6.5. SPC Attribute: 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.

When one of the control tests meets your criteria for issuing a warning, it will generate the type of warning you configure.

Overview

1 Alarm ID
2 Setpoint ID (XBar Alarms)
3 Alarm enabled
4 Control Tests
1 Alarm ID

Do one of the following:

  • Select the $SPC_ALARM system Alarm ID.
  • Create your own alarm in the Alarm ID field.

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

Changes the setpoint value to the number of the Attribute test that is in an alarm state.

Upper Specification Limit 0
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 that 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 P, nP, C and/or U 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 .

Control tests (with sample charts) are:

0 Specification limit test
1 One Subgroup beyond upper or lower limits
2 N subgroups in a row on same side of center line
3 N Subgroups in a row all increasing or decreasing
4 N Subgroups in a row alternating up and down
5 N Subgroups our of N Subgroups in a row in Zone A or beyond (same side of center)
6 N Subgroups our of N Subgroups in a row in Zone B or beyond (same side of center)
7 N Subgroups in a row in Zone C, above or below
8  N Subgroups in a row beyond Zone C, above or below center

0 - Specification limit test

Test 0 Failure Calculated acceptable percentage of nonconforming units or defects in the total sample size.

1 - One Subgroup beyond upper or lower limits

Test 1 Failure Any time a subgroup goes beyond the UCL or LCL.

2 - N subgroups in a row on same side of center line

Test 2 Failure When the specified number of subgroups fall on the same side of the center line, one after the other.
Default 7

3 - N Subgroups in a row all increasing or decreasing

Test 3 Failure When the specified number of subgroups increase of decrease in a row on either side of the center line.
Default 7

4 - N Subgroups in a row alternating up and down

Test 4 Failure When the specified number of subgroups increase and then decrease on either side of the center line.
Default 14

5 - N Subgroups our of N Subgroups in a row in Zone A or beyond (same side of center)

Test 5 Failure When N  subgroups in N1 subgroups are in Zone A or beyond on the same side of the center line.
Default 2 out of 3

6 - N Subgroups our of N Subgroups in a row in Zone B or beyond (same side of center)

Test 6 Failure When N  subgroups in N1 subgroups are in Zone B or beyond on the same side of the center line.
Default 4 out of 5

7 - N Subgroups in a row in Zone C, above or below

Test 7 Failure When the specified number of subgroups in a specified number of subgroups are in a row are in Zone C (either or both sides of the center line).
Default 15

8 - N Subgroups in a row beyond Zone C, above or below center

Test 8 Failure When the specified number of subgroups in a specified number of subgroups are in a row are in Zones B, A or beyond (above or below the center line).
Default 8