Record 16 Days of Data From a Single Sensor and Single Session

 

 

 

As an example, if you wish to quantify a low frequency and low intensity activity over prolonged periods of time (low back movement, gait activities…), you can easily program the sensor to record at 20Hz or 50Hz and even profile the duration of data recorded each day, say 8am to 6pm each day, placing the sensor into deep sleep mode for the remaining hours in that day. The following day, based on the profile set, the sensor will automatically wake up at the desired time and start recording data on the profile you previously set for the session.

Conversely, if you wish to quantify high frequency and highly intense activity over shorter periods of time (baseball throw, landing from a hop…), you can modify the sensor profile to record data at 1,000Hz, ramp up the accelerometer scale to ±100G and program the sensor to wake up on specific activity (shake sensor).

Some of the variables are briefly described below:

Frequency of Data Capture

It is important to understand the desired frequency of data capture for the activity you are wanting to measure. Based on the Nyquist criterion, the sampling frequency required will be at least twice the highest frequency contained in the signal or activity that you are aiming to record, or information about the signal will be lost. If you have questions on this topic, please reach out to the dorsaVi team as we have worked with >200 research groups globally and are well versed at working through your data capture requirements. 

Accelerometer Range

Accelerometers measure acceleration forces that may be static, like the force of gravity, or dynamic being caused by moving or vibrating the sensor. By measuring the amount of static acceleration due to gravity, you can quantify the angle the device is tilted at with respect to the earth and through sensing the amount of dynamic acceleration, you can analyze the way the device is moving.

Many accelerometers will have a range of between ±2g up to ±16g and their measurement output will be specified in ±g. This is the greatest amount of acceleration the sensor is able to measure and accurately represent as an output. For simple gait metrics, an accelerometer measuring ±4g may be adequate, whereas for running and sprinting activities we have found that accelerometers need to be able to measure ±16g, and in some elite runners you may need to go to ±24g, to avoid clipping of data. For other applications, in which acceleration or deceleration occurs at a rapid rate, (eg: concussion episodes) the range of the accelerometer will be required to be far higher where the sensor will need to measure ±100, ±200g or even up to ±400g to capture such rapid events. dorsaVi sensors are able to cover each one of these applications described above.

Gyroscope Range

The gyroscope measures rotational and/or angular velocity with the units of angular velocity measured in degrees per second (°/s) or revolutions per second (RPS). The range of the gyroscope is usually expressed by the maximum value of the input angular rate in the forward and reverse directions, for example: ±300 °/s. The higher the value, the more sensitive the gyroscope will be to measuring the angular rate. 

Again, it is critical to work through the exact metrics that you are most interested in. Do you want to measure the spin of a record player, or the angular rotation of a pitchers arm ? The majority of wearable sensors have gyroscopes with a range of 250°/s, whereas higher grade gyroscopes are able to measure angular rates at 2000°/s and even 4,000°/s. Let us know if you want to learn more about capturing rotational movements at high speeds? 

Sleep Mode

The accelerometer has a clever sleep mode function that allows the sensor to operate in various levels of activity such as deep sleep, light sleep and fully awake mode. The different levels of activity will alter the battery life in different ways. If we place a sensor in full active mode with all chips turned on at maximum frequency and ranges of recording, the battery life may be 24-48 hours. If we profile the sensors to record at ranges and frequencies required for capturing specific metrics and utilize the sleep modes for low or no activity periods, we are able to record data for up to 16 days, to allow a deeper understanding of how a subject moves across multiple days/weeks. 

Flash Memory

A flash memory chip allows data to be stored on the sensor itself, meaning the sensor is able to be worn for remote sessions, away from all other devices and independent of Wifi and Bluetooth (BT) comms and still record all activity undertaken by the subject. The data is able to be offloaded from the sensor via BT or other means. 

If would like to learn more about any of these themes or parameters, please reach out to us at dorsaVi and we can connect you with the most appropriate member of our technical team. 

References:

  1. https://www.analog.com/media/en/training-seminars/tutorials/MT-002.pdf 
  2. https://www.dimensionengineering.com/info/accelerometers
  3. https://learn.sparkfun.com/tutorials/gyroscope/all

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