Channel Config: Mode Alarms

Each channel, except for those that are IRIG, Tacho or Speech, can have mode alarms specified for them.

Mode alarms are defined for each channel in reference to a shaft on the motor, i.e. a tacho channel from the configuration, for the case of rotating machinery.

For each channel, its mode frequency pattern can be defined as a quadratic equation. For each mode, alarms can then be setup.

The alarm conditions are specified giving:

  • The start and end speeds of the tacho over which the alarm is active
  •  A warning level and alarm level
  •  A bandwidth (Hz), centered on the mode frequency.

The safety modes are monitored by the safety service, and the states of mode alarms are reported on the HawkEye FFT based instruments.

Setting up Mode Alarms

  1. Select the “Mode alarms” tab of the Channel configuration screen.
  2. Select a channel. Assign it a reference shaft (tachometer) if present. Alarms cannot be defined for shafts, IRIG, or speech channels.
  3. The Mode grid: Here channel modes are defined as a quadratic function of speed. "y = Ax2 + Bx + C" where y is the central frequency (in Hz) defined as a function of speed, x. The user will specify A, B and C coefficients, including the speed unit. Available speed units are RPM, Hz, or % speed (Hz is recommended). It is also possible to specify the units that the alarm / warning levels will are defined (column “Mode units”). Up to 32 modes may be defined.

    For an Engine Order Tracked alarm, assign "B" to the value of the EO to track. "A" and "C" are 0. Use Hz as the speed unit.

    For a Fixed Frequency alarm, set "C" to the desired frequency. "A" and "B" are 0.
  4. Selected mode (“Mode 2” in our example).
  5. Alarm grid: list of all the alarms defined for the selected mode. User may add a remove alarms, each alarm has a start speed, stop speed, a warning and alarm level (specified in the mode units), and a bandwidth. Up to 32 alarms per mode may be defined.
  6. Graphical representation of the current mode shape and its alarms. This allows the user to define new alarms graphically, rather than editing them in the alarm grid. The user can display:
    1. All modes defined for the channel, or just the selected mode (check box “Display All modes” on the top right corner of the graph)
    2. All the alarms defined for the current mode / all modes, or just the alarm selected in the alarm grid (check box “Display All alarms”).
  7. Click on the arrow to hide the graph, thus making more space for the mode and alarm grids.
  8. Frequency scale
  9. Speed scale, in the speed units defined for the selected mode.
  10. The selected mode, frequency vs speed.
  11. The 2 alarms defined for this mode. The user may click on an alarm contour to change its height (the bandwidth), or its width (the speed range), or click within the alarm and drag it along the mode to change the speed range. Note that the software prevents the user from defining overlapping alarms.
  12. For each channel, it is possible to define a hold on and hold off period, in milliseconds, for both alarm and warning states. When a mode goes out of alarm state, it has to remain out of alarm state for the period specified (alarm hold on) before the HawkEye reports that the mode is out of alarm. When a mode goes in alarm state, it has to remain in alarm state for the period specified (alarm hold off) before the HawkEye reports that the mode is in alarm. Same rule applies for warning hold on/hold off.
  13. Use this button to copy the channel modes and alarms across other channels. Note that the mode grid and alarm grid also have right-click popup menus, allowing the user to copy a mode with or without its alarms, or just a single alarm.
  14. The save / load alarm function are available for both broadband and mode alarms. When saving alarm settings in a CSV file, both types of alarms are saved in the same file.
  15. Option to draw order lines (only for display purposes, those won’t be saved as additional modes).

When a fixed frequency mode is defined (A=B=0), the user may want to define a single alarm that will be active regardless of the speed.

  1. The A and B terms are set to 0; mode has a fixed frequency of 1 kHz
    (C = 1000 Hz).
  2. No shaft is selected; therefore a single alarm will be defined.
  3. The user will define warning and alarm level, as well as the alarm bandwidth (centred on the mode frequency, in our example 1 kHz).
  4. Graphical representation of the warning and alarm level. The bar height represents the alarm level, the bar width the alarm bandwidth. The bar is positioned on the x axis (the frequency) so that it is centred on the mode frequency. Click on the bar and drag it along the frequency axis to change the value of the C term.

For any area which is not covered by any of the alarm modes, in an attempt to cover any unexpected event, the user may define an additional alarm called “Unexpected”.

  1. For the “unexpected” mode, the user has to specify the mode units, in which warning and alarm levels will be defined.
  2. User can right click on the unexpected line, and choose “multi-band unexpected”. If active, the user will be able to define multiple frequency bands, with an unexpected warning and alarm level for each of them. If inactive, a single warning and alarm level will be specified, that applies to the whole bandwidth.
  3. In this example, we are in multi-band unexpected mode. The user has defined 2 frequency bands: 1000 – 2000 Hz, and 2000 – 5000 Hz.

Like the broadband alarms, mode alarms can be modified from the HawkEye, while scanning:

Processing the Alarms

We have mentioned earlier on that the safety service computes mode alarms. This is how the service proceeds, for each channel:

  1. for each mode:
    1. Evaluate the mode equation, using current speed, to find the mode current frequency F. This frequency is reported to the HawkEye.
    2. Finds the alarm bandwidth Bw that applies at current speed (if any), as well as amplitude alarm and warning levels.
    3. Look for the highest amplitude in the FFT, across the bins that are within the region [F-Bw/2,F+Bw/2]. This is the mode amplitude reported on the HawkEye.
    4. Check mode amplitude against alarm and warning level. That will be the mode state reported to the HawkEye.
  2. Check unexpected alarm: amongst all the bins which do not belong to any of the modes already checked in step 1 (in other words, the bins outside any of the [F-Bw/2,F+Bw/2] regions), pick up the bin with highest amplitude. This is the unexpected amplitude and frequency reported. Also, this checks the bin amplitude against the unexpected warning and alarm levels. This is the unexpected state reported. Note that if multi-band unexpected is enabled, the service will do the above in each frequency band 

Displaying the Alarms

  1. This the safety mode bar graph, available in the “Order track” section of the layout editor tool box. For a given channel (in our example, CHANNEL 2) it shows the current amplitude of each mode in a bar chart representation.
  2. Mode 1 is not in alarm, the bar is green.
  3. This is the peak-hold mark, which records the highest amplitude encountered for this mode.
  4. Popup menu option to reset the peak-hold mark, for all modes
  5. Move the mouse over a mode bar, to see the mode current frequency and amplitude.
  6. Displays each mode frequency and amplitude in a table
  7. Table can be shown / hidden via popup menu option
  8. The mode amplitude can be displayed in EU, or as a percentage of the channel maximum EU.
  9. The modes are also displayed on the FFT instrument. Each mode is represented by a line drawn at alarm or warning level (depending on preferences, see 6.14.3) on the amplitude axis. In our example, the modes are below their respective warning level, so the bar is displayed in green. On the frequency axis, the line is centred on the mode current frequency; its width shows the alarm bandwidth.
  10. The square with a cross, displayed in orange, shows that, at this frequency, the signal is above the unexpected warning level.
  11. On CHANNEL 3, the mode called “Mode 1” is in warning, and mode “Mode 2” is in the alarm state. The bar changes to the appropriate colour as it goes above warning (orange) and alarm level (red).
  12. The FFT display also reports the alarm state for mode 1 and mode 2.

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