Set to true by the user program to acknowledge a Low Low condition. Takes effect only if the alarm condition is unacknowledged. Requires a false-to-true transition. Default is false.
LLOperAck	BOOL	Low Low operator acknowledge. Set to true by the operator interface to acknowledge a Low Low condition. Takes effect only if the alarm condition is unacknowledged. The alarm instruction clears this parameter false. Default is false.
ROCPosProgAck	BOOL	Positive rate of change program acknowledge. Set to true by the user program to acknowledge a positive rate-of-change condition. Requires a false-to-true transition while the alarm condition is unacknowledged. Default is false.

Input Parameter	Data Type	Description
ROCPosOperAck	BOOL	Positive rate of change operator acknowledge. Set to true by the operator interface to acknowledge a positive rate-of-change condition. Requires a false-to-true transition while the alarm condition is unacknowledged. The alarm instruction sets this parameter to false. Default is false.
ROCNegProgAck	BOOL	Negative rate of change program acknowledge. Set to true by the user program to acknowledge a negative rate-of-change condition. Requires a false-to-true transition while the alarm condition is unacknowledged. Default is false.
ROCNegOperAck	BOOL	Negative rate of change operator acknowledge. Set to true by the operator interface to acknowledge a negative rate-of-change condition. Requires a false-to-true transition while the alarm condition is unacknowledged. The alarm instruction clears this parameter to false. Default is false.
ProgSuppress	BOOL	Set to true by the user program to suppress the alarm. Default is cleared.
OperSuppress	BOOL	Set to true by the operator interface to suppress the alarm. The alarm instruction clears this parameter to false. Default is false.
ProgUnsuppress	BOOL	Set to true by the user program to unsuppress the alarm. Takes precedence over Suppress commands. Default is false.
OperUnsuppress	BOOL	Set to true by the operator interface to unsuppress the alarm. Takes precedence over Suppress commands. The alarm instruction sets this parameter to false. Default is false.
HHOperShelve	BOOL	High-high operator shelve. Set to true by the operator interface to shelve or reshelve a high-high condition. Requires a false-to-true transition. The alarm instruction clears this parameter to false. Default is false. Unshelve commands take precedence over Shelve commands. Shelving an alarm postpones alarm processing. It is like suppressing an alarm, except that shelving is time limited. If an alarm is acknowledged while it is shelved, it remains acknowledged even if it becomes active again. It becomes unacknowledged when the shelve duration ends.
HOperShelve	BOOL	High operator shelve. Set to true by the operator interface to shelve or reshelve a high condition. Requires a transition from false in one program scan to true in the next program scan. The alarm instruction clears this parameter to false. Default is false. Unshelve commands take precedence over Shelve commands.
LOperShelve	BOOL	Low operator shelve. Set to true by the operator interface to shelve or reshelve a low condition. Requires a transition false in one program scan to true in the next program scan. The alarm instruction clears this parameter to false. Default is false. Unshelve commands take precedence over Shelve commands.
LLOperShelve	BOOL	Low-low operator shelve. Set to true by the operator interface to shelve or reshelve a low-low condition. Requires a transition from false in one program scan to true in the next program scan. The alarm instruction clears this parameter to false. Default is false. Unshelve commands take precedence over Shelve commands.

Input Parameter	Data Type	Description
ROCPosOperShelve	BOOL	Positive rate-of-change operator shelve. Set to true by the operator interface to shelve or reshelve a positive rate-of-change condition. Requires a transition from false in one program scan to true in the next program scan. The alarm instruction clears this parameter to false. Default is false. Unshelve commands take precedence over Shelve commands.
ROCNegOperShelve	BOOL	Negative rate-of-change operator shelve. Set to true by the operator interface to shelve or reshelve a negative rate-of-change condition. Requires a transition from false in one program scan to true in the next program scan. The alarm instruction clears this parameter to false. Default is false. Unshelve commands take precedence over Shelve commands.
ProgUnshelveAll	BOOL	Set to true by the user program to unshelve all conditions on this alarm. If both shelve and unshelve are true, unshelve commands take precedence over shelve commands. Default is false.
HHOperUnshelve	BOOL	High-high operator unshelve. Set to true by the operator interface to unshelve a high-high condition. The alarm instruction clears this parameter to false. If both shelve and unshelve are true, unshelve commands take precedence over shelve commands. Default is false.
HOperUnshelve	BOOL	High operator unshelve. Set to true by the operator interface to unshelve a high condition. The alarm instruction clears this parameter to false. If both shelve and unshelve are true, unshelve commands take precedence over shelve commands. Default is false.
LOperUnshelve	BOOL	Low operator unshelve. Set to true by the operator interface to unshelve a low condition. The alarm instruction clears this parameter to false. If both shelve and unshelve are true, unshelve commands take precedence over shelve commands. Default is false.
LLOperUnshelve	BOOL	Low-low operator unshelve. Set to true by the operator interface to unshelve a low-low condition. The alarm instruction clears this parameter to false. If both shelve and unshelve are true, unshelve commands take precedence over shelve commands. Default is false.
ROCPosOperUnshelve	BOOL	Positive rate-of-change operator unshelve. Set to true by the operator interface to unshelve a positive rate-of-change condition. The alarm instruction clears this parameter to false. If both shelve and unshelve are set, unshelve commands take precedence over shelve commands. Default is false.
ROCNegOperUnshelve	BOOL	Negative rate-of-change operator unshelve. Set to true by the operator interface to unshelve a negative rate-of-change condition. The alarm instruction clears this parameter to false. If both shelve and unshelve are true, unshelve commands take precedence over shelve commands. Default is false.
ProgDisable	BOOL	Copied from the instruction operand.
OperDisable	BOOL	Set to true by the operator interface to disable the alarm. The alarm instruction clears this parameter to false. Default is false.
ProgEnable	BOOL	Copied from the instruction operand.

PLC Alarm Instructions

Analog Alarm Timing Diagrams

PLC Analog Alarm State Diagrams

Input Parameter	Data Type	Description
OperEnable	BOOL	Set to true by the operator interface to enable the alarm. Takes precedence over Disable command. The alarm instruction clears this parameter false. Default is false.
AlarmCountReset	BOOL	Set to true by the operator interface to reset the alarm counts for all conditions. The alarm instruction clears this parameter to false. Default is false.
HHMinDurationEnable	BOOL	High-high minimum duration enable. Set to true to enable minimum duration timer when detecting the high-high condition. Default is true.
HMinDurationEnable	BOOL	High minimum duration enable. Set to true to enable minimum duration timer when detecting the high condition. Default is true.
LMinDurationEnable	BOOL	Low minimum duration enable. Set to true to enable minimum duration timer when detecting the low condition. Default is true.
LLMinDurationEnable	BOOL	Low-low minimum duration enable. Set to true to enable minimum duration timer when detecting the low-low condition. Default is true.
HHLimit	REAL	High High alarm limit. Valid = HLimit < HHLimit < maximum positive float. Default = 0.0.
HHSeverity	DINT	Severity of the High High alarm condition. This does not affect processing of alarms by the controller, but can be used for sorting and filtering functions at the alarm subscriber. Valid = 1…1000 (1000 = most severe; 1 = least severe). Default = 500.
HLimit	REAL	High alarm limit. Valid = LLimit < HLimit < HHLimit. Default = 0.0.
HSeverity	DINT	Severity of the High alarm condition. This does not affect processing of alarms by the controller, but can be used for sorting and filtering functions at the alarm subscriber. Valid = 1…1000 (1000 = most severe; 1 = least severe). Default = 500.
LLimit	REAL	Low alarm limit. Valid = LLLimit < LLimit < HLimit. Default = 0.0.
LSeverity	DINT	Severity of the Low alarm condition. This does not affect processing of alarms by the controller, but can be used for sorting and filtering functions at the alarm subscriber. Valid = 1…1000 (1000 = most severe; 1 = least severe). Default = 500.
LLLimit	REAL	Low Low alarm limit. Valid = maximum negative float < LLLimit < LLimit. Default = 0.0.

Input Parameter	Data Type	Description
LLSeverity	DINT	Severity of the Low Low alarm condition. This does not affect processing of alarms by the controller, but can be used for sorting and filtering functions at the alarm subscriber. Valid = 1…1000 (1000 = most severe; 1 = least severe). Default = 500.
MinDurationPRE	DINT	Minimum duration preset (milliseconds) for an alarm level condition to remain true before the condition is marked as InAlarm and alarm notification is sent to clients. The controller collects alarm data as soon as the alarm condition is detected; so no data is lost while waiting to meet the minimum duration. Does not apply to rate-of-change conditions or to conditions for which minimum duration detection is disabled. MinDurationPRE only applies to the first excursion from normal in either direction. For example, once the High condition times out, the High High condition becomes active immediately, while a Low condition waits for the timeout period. Valid = 0…2147483647. Default = 0.
ShelveDuration	DINT	Time duration (in minutes) for which a shelved alarm will be shelved. Minimum time is one minute. Maximum time is defined by MaxShelveDuration.
MaxShelveDuration	DINT	Maximum time duration (in minutes) for which an alarm can be shelved.
Deadband	REAL	Deadband for detecting that High High, High, Low, and Low Low alarm levels have returned to normal. A non-zero Deadband can reduce alarm condition chattering if the In value is continually changing but remaining near the level condition threshold. The Deadband value does not affect the transition to the InAlarm (active) state. Once a level condition is active, but before the condition returns to the inactive (normal) state, the In value must either: drop below the threshold minus the deadband (for High and High High conditions). OR rise above the threshold plus the deadband (for Low and Low Low conditions). The Deadband is not used to condition the Minimum Duration time measurement. Valid = 0 = Deadband < Span from first enabled Low alarm to the first enabled High alarm. Default = 0.0.
ROCPosLimit	REAL	Limit for an increasing rate-of-change in units per second. Detection is enabled for any value > 0.0 if ROCPeriod is also > 0.0. Valid = 0.0…maximum possible float. Default = 0.0.
ROCPosSeverity	DINT	Severity of the increasing rate-of-change condition. This does not affect processing of alarms by the controller, but can be used for sorting and filtering functions at the alarm subscriber. Valid = 1…1000 (1000 = most severe; 1 = least severe). Default = 500.
ROCNegLimit	REAL	Limit for a decreasing rate-of-change in units per second. Detection is enabled for any value > 0.0 if ROCPeriod is also > 0.0. Valid = 0.0…maximum possible float. Default = 0.0.

Input Parameter

Data Type

Description

ROCNegSeverity

DINT

Severity of the decreasing rate-of-change condition. This does not affect processing of alarms by the controller, but can be used for sorting and filtering functions at the alarm subscriber.

Valid = 1…1000 (1000 = most severe; 1 = least severe). Default = 500.

ROCPeriod

REAL

Time period in seconds for calculation (sampling interval) of the rate of change value. Each time the sampling interval expires, a new sample of In is stored, and ROC is re-calculated. Instead of an enable bit like other conditions in the analog alarm, the rate-of-change detection is enabled by putting any non-zero value in the ROCPeriod.

Valid = 0.0…32767.0

Default = 0.0.

Output Parameters

These output parameters are common to ladder logic.

Output Parameter	Data Type	Description
AnyInAlarmUnack	BOOL	Combined alarm active and acknowledged status. Set to true when any alarm condition is detected and unacknowledged. Cleared to false when all alarm conditions are inactive, acknowledged, or both.
HHInAlarm	BOOL	High High alarm condition status. Set to true when a High High condition is Active. Cleared to false when no High High condition exists.
HInAlarm	BOOL	High alarm condition status. Set to true when a High condition is Active. Cleared to false when no High condition exists.
LInAlarm	BOOL	Low alarm condition status. Set to true when a Low condition is Active. Cleared to false when no Low condition exists.
LLInAlarm	BOOL	Low Low alarm condition status. Set to true when a Low Low condition is Active. Cleared to false when no Low Low condition exists.
ROCPosInAlarm	BOOL	Positive rate-of-change alarm condition status. Set to true when a positive rate-of-change condition exists. Cleared to false when no positive rate-of-change condition exists.
ROCNegInAlarm	BOOL	Negative rate-of-change alarm condition status. Set to true when a negative rate-of-change condition exists. Cleared to False when no negative rate-of-change condition exists.
ROC	REAL	Calculated rate-of-change of the In value. This value is updated when the instruction is scanned following each elapsed ROCPeriod. The ROC value is used to evaluate the ROCPosInAlarm and ROCNegInAlarm conditions. ROC = (current sample of In – previous sample of In) / ROCPeriod
HHAcked	BOOL	High High condition acknowledged status. Set to true when a High High condition is acknowledged. Always set to true when AckRequired is cleared to false. Cleared to false when a High High condition is not acknowledged.
HAcked	BOOL	High condition acknowledged status. Set to true when a High condition is acknowledged. Always set to true when AckRequired is cleared to false. Cleared to false when a High condition is not acknowledged.

Output Parameter	Data Type	Description
LAcked	BOOL	Low condition acknowledged status. Set to true when a Low condition is acknowledged. Always set to true when AckRequired is cleared to false. Cleared to false when a Low condition is not acknowledged.
LLAcked	BOOL	Low Low condition acknowledged status. Set to true when a Low Low condition is acknowledged. Always true when AckRequired is cleared to false. Cleared to false when a Low Low condition is not acknowledged.
ROCPosAcked	BOOL	Positive rate-of-change condition acknowledged status. Set to true when a positive rate-of-change condition is acknowledged. Always true when AckRequired is cleared to false. Cleared to false when a positive rate-of-change condition is not acknowledged.
ROCNegAcked	BOOL	Negative rate-of-change condition acknowledged status. Set to true when a negative rate-of-change condition is acknowledged. Always set to true when AckRequired is cleared to false. Cleared to false when a negative rate-of-change condition is not acknowledged.
HHInAlarmUnack	BOOL	Combined High High condition active and unacknowledged status. Set to true when the High High condition is active (HHInAlarm is true) and unacknowledged. Cleared to false when the High High condition is inactive, acknowledged, or both.
HInAlarmUnack	BOOL	Combined High condition active and unacknowledged status. Set to true when the High condition is active (HInAlarm is true) and unacknowledged. Cleared to false when the High condition is inactive, acknowledged, or both.
LInAlarmUnack	BOOL	Combined Low condition active and unacknowledged status. Set to true when the Low condition is active (LInAlarm is true) and unacknowledged. Cleared to false when the Low condition is inactive, acknowledged, or both.
LLInAlarmUnack	BOOL	Combined Low Low condition active and unacknowledged status. Set to true when the Low Low condition is active (LLInAlarm is true) and unacknowledged. Cleared to false when the Low Low condition is inactive, acknowledged, or both.
ROCPosInAlarmUnack	BOOL	Combined positive rate-of-change condition active and unacknowledged status. Set to true when the positive rate-of-change condition is active (ROCPosInAlarm is true) and unacknowledged. Cleared to false when the positive rate-of-change condition is inactive, acknowledged, or both.
ROCNegInAlarmUnack	BOOL	Combined negative rate-of-change condition active and unacknowledged status. Set to true when the negative rate-of-change condition is active (ROCNegInAlarm is true) and unacknowledged. Cleared to false when the negative rate-of-change condition is inactive, acknowledged, or both.
Suppressed	BOOL	Suppressed status of the alarm. Set to true when the alarm is suppressed. Cleared to false when the alarm is not suppressed.
HHShelved	BOOL	High-high condition shelved status. Set to true when a high-high condition is shelved. Cleared to false when high-high condition is unshelved.
HShelved	BOOL	High condition shelved status. Set to true when a high condition is shelved. Cleared to false when high condition is unshelved.
LShelved	BOOL	Low condition shelved status. Set to true when a low condition is shelved. Cleared to false when low condition is unshelved.
LLShelved	BOOL	Low-low condition shelved status. Set to true when a low-low condition is shelved. Cleared to false when low-low condition is unshelved.
ROCPosShelved	BOOL	Positive rate-of-change condition shelved status. Set to true when a positive rate-of-change condition is shelved. Cleared to false when positive rate-of-change condition is unshelved.
ROCNegShelved	BOOL	Negative rate-of-change condition shelved status. Set to true when a negative rate-of-change condition is shelved. Cleared to false when negative rate-of-change condition is unshelved.

Output Parameter	Data Type	Description
Disabled	BOOL	Disabled status of the alarm. Set to true when the alarm is unavailable (disabled). Cleared to false when the alarm is enabled.
Commissioned	BOOL	The commissioned bit is not used.
MinDurationACC	DINT	Not Used. Value is always 0.
HHInAlarmTime	LINT	Timestamp when the ALMA instruction detected that the In value exceeded the High High condition limit for the most recent transition to the active state.
HHAlarmCount	DINT	The number of times the High High condition has been activated. If the maximum value is reached, the counter leaves the value at the maximum count value.
HInAlarmTime	LINT	Timestamp when the ALMA instruction detected that the In value exceeded the High condition limit for the most recent transition to the active state.
HAlarmCount	DINT	The number of times the High condition has been activated. If the maximum value is reached, the counter leaves the value at the maximum count value.
LInAlarmTime	LINT	Timestamp when the ALMA instruction detected that the In value exceeded the Low condition limit for the most recent transition to the active state.
LAlarmCount	DINT	The number of times the Low condition has been activated. If the maximum value is reached, the counter leaves the value at the maximum count value.
LLInAlarmTime	LINT	Timestamp when the ALMA instruction detected that the In value exceeded the Low Low condition limit for the most recent transition to the active state.
LLAlarmCount	DINT	The number of times the Low Low condition has been activated. If the maximum value is reached, the counter leaves the value at the maximum count value.
ROCPosInAlarmTime	LINT	Timestamp when the ALMA instruction detected that the In value exceeded the positive-rate-of-change condition limit for the most recent transition to the active state.
ROCPosInAlarmCount	DINT	The number of times the positive rate-of-change condition has been activated. If the maximum value is reached, the counter leaves the value at the maximum count value.
ROCNegInAlarmTime	LINT	Timestamp when the ALMA instruction detected that the In value exceeded the negative-rate-of-change condition limit for the most recent transition to the active state.
ROCNegAlarmCount	DINT	The number of times the negative rate-of-change condition has been activated. If the maximum value is reached, the counter leaves the value at the maximum count value.
AckTime	LINT	Timestamp of most recent condition acknowledgment. If the alarm does not require acknowledgment, this timestamp is equal to most recent condition alarm time.
RetToNormalTime	LINT	Timestamp of alarm returning to a normal state.
AlarmCountResetTime	LINT	Timestamp indicating when the alarm count was reset.
ShelveTime	LINT	Timestamp indicates when an alarm condition was shelved the last time. Set by controller when alarm condition is shelved. Alarm conditions can be shelved and unshelved many times. Each time alarm condition is shelved the timestamp is set to current time.
UnshelveTime	LINT	Timestamp indicating when all alarm conditions are going to be unshelved. Value is set only when no alarm condition is shelved yet. The timestamp is determined as sum of the ShelveDuration time period and current time. If an alarm condition is unshelved programmatically or by an operator and no other alarm condition is shelved, then value is set to the current time.

Output Parameter	Data Type	Description
Status	DINT	Combined status indicators: Status Flag CompactLogix 5370, CompactLogix 5380, ControlLogix 5570, CompactLogix 5480, Compact GuardLogix ControlLogix 5580, 5370, GuardLogix 5570 Compact GuardLogix controllers 5380, and GuardLogix 5580 controllers Status.0 = InstructFault X X Status.1 = InFaulted X X Status.2 = SeverityInv X X Status.3 = X X AlarmLimitsInv Status.4 = DeadbandInv X X Status.5 = X X ROCPosLimitInv Status.6 = X X ROCNegLimitInv Status.7 = ROCPeriodInv X X Status.8 = Overflow – X
InstructFault (Status.0)	BOOL	Instruction error conditions exist. This is not a minor or major controller error. Check the remaining status bits to determine what occurred.
InFaulted (Status.1)	BOOL	User program has set InFault to indicate bad quality input data. Alarm continues to evaluate In for alarm conditions.
SeverityInv (Status.2)	BOOL	Alarm severity configuration is invalid. If severity <1, the instruction uses Severity = 1. If severity >1000, the instruction uses Severity = 1000.
AlarmLimitsInv (Status.3)	BOOL	Alarm Limit configuration is invalid (for example, LLimit < LLLimit). If invalid, the instruction clears all level conditions active bits. Until the fault is cleared, no new level conditions can be detected.
DeadbandInv (Status.4)	BOOL	Deadband configuration is invalid. If invalid, the instruction uses Deadband = 0.0. Valid = 0 = Deadband < Span from first enabled low alarm to the first enabled high alarm.
ROCPosLimitInv (Status.5)	BOOL	Positive rate-of-change limit invalid. If invalid, the instruction uses ROCPosLimit = 0.0, which makes positive rate-of-change detection unavailable.
ROCNegLimitInv (Status.6)	BOOL	Negative rate-of-change limit invalid. If invalid, the instruction uses ROCNegLimit = 0.0, which makes negative rate-of-change detection unavailable.
ROCPeriodInv (Status.7)	BOOL	Rate-of-change period invalid. If invalid, the instruction uses ROCPeriod = 0.0, which makes rate-of-change detection unavailable.
Overflow (Status.8)	BOOL	The Overflow bit is set to true when an overflow condition is detected. The overflow bit is cleared to false when the overflow condition has been corrected. Applies to CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, Compact GuardLogix 5380, and GuardLogix 5580 controllers only.