ShapeArrays typically measure the static tilt relative to gravity in order to determine their shape in the ground. By taking multiple shape readings, it is possible to determine deformation. In some cases, ShapeArrays can be used to measure dynamic acceleration or vibration. It is important to note that a ShapeArray can be used to measure either static tilt or dynamic acceleration. It cannot measure both at the same time. It is also important to note that the accelerometers used in ShapeArrays have a 3 dB bandwidth of 50 Hz. This means that for frequencies above 50 Hz the signal will be diminished, and acceleration measurements will be attenuated.
NOTE: It is not possible to measure static tilt and dynamic acceleration at the same time.
To record dynamic acceleration data from a ShapeArray, SAARecorder must be configured to achieve the highest possible communications rate with the ShapeArray. If it is turned on, AIA mode should be turned OFF for the ShapeArray (see Figure 1 below). Also, the baud rate should be set to the highest possible value (230400 bps) using the ‘Communications | Baud rate’ menu item (Figure 2 below).
Figure 1: Make sure that the AIA option is unchecked when making measurements of dynamic acceleration or vibration.
Figure 2: Make sure that the baud rate is set to the highest possible value (230400 bps) for measuring dynamic acceleration or vibration.
For model 3 and higher ShapeArrays, in non-AIA mode and using a baud rate of 230400 bps, it is possible to achieve a data sampling rate of about 200 Hz when sampling a single ShapeArray segment. If more segments are being sampled at the same time, the drop off in the data rate is approximately linear in relation to the number of segments being sampled. For example, if two segments were being sampled at the same time, the expected data rate would be 100 Hz, and if four segments were sampled, the expected rate would be 50 Hz.
Because most ShapeArrays have many segments, the vibration software available in SAARecorder allows you to choose which segments are actively sampled for dynamic acceleration. To do this, click on the ‘Data and graphs | Get vibration data’ menu item of SAARecorder. For details on the vibration measuring software of SAARecorder, please see: 'Get Vibration Data' guide.
As previously stated, when sampling data in vibration mode, it is not possible to also measure the static shape of the ShapeArray at the same time. To measure the static shape of the ShapeArray, it is necessary to close any graphs of vibration data (if opened) and use AIA mode (check the ‘Use Averaging-in-Array (AIA) mode’ checkbox) in the ‘Basic Settings’ window of SAARecorder.
Measurements of dynamic acceleration and vibration are only available on a PC platform, running SAARecorder. The logger-based systems currently used with ShapeArray are not fast enough to collect dynamic acceleration data.