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5.5. SPC Variable: Alarms/Control Tests
SPC can track several different types of occurrences to warn you if a process is slightly off, even if production has not exceeded its control limits on a regular basis. As a result, you can anticipate and handle potential problems before they occur.
Use the Alarm tab in the Variable Quality Characteristics Properties box to specify the:
Type of alarm that will be triggered.
Setpoint ID.
Control test criteria that will initiate alarms or change setpoints.
Note: The SPC variable charts display values between -4 sigma (-4) and +4 sigma (+4). Data outside of this range is not displayed, but it is still used in the chart calculations unless they are excluded .
When one of the control tests meets your criteria for issuing a warning, it will generate the type of warning you configure.
Tip: Use the SPC_ALARM type when creating your own alarm.
The alarm message for SPC alarms consists of the following strings:
Document Name.
Product Name.
Quality/Defect Characteristic Name.
A description of the control check that triggered the alarm.
The value of the sample that triggered the alarm.
An alarm to alert operators.
If alarms are generated for more than one control test, they will stack up and be deleted according to specifications you enter in the CIMPLICITY Alarm Configuration (e.g. the assigned alarm severityfor the assigned alarm).
2
Setpoint ID (XBar Alarms)
Changes the setpoint value to the number of the XBar test that is in an alarm state (1 - 8).
Setpoints provide you with a way to automate corrective action. You can write scripts that trigger the appropriate action whenever the criteria have been met for one of the control tests.
The value of the Setpoint reflects the last test for which an alarm was triggered.
3
Alarm enabled
Enables/disables the alarm.
Check/Clear
The alarm is:
Check
Enabled
Clear
Disabled
4
Control Tests
SPC performs all checked control tests during runtime.
If any control test that is checked fails:
An alarm will be generated (if enabled).
The Nth subgroup and all following subgroups that fail the test criteria display in red.
A tool tip displays the date, time, value and tests that failed when a failed value is right-clicked.
The failure displays on the XBar, Range and/or Sigma chart.
Some tests report when a specified number of values occur in one or more of the following zones.
Zone
Is the area:
A
Up to one standard deviation from the center line.
B
Between one and two standard deviations from the center line.
C
Between two and three standard deviations from the center line.
When you create a control chart, you can select samples for exclusion .