SPC Alarms

CitectSCADAautomatically monitors several special kinds of conditions that are specific to SPC data. When specific patterns or events occur to an SPC tag, it will set the appropriate alarm. Typically these alarms are related to, and used in conjunction with, the XRS control charts.

SPC alarms are configured differently to standard digital alarms

to provide for this extra functionality. SPC alarms needs to be configured using the Advanced Alarms form. You use the SPCAlarms Cicode function to check for the condition of the alarms:

Note: An SPC alarm can only be defined on an Alarm Server in the same cluster as the Trends Server that contains the SPC tag (though the variable tag referenced in the SPC tag can be on a different IOServer cluster).

The SPC (Trends) Server checks for any specified alarm conditions. When one is detected, it informs the Alarm Server that an alarm has occurred. Be aware of the number of subgroups displayed on your SPC charts, and the number used in SPC alarm calculations (as set by the [SPC]AlarmBufferSize parameter). If these two values differ, SPC alarms might not correlate with your SPC charts.

Name	Description
XFreak	Single point greatly differs (2 sigma) from the center line.
XOutsideCL	Process mean outside either of the control limits (UCL or LCL).
XAboveUCL	Process mean above the upper control limit (UCL).
XBelowLCL	Process mean below the lower control limit (LCL).
XOutsideWL	Process mean outside the alert limits which are 67% of the UCL and LCL.
XGradualUp	Process mean is gradually drifting up to a new level indicated by several consecutive points above the mean.
XGradualDown	Process mean is gradually drifting down to a new level indicated by several consecutive points below the mean.
XUpTrend	Several points continuously increasing in value.
XDownTrend	Several points continuously decreasing in value.
XErratic	Large fluctuations that are greater than the control limits.
XStratification	Artificial constancy. Several consecutive points are close to (within 1 sigma of) the center line.
XMixture	Several consecutive points are far from (outside 1 sigma of) the center line.
ROutsideCL	Process range outside either of the control limits (UCL or LCL).
RAboveUCL	Process range above the upper control limit (UCL).
RBelowLCL	Process range below the lower control limit (LCL).

Name

Description

XFreak

Single point greatly differs (2 sigma) from the center line.

XOutsideCL

Process mean outside either of the control limits (UCL or LCL).

XAboveUCL

Process mean above the upper control limit (UCL).

XBelowLCL

Process mean below the lower control limit (LCL).

XOutsideWL

Process mean outside the alert limits which are 67% of the UCL and LCL.

XGradualUp

Process mean is gradually drifting up to a new level indicated by several consecutive points above the mean.

XGradualDown

Process mean is gradually drifting down to a new level indicated by several consecutive points below the mean.

XUpTrend

Several points continuously increasing in value.

XDownTrend

Several points continuously decreasing in value.

XErratic

Large fluctuations that are greater than the control limits.

XStratification

Artificial constancy. Several consecutive points are close to (within 1 sigma of) the center line.

XMixture

Several consecutive points are far from (outside 1 sigma of) the center line.

ROutsideCL

Process range outside either of the control limits (UCL or LCL).

RAboveUCL

Process range above the upper control limit (UCL).

RBelowLCL

Process range below the lower control limit (LCL).

Note: The above alarms rely on n number of consecutive points to generate the alarm. The value of n can be set for each type of alarm through SPC parameters.

Advanced Alarms
Alarm Tag	Feed_Above_UCL
Alarm Desc	Un-controlled variation
Expression	SPCAlarms("Feed_SPC", XAboveUCL)
Comment	Several samples are above UCL