Overview
DTect-IT is capable of running a limit analysis on a monitored signal. A limit analysis tests various measured values against user programmed limits. When a limit condition is exceeded, an alarm is triggered. This will alert an operator when an abnormal running condition occurs in the process and will assist in preventing disruptions in the operation.
Limit Analysis Wizard
The Limit Analysis wizard eases the setup of a Limit Analysis by guiding the user through the settings step by step. To set up a new Limit Analysis, click the Create button in the General Settings menu and select Limit. This launches the Limit Analysis Wizard. Perform the following steps in the wizard to create the analysis:
- Press Begin.
- Select or Create a new sensor for the analysis to utilize.
- Select a Channel and Unit Type from the drop down menu.
- Select a filtering mode.
- Enter a name for the analysis and Press Finish.
After finishing the analysis, the Limit analysis settings menu will be opened.
Limit Analysis User Interface
The Limit Analysis user interface displays one live graph for monitoring data in real time. When running a limit analysis, DTect-IT tests the measured data against user programmed limits. If a limit is exceeded, an alarm is triggered. The following buttons and features are available in the limit analysis user interface:
Performing a Limit Analysis
To perform a limit analysis, start by setting limits. This can be done three ways:
- Using the slider bars in the user interface
- Setting a numerical value in the settings menu for the analysis
- Running the machining process in Learn mode.
If not utilizing Learn mode, run the machining process without starting the analysis. While the process is running, observe how the signal data is affected by the limits. Make small adjustments to the limits, as needed. Once limits are set, start the analysis with by pressing the Start button. When the analysis starts, DTectIT monitors the measured data against the set limits until the Stop button is pressed or a stop command is received from the CNC. After the limit analysis starts, the limit slider bars will be replaced by three limit status dials. The three limits are upper (red), warning (yellow), and lower (blue). The status dials fill as the monitored data approaches the limits. Additional data is displayed in the bottom right hand side of the graph. This data includes the upper and lower peaks, the current actual data measurement and the run count, if enabled. When a limit is met or exceeded (falls below for lower limit), an alarm occurs. The alarm condition can vary based on the limit settings for the analysis. This includes, but is not limited to, limit type and limit sensitivity. Various limit types have different alarm conditions and behavior. Limit sensitivity acts as an alarm delay for all limits.
Using Learn Once to Set Limits
Limit analysis allows limits to be programmed automatically with the Learn Once feature. To utilize Learn Once, it must first be enabled in the analysis settings menu. Once learn is enabled, pressing the Learn Once button prompts DTect-IT to enter Learn mode the next time the limit analysis is started. When the analysis is started, the background color of the live graph changes to green and DTect-IT begins monitoring the signal data for the upper and lower peaks of the signal. While DTect-IT is in Learn mode, run the complete machining process to be monitored. When the process is complete, press the Stop button to end the analysis. DTect-IT utilizes the recorded upper and lower peaks of the signal to adjust the limits and graph scale on the User interface. Limits are calculated using the peaks (upper and lower) of the data signal and an Autoscale percentage set by the user in the analysis settings. The default Autoscale percentages are 30%, 20%, 30% for the Upper limit, Warning Limit, and Lower Limit respectively. The following is an example of limit calculations for a process with an upper peak of 20HP and a lower peak of 10HP, assuming default Autoscale percent:
- Upper Limit = Upper Peak + (abs(Upper Peak - Lower Peak)*0.30) = 23HP
- Warning Limit = Upper Peak + (abs(Upper Peak - Lower Peak)*0.20)= 22HP
- Lower Limit = Lower Peak - (abs(Upper Peak - Lower Peak)*0.30) = 7HP
Utilizing Limit Sensitivity
Limit Sensitivity is an optional feature available in DTect-IT that alters how alarms are triggered during a Limit Analysis. When Limit Sensitivity is enabled in the analysis setting, an additional slider bar becomes available on the user interface. ( Limit Sensitivity allows DTect-IT to delay an alarm from triggering even after the alarm condition is satisfied. The delay is applied to all enabled limits in the analysis. Adjusting the Limit Sensitivity slider bar changes how long an alarm is delayed after the alarm condition is satisfied. Increasing the Sensitivity applies a short alarm delay whereas decreasing Sensitivity applies a longer delay. This is represented visually in the Limit Sensitivity dial. When an alarm condition is satisfied, the corresponding Limit Sensitivity dial begins to fill. The Limit Sensitivity bar fills quickly for increased sensitivity and it fills slowly for decreased sensitivity. When the bar is completely filled, the alarm triggers.
Limit Types for Limit Analysis
Limit types change how the limit analysis triggers an alarm condition based on the signal value. The following Limit types are available:
- Running: An alarm occurs when the sensor signal value:
- exceeds the warning limit value
- exceeds the upper limit value, or
- falls below the lower limit value
The Limit analysis remains in alarm until the alarm condition is no longer satisfied (e.g. the sensor signal value falls below the set warning limit value). Running limit type is available for upper, warning and lower limits.
- Latching: An alarm condition is triggered in the same manner as a running limit type, but the limit analysis remains in alarm until the analysis is reset. Latching limit type is available for upper, warning and lower limits.
- Must Exceed: The must exceed limit type is only available for the lower limit. When the must exceed limit type is selected, the signal value must exceed the lower limit at least once during the limit analysis. When the limit analysis is stopped, the analysis will trigger a lower alarm if the signal value did not exceed the lower limit.
- Work Latching: This limit utilizes accumulated work to calculate the warning limit. A warning alarm is triggered when the accumulated work exceeds the value of this limit. l Work Must Exceed: This limit utilizes accumulated work to calculate the lower limit. The accumulated work must meet the value in this limit before the analysis is stopped, otherwise a lower alarm is triggered.
Example: Latching Alarms vs Running Alarms
When an alarm is triggered for a running limit, DTect-IT leaves the alarm state if the alarm condition does not continue to be satisfied. This can be seen in Figures 2-8 and 2-9.
When an alarm is triggered while utilizing latching limits for a limit analysis, DTect-IT remains in the triggered alarm condition until reset. The Reset button appears in the user interface after a latching alarm is triggered. An example of a latched alarm can be seen in Figures 2-10 and 2-11.
Using Work for Limits
Work limits can be set for warning and lower limits in a Limit Analysis. When a work limit is enabled in the limit settings, DTect-IT tests the accumulated work measured from the sensor (also referred to as "area under the curve") against a learned work value. The limits must be set by utilizing the Learn Once feature (See "Using Learn Once to Set Limits". To utilize a work limit, set the limit type in the limit settings. The following options are available:
- Warning Limit-Work Latching: An alarm is triggered when the accumulated work exceeds the work value set for this limit. The resulting alarm must be reset to be cleared.
- Lower Limit- Must Exceed Work: An alarm is triggered if the accumulated work does not exceed the work value set for this limit.
After adjusting the settings for work limits, set the learn once feature and run the limit analysis. As the analysis runs, DTect-IT calculates and learns the accumulated work. When the process is complete, the work limit values are set utilizing the following formulas:
Warning Limit = Learned Accumulated Work+ (Learned Accumulated Work * Learn Auto-scale %) Lower Limit = Learned Accumulated Work * Learn Auto-scale %
On the next run of the limit analysis, DTect-IT will test the accumulated work against the learned work limits. As work accumulates, the limit status dials fill as normal, but are a representation of accumulated work.
Status Icons
In the analysis tab for a limit analysis, icons will appear based on the alarm status of the analysis. If any alarm condition is triggered when the analysis is running, an icon will appear in the analysis tab. Refer to Table 2-3 for descriptions of possible status icons.