Function test

Performing a function test allows you to verify that your instrument is functioning correctly. We recommend performing a function test before every deployment. This article explains how to test the instrument sensors, such as the temperature and pressure sensors, and verify that the instrument beams are working as expected.

It is assumed that you have established a stable and reliable connection to the instrument and are familiar with the instrument software. See the Establishing a connection article for instructions on connecting to your instrument.

Configuration

To start the function test, configure the instrument to collect measurements at 1 Hz, then start the measurement and display the data live. For Signature instruments, you must create the configuration manually and upload it to the instrument. For Generation 2 instruments, open the Test instrument tab and select Start function test.

💡NOTE: If the instrument is left collecting data while powered by its internal batteries, it will continue operating until the batteries are depleted. Always stop data collection when testing is complete.

Sensors

Temperature

Verify that the instrument's temperature reading is reasonable. After sufficient time to reach thermal equilibrium, the reading should be close to room temperature.

Pressure

The instrument measures absolute pressure in units of dBar, and below sea level the pressure readings will then include the water and atmospheric pressure. The atmospheric pressure usually fluctuates around 10.13 dBar, and 1 dBar is equivalent to the pressure change over 1 m depth in fresh water (so at 1 m depth the absolute pressure would be 11.13 dBar). During production, the pressure offset is set to 9.5 dBar to output the gauge pressure (pressure relative to the atmospheric pressure). The outcome is that when the instrument is in air, you will see a value of 0.2-0.7 dBar, depending on atmospheric conditions. Be aware, that the pressure sensor cannot output negative values.

Test the pressure sensor by submerging the instrument in water and look at the pressure readings. For example, if the instrument is placed at approximately 0.5 m depth, the pressure reading should increase by the same amount.
An alternative way to test whether the sensor is functioning is by forming a seal around the sensor with your mouth and blowing to observe an increase in pressure. The location of the sensor on a Signature instrument is indicated in Figure 1.

Important: Always adjust the Pressure Offset according to local conditions before final deployment.

Tilt

The tilt sensor is located on the electronic boards inside the housing. Tilt is given in pitch and roll values. Pitch indicates the rotation around the y-axis, while roll indicates the rotation around the x-axis. The x-axis is marked on the instrument head, and the y-axis follows the right hand rule. Ensure that the tilt values correspond with the instrument's orientation by following this procedure: (An example of the expected observations is shown in Figure 3.)

1. Hold the instrument as level as possible while aiming the X direction away from you. The values for "Pitch" and "Roll" should now be close to zero.
2. Tilt the instrument 10º to the right. The "Roll" value should read approximately 10.
3. Tilt the instrument 10º to the left. The "Roll" value should read approximately -10.
4. Tilt the instrument 10º forwards. The "Pitch" value should read approximately -10.
5. Tilt the instrument 10º backwards. The "Pitch" value should read approximately 10.
6. Turn the instrument upside-down while keeping the x-direction directed away from you. Repeat the previous steps and confirm that the values remain consistent.

💡NOTE on AHRS: When using the standard magnetometer, the instrument will adjust automatically for its orientation and pitch and roll will be 0º and the accelerometer Z value should read -1 when pointing downward.  Since the AHRS maintains its orientation, the instrument will observe a roll of 180º and  pitch 0º when pointing directly downwards.

Compass

The compass, together with the tilt sensor, provides instrument heading value. The heading indicates which direction the x-direction is pointing towards.

Start by ensuring that the heading is close to zero when the x-direction is pointing towards North. Since the heading values range from 0 to 360 degrees, pointing the instrument towards North may also result in values close to 360. Check that the compass values correspond to the instrument's orientation while rotating it around its vertical axis. For example, pointing the x-direction towards East should result in a heading value of approximately 90 degrees etc.

Note that magnetic interference from nearby equipment or installations may affect the measurements so take this into consideration when evaluating the result. See the Compass Calibration section for more information.
See also "How To" videos on Nortek Support site.

Beams

Noise floor

The instrument noise floor represent the internal noise of the instrument itself, and is a useful parameter for determining the effective measurement range. For more details about amplitude and its applications, please refer to the Principles of Operation - Currents.

The noise floor can be tested either by having the instrument ping in air or in water. For a precise noise floor measurement, submerge the instrument in water to ensure proper grounding. The noise floor can then be identified by analyzing the amplitude profile at a sufficient distance from the instrument, where the profile flattens out. In air, the instrument will only measure noise, and the amplitude profile should appear as a flat line through the whole profile, representing the noise floor. However, since the instrument is designed to be grounded in water, measurements taken in air may be affected by surrounding noise sources. The first measurement cell is particularly prone to interference from the surroundings, so it is recommended to examine values further along the profile.

Refer to the final test checklist included with the instrument for the expected noise floor value for your specific instrument. Note that these values are obtained by testing in water at the factory and small variations can occur depending on the test environment.

Maximum amplitude  

Test each beam's response by submerging the instrument in water and observe the amplitude in the first measurement cell. You should be seeing a significant increase in amplitude upon submersion. The maximum amplitude observed will depend on the conditions at your test site. You can use the maximum amplitude values found on the final test checklist as a reference for your specific instrument. 

Correlation

While measuring in air, the correlation values will be low. When the instrument is submerged in water you should observe a significant increase. For more information about the correlation parameter, please refer to Principles of Operation - Currents.

Recorder/Memory

1. Test the recorder by starting a Recorder Deployment.
2. Write a name for the file you will record internally and start deployment. A notification may appear warning the instrument is running off an external power supply, press Yes to continue.
3. A pop-up confirming your deployment will appear, press OK. You will be taken back to the Home screen while the instrument is deployed.
4. After a few minutes, stop the data collection by reconnecting to your instrument.
5. Find and retrieve the file you created under Recorder Data Retrieval.
6. Review the collected data in your preferred way, either by converting it in the deployment software or opening it in a post processing software. See that the data is stored as expected.

💡NOTE: 

• If you leave the instrument collecting data using the internal batteries it will run until depletion. Always make sure to stop data collection when testing is complete.
• We recommend starting new deployments with an empty memory. Before you erase the recorder, make sure that you have transferred all the data you want to retain and that the data is in good shape.