Monitoring application

This section details ways to automate measurement acquisition in order to set up the OhmPi as a monitoring tool.

Repeated acquisition at fixed intervals

The easiest way to set up time-lapse acquisition is to perform repeated acquisition of a sequence at fixed intervals. Repeated acquisition can be initiated from the three different Interfaces.

Example of code for monitoring.

### Run multiple sequences at given time interval
k.settings['nb_meas'] = 3  # run sequence three times
k.settings['sequence_delay'] = 100 # every 100 s
k.run_multiple_sequences()  # asynchronous
# k.interrupt()  # kill the asynchronous sequence

Scheduled acquisition using crontab

One can automate acquisitions by calling in a script via crontab (a LINUX built-in scheduler) at scheduled timings. One way of achieving this is to rely on a python script detailing the desired operations (i.e. run_sequence, etc.), which is called in a bash script. The bash script is needed here to activate the python environment (ohmpy) and can potentially feature additional basic operations, such as selecting appropriate settings, or sending data to a remote server.

Example of a python code (run_sequence.py) taking a sequence filename and a settings filename as arguments

args = sys.argv
if len(args) > 1 :
    sequence_filename = args[1]
    settings_filename = args[2]
else:
    print("args missing")


### Define object from class OhmPi
k = OhmPi()

### Set or load sequence
k.load_sequence(sequence_filename)    # load sequence from a local file

### Run contact resistance check
# k.rs_check()

k.update_settings(settings_filename)

### Updating export_path to match sequence filename
k.settings['export_path'] = os.path.join('data',os.path.split(sequence_filename.replace('.txt','.csv'))[1])

### Run sequence
k.run_sequence() #save_strategy_fw=True) #plot_realtime_fulldata=True)

In this example, the prefix of the data filename (export_path) will match the prefix of the sequence filename. This python script (called run_sequence.py) can be run in the terminal as follows:

python -m run_sequence.py my_sequence.csv my settings.json

Then a bash script is required to load in the python environment and calling the python script, such as:

Example of a bash script (run_sequence.sh) calling in run_sequence.py

#!bin/bash
USER="pi"  # change if other username
PROJECT="OhmPi"

SURVEY=$(ls /home/$USER/$PROJECT/sequences/$1*)
echo $SURVEY

#Load settings
cd /home/$USER/$PROJECT
SETTINGS=$(ls settings/$2.json)

#Load ohmpy environment
source /home/$USER/$PROJECT/ohmpy/bin/activate

#run python script
python /home/$USER/$PROJECT/run_seq.py $SURVEY $SETTINGS

#Add automatic processing scripts or transfer to backup serve, e.g.
/usr/bin/rsync -avz -h /home/$USER/$PROJECT/data/$1* login@your_server.org:/path/to/copy/on/your/server

This script can then be added to a crontab scheduler by calling in

crontab -e

And updating the schedule according to your needs:

Example of crontab entry

# m h  dom mon dow   command
0 12 * * * /usr/bin/bash /home/pi/OhmPi/run_sequence.sh my_sequence my_settings >> cronlog.log

IoT acquisition and sensor trigger

Example node-red experiment