Standard Watch conditions

The system strategy includes Watch instructions for each monitor defined in the system. These instructions are used to survey method runs, and instruct the system to call a specified block or an instruction when a particular monitor signal meets a given condition. As long as the condition is not met, the block is not activated.

Note: Watch instructions are shown in the Instruction box of the Text Instructions editor, indicated in the Block pane by a green line that shows the start and duration of the watch.

The breakpoint when the Watch instruction is issued determines when the watch begins, not when the block is activated.

A watch is active from the point at which it is issued until

• the Watch condition is met

  or

• a new watch is set for the same monitor

  or

• a Watch_Off instruction is issued for the monitor.

Watch instructions are inserted in the Instruction box of the Text Instructions Editor. The table below describes how to do this.

The table below describes the Watch options that are available on the Test drop-down list of the Parameters field:

Note: For slope values, use the Differentiate function in the Evaluation module to measure the slope of the test chromatogram. The Simulate Peak Fractionation technique can also be used to find the slope values.

Two Watch conditions are available for systems with air sensors, although they may be handled differently depending on the system. The table below describes the conditions and their explanations:

Note: To use the Watch_AirSensor instruction for air sensors, the Alarm_AirSensor setting must be disabled.

The table below describes possible actions when a watch condition is met:

Permanent settings

Permanent settings for Delta_Peak and Delta_Base are entered with the WatchPar instruction (for example WatchPar_UV, WatchPar_Cond) under System:Settings in the System Control module (see the Administration and Technical Manual).

Temporary settings

Temporary settings that apply only for the duration of a given run can be entered in the Instructions field of the Instruction box in the Text Instructions editor. Select Alarms&Mon and then WatchPar.

The Delta_Peak setting helps the software to detect valleys, peaks and peak maximum, and to ignore noise in the chromatogram.

The Delta_Peak value should be set

• large enough so that signal noise does not activate the conditions

  and

• small enough so that the condition is activated close to the valley or peak.

As a general guideline, set the value to 2-3 times the noise level and 5-10% of the smallest expected peak height. If you set a too high value you can prevent a new peak from being detected after a local minimum.

The Delta_Peak setting

• sets the threshold for signal increase after a local minimum that will be interpreted as a valley for the Less_Than_Or_Valley condition. A valley and a new peak are detected when the signal increases to 102% of the local minimum plus the Delta_Peak value.

  Note: A valley is detected only after a Peak_Max has been detected.

  Example:

  If there is a local minimum at 0.05 AU and a Delta_Peak of 0.01 AU, a valley will be detected at:

  (1.02 x 0.05)+0.01=0.111 AU

• sets the threshold for signal decrease after a local maximum that will activate the Peak_Max condition. Peak_Max is detected when the signal falls to the specified fraction of the most recent peak maximum minus the Delta_Peak value.

  The figure below illustrates the Delta_Peak setting where Peak_Max is detected when the signal falls by Delta_Peak from a local maximum if the Peak_Max factor is set to 1:

The Delta_Base setting helps the software to determine when the baseline is considered to be stable. In other words, it defines the permitted variation for the Stable_Baseline condition. For this condition to be activated, the signal may not vary by more than the Delta_Base value up or down over the time interval specified in the Stable_Baseline condition in the Watch instruction.

Note: The Delta_Base setting affects the Stable_Baseline condition only.

The condition Watch Stable_Baseline is met if the signal does not deviate by more than ±Delta_Base from the baseline during the time interval specified for the watch. The baseline value is determined by the signal at the start of the watch. If the condition is not met, a new interval is started with a new baseline value defined by the signal level at the start of the new interval.

The illustration below shows an example of this: