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modal:modal-analysis:stability-diagram [2026/10/07 21:03] – reid_go-ci.commodal:modal-analysis:stability-diagram [2026/10/09 19:13] (current) – [Calculating the Mode Shapes] reid_go-ci.com
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 ====== EMA Stability Diagram ====== ====== EMA Stability Diagram ======
  
-The **Stability Diagram** tab is the third step of Modal Analysis in EDM, after [[ema:band_selection|Band Selection]]. The Stability Diagram tab features a configurable plot with parameter control over the modal order, estimation method, Mode Indicator Function type, and pole selection.  +The **Stability Diagram** tab is the third step of Modal Analysis in EDM, after [[band-selection|]]. The Stability Diagram tab features a configurable plot with parameter control over the modal order, estimation method, Mode Indicator Function type, and pole selection.  
  
 EDM curve-fits the FRFs in the selected frequency band many times, using a higher model order each time. Poles that stay at the same frequency and damping as the model order increases are real modes of the structure. You pick these poles, and EDM calculates the mode shapes from them.  It also displays Pole information for modal order frequency and damping ratio.  Selected poles are used in mode calculation. EDM curve-fits the FRFs in the selected frequency band many times, using a higher model order each time. Poles that stay at the same frequency and damping as the model order increases are real modes of the structure. You pick these poles, and EDM calculates the mode shapes from them.  It also displays Pole information for modal order frequency and damping ratio.  Selected poles are used in mode calculation.
  
-{{:modal:modal-analysis:stability_diagram.png}}+{{:modal:modal-analysis:polyx_stab_diagram.png?}}
  
 The tab has two main areas: The tab has two main areas:
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   * **SSI**- Stochastic Subspace Identification. Available only for Operational Modal Analysis (OMA) tests, and only if your license includes it.   * **SSI**- Stochastic Subspace Identification. Available only for Operational Modal Analysis (OMA) tests, and only if your license includes it.
  
-**Max modal order**- The highest model order that EDM calculates. The diagram has one row for each model order up to this value. As the hint in the tab says, the modal order is typically four times the number of modes you are curve-fitting. If the value is too high for the data, EDM lowers it automatically and shows a message, for example //"Max Modes will reset to 24."//+**Max modal order**- The modal order is a user defined number which is used to determine the highest order of the polynomial curve of best fit. The diagram has one row for each model order up to this value. As the hint in the tab says, the modal order is typically four times the number of modes you are curve-fitting. If the value is too high for the data, EDM lowers it automatically and shows a message, for example //"Max Modes will reset to 24."//
  
 Click **Calculate stabilization** to calculate the diagram. A progress window opens. You can cancel the calculation from this window. Click **Calculate stabilization** to calculate the diagram. A progress window opens. You can cancel the calculation from this window.
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 Real modes usually show as a vertical column of green **Stable Pole** symbols that continues over many model orders, often at a peak or valley of the MIF curve. Poles that appear at random places, or only at a few model orders, are usually caused by noise or by the math of the curve fit, and should not be selected. Real modes usually show as a vertical column of green **Stable Pole** symbols that continues over many model orders, often at a peak or valley of the MIF curve. Poles that appear at random places, or only at a few model orders, are usually caused by noise or by the math of the curve fit, and should not be selected.
  
-FIXME **Screenshot:** Zoomed-in view of a stability diagram showing a clear column of green Stable Pole symbols at a mode, with scattered red New Pole symbols nearby. +{{:modal:modal-analysis:stability_column.png?}}
-{{:ema:stability_diagram_stable_column.png|}}+
  
 When you move the mouse over a pole, the **Poles and Modes** group shows its information: When you move the mouse over a pole, the **Poles and Modes** group shows its information:
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 Each pole that you select becomes one mode in the results. Each pole that you select becomes one mode in the results.
  
-To select a pole: +To select a pole: simply move your mouse over the stable pole and left click
-  - Move the mouse over a **Stable Pole** symbol in a stable column. Check its information in the **Poles and Modes** group. +
-  - Right-click the pole and click **Add Cursor**. +
- +
-A cursor is added at the pole, and the pole is added to the list of modes, for example //Mode 1: 125.43 Hz, 1.25 %//. The modes are sorted by frequency. +
- +
-FIXME **Screenshot:** The right-click menu open on a pole with Add Cursor highlighted, and the list of selected modes in the Poles and Modes group. +
-{{:ema:stability_diagram_add_cursor.png|}}+
  
 **NOTE:** Some rules apply when you select poles: **NOTE:** Some rules apply when you select poles:
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 **Remove All Cursor**- Right-click the chart and click **Remove All Cursor** to remove all the selected poles. **Remove All Cursor**- Right-click the chart and click **Remove All Cursor** to remove all the selected poles.
  
-===== Right-Click Menu =====+**TIP:** Zoom in on a mode to make it easier to pick the right pole. When you are zoomed in, use the scroll bars or hold the middle mouse button and drag to move around the chart.
  
-Right-click on the chart to open the menu. 
- 
-FIXME **Screenshot:** The right-click menu open on the Stability Diagram chart, showing the Remove Cursor submenu. 
-{{:ema:stability_diagram_context_menu.png|}} 
- 
-**Zoom Back**- Returns to the previous zoom level. 
- 
-**Un-zoom All**- Returns to the full view of the chart. 
- 
-**Add Cursor**- Selects the pole under the mouse. See [[#selecting_poles|Selecting Poles]]. 
- 
-**Remove Cursor**- Removes one selected pole. 
- 
-**Remove All Cursor**- Removes all the selected poles. 
- 
-**X Axis Format**- Shows the frequency axis on a **Linear** or **Log** scale. 
- 
-**Y Axis Format**- Shows the MIF curve on a **Linear** or **Log** scale. This option is available only when a Multivariate, Complex, or Real MIF is shown. 
- 
-**TIP:** Zoom in on a mode to make it easier to pick the right pole. When you are zoomed in, use the scroll bars or hold the middle mouse button and drag to move around the chart. 
  
 ===== Calculating the Mode Shapes ===== ===== Calculating the Mode Shapes =====
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 Then click **Calculate modes**. EDM calculates the mode shapes, saves them to the shape, and opens the **Animation** tab. The message //"The modal shapes are calculated successfully."// is shown. Then click **Calculate modes**. EDM calculates the mode shapes, saves them to the shape, and opens the **Animation** tab. The message //"The modal shapes are calculated successfully."// is shown.
  
-FIXME **Screenshot:** Close-up of the shape-saving options (Save to new shape, Save to existing shape, Shape name, Select shape) and the Calculate modes button. +{{:modal:modal-analysis:poles_and_modes.png}}
-{{:ema:stability_diagram_calculate_modes.png|}}+
  
 **NOTE:** If EDM shows //"Name isn't unique, or FRF is different, or the frequency band overlaps"//, then either the shape name is already used, or the existing shape you chose has different DOFs or an overlapping frequency band. Use a different name, or choose a different shape. **NOTE:** If EDM shows //"Name isn't unique, or FRF is different, or the frequency band overlaps"//, then either the shape name is already used, or the existing shape you chose has different DOFs or an overlapping frequency band. Use a different name, or choose a different shape.