§7. Using the Data Logger

Data Logger

The data logger’s primary purpose is to help photographers and printers to get a better insight into their light source. When connected to the light integrator, it will record all light and temperature measurements made during exposure and calibration. The data is stored on an SD card as a CSV file, so it can be imported for analysis into a spreadsheet such as Microsoft Excel.

The data logger can also be used to configure certain light integrator settings.

Connecting the Data Logger

The data logger is connected to one of the light integrator’s USB-A connectors using the same type of cable as the sensors.

When the light integrator detects the data logger it shows “DL” and a status indicator dot in the top right-hand corner of the display. If the indicator dot is green, then the data logger is ready for use and has an SD card inserted. If the indicator dot is red, then either the SD card is missing, not inserted properly, or is write-protected.

Recording Data

Once connected, the data are recorded automatically.

Data File Format

The data file is named DDhhmmss.txtwhere:

  • DD is the current date
  • hh is the current hours using a 24-hour clock
  • mm is the current minutes
  • ss is the current seconds

For example, the file 19135922.txtwas created on the 19that 13:59:22.

The contents of a file from a short visible light exposure are shown below:

// EXPOSURE STARTED 21-09-2018 17:54:03
// Light Source: Visible
// Target Dose: 30.0
// Calibration Value: 19.8
0.4,0.4,25.6
0.4,0.9,25.7
0.4,1.4,25.6
0.4,1.9,25.6
0.4,2.4,25.7
0.4,2.8,25.6
0.4,3.3,25.6
0.4,3.8,25.6
0.4,4.3,25.6
0.4,4.8,25.6
0.4,5.2,25.7
0.4,5.7,25.6
0.4,6.2,25.6
0.4,6.7,25.7
0.4,7.2,25.7
0.4,7.7,25.7
0.4,8.1,25.6
0.4,8.6,25.6
// EXPOSURE PAUSED 21-09-2018 17:54:12
// EXPOSURE CANCELLED 21-09-2018 17:54:13

The lines of comma-separated value (CSV) data contain:

  1. The calibrated light reading – for this example the light source was stable, so the reading was 0.4 every time
  2. The cumulative calibrated light reading
  3. The temperature – for this example the temperature is in Celsius, but the system can be configured to use Fahrenheit (see Section ‎7.4:Using the Data Logger for Light Integrator Configuration)

A set of measurements is made about every half second.

Note that there may be small rounding errors in these data. The light integrator itself uses more precise values.

An example file from a calibration exposure is shown below:

// CALIBRATION STARTED 22-09-2018 11:02:16
// Light Source: Visible
// Old Calibration Value: 6.2
0.4,0.0,22.0
0.4,0.0,22.0
0.5,0.0,21.8
0.5,0.0,22.0
… skipped for brevity …
0.5,0.0,22.0
0.5,0.0,22.0
0.5,0.0,22.0
0.5,0.5,21.8
0.5,1.0,22.0
0.5,1.5,21.8
0.5,2.0,21.8
0.5,2.5,22.0
0.5,3.0,21.8
0.5,3.5,22.0
… skipped for brevity …
0.5,56.6,22.0
0.5,57.1,21.8
0.5,57.6,22.0
0.5,58.1,22.0
0.5,58.6,21.8
// CALIBRATION COMPLETED 22-09-2018 11:04:31
// New Calibration Value: 0.9

For calibration, the lines of comma-separated value (CSV) data contain:

  1. The uncalibrated light reading – for this example the light source started with a reading of 0.4 before stabilising at 0.5 for the rest of the exposure
  2. The cumulative uncalibrated light reading – this only starts counting once the light source has stabilised 
  3. The temperature

Calibration measurements are made every five seconds while the light source is stabilising, and about every half second thereafter.

The new calibration value for the current light source is shown at the end of the data file.

Using the Data Logger for Light Integrator Configuration

When the data logger powers-up, it looks for a file called config.txtwhich can contain configuration commands for the system. The available commands, not all of which must be used, are:

  • DATE – sets the system clock date
  • TIME – sets the system clock time
  • TEMPERATURE – sets the units used for temperature display to Celsius (system default) or Fahrenheit
  • CV.UV – sets the calibration value for UV light
  • CV.VISIBLE – sets the calibration value for visible light
  • DELETE – indicates to the data logger whether or not to delete the config.txtfile after use

An example config.txt is shown below:

// Data Logger Configuration File
// Lines starting with two forward slashes are ignored
// Do not add spaces or any other characters to a command

// Dates must be formatted as shown here, i.e. year-month-day
date=2018-09-20

// Times use the 24 hour clock as shown here, i.e. hours:minutes:seconds
time=15:07:00

// Temperature units can be either C for Celsius…
temperature=C
// … or F for Fahrenheit
temperature=F

// Calibration values must be formatted as shown with one decimal place
cv.uv=1.0
cv.visible=1.0

// Instruct the data logger not to delete the config.txt file after use
// If removed then the file will be deleted
Delete=0

// END – the file must end with a blank line or a // line

Unless instructed otherwise with the delete=0 command, then the data logger will delete the configuration file after the commands have been processed. This ensures the system clock is not reset every time the data logger is powered-up. 


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