ADU

GND

Without GND (ground) the channel data will “float” - and that is difficult to see in the data1.

Warning

The ADU systems need proper grounding

Connect Sensors

  • Connect the electrodes to the ADU
  • Connect the magnetometers magnetometers / fluxgates
  • Connect the GPS antenna
  • Connect the power supply

Booting

  • Connect to a 12 V battery
  • Input range is 10 - 14 V; if the voltage drops below 9.5 V the system powers off23.
  • There are two battery inputs for continuos operation. Replace the battery with lower current first

Booting takes up to 2-3 minutes by default. A shallow calibration and ADC test is carried out4.

GPS

The GPS5 turns green when time and latitude & longitude are fixed. You have to wait for fix - this can also be programmed as a parameter (wait for fix) in the job list6.
Generally the fix is acquired during boot.
The GPS Almanac is invalid after 180 days or after moving the system more than 300 km. In worst case it can take up to 13 minutes until the GPS is updated (your mobile phone can load the Almanac from the Internet, the ADU has to wait for transmission form the satellite).

Selftest

During the selftest the connection to each board and the functionality of each board is tested.
Messages like “channel / board not found” indicate a serious error and the system is dysfunctional.

The scope of selftest is decided by the firmware.
You can force the system to make a full selftest; this avoids a full selftest for 20 days; then switch back to default.

Check Selftest

Go to the WebInterface and check the selftest.
There should no ADB errors.
Acceptable warnings are: * signal too high for gain amplification * contact resistance too high

The first one you get in noisy environments. The second one you get when the electrodes are not properly connected. The second one you may also get when measuring on ice or on very rocky ground. It is your responsibility to check the electrodes and decide to continue or not.

Test Recording

After setting up the system, proceed with some short recordings.

  • 3 minutes @16 kHz
  • 15 minutes @512 Hz

Both together shall give you a good impression about the data quality. Understand that this test measurement is the decision point to continue or not.
Especially when the phase data is good, the site is promising.
A totally scattered plot indicates that you may not be able to process the data even after long recording and using robust processing.

Airborne Recording

The ADU-11e can be set to the following mode:
Start recording when GPS is fixed. This is helpful when you are more busy with your UAV than with the ADU.

Gain Settings

For all ADU systems you can say:
Gain (either “stage 1” OR “stage 2”) shall not exceed 4, especially for the electric field: you may run into trouble with a possible drift.
The ADU-10e/11e run fine without any gain settings. The ADU-08e can be set into “direct mode” and run without gains in the LF mode (aka sample rate ≤ 512 Hz)

Radio Filter

For the ADU-10e the radio filter is fixed.

For LF-Recordings these settings are equal:

RF-4 RF-2 default
ADU-07e ADU-08e ADU-10e

At high resistive ground a possible phase shift is negatable for spectra below 512 Hz.

For HF-Recordings these settings are equal:

For the old ADU-08e you can switch the system into “direct mode”; in this mode the input range for E is ±2.5 V7. This mode is the “ADU-10e” mode.

Footnotes

  1. when hammering steel electrodes into the soil, make sure that they finally good connected after finishing.↩︎

  2. standard car batteries may take 8 hours to drop down from 13 to 12.5 V. And maybe 1 hour from 11.8 to 11.3 V. Keep that in mind!. The switch off level can be set to higher values for Li-Ion batteries.↩︎

  3. the power down voltage can be configured to higher values for Li-Ion batteries.↩︎

  4. ADU-07/08e After long pause or 30 days the system goes into a deep calibration mode and the gains will be measured.↩︎

  5. GPS stands for “Global Positioning System”, but is also used as place holder for GNSS (Global Navigation Satellite System). The ADU uses the GPS system, but is not limited to it. The ADU can also uses Galileo, BeiDou and other systems that are compatible with the GPS protocol.↩︎

  6. in case you make a panic start, and the GPS is not fixed, the system will start anyway. However the system can not sync until the recording is finished - otherwise it would produce a “jump” in the data stream; avoid this!.↩︎

  7. with default mode the input range is ±1.5 V.↩︎