Data files

When logging data to a computer or USB storage device (with the LI-7550), the LI-7700 outputs data as tab delimited text files, which can be opened in any common spreadsheet application. Each file consists of a file header, diagnostics header, data header, and data. An example data file and descriptions of the file components are shown below.

File header

The header is part of every data file produced by the LI-7700. It includes the following fields:

Table 6‑1. Data file header.
Header Label Description
Model: Analyzer
File Type: Header content descriptor (usually 2)
Instrument: Instrument name
Serial Number: Instrument serial number
Software Version: Instrument firmware version
Timestamp: Date and time the file was created
Timezone: Time zone setting in the instrument

Diagnostics header

If the Diagnostics check box was checked in the PC, USB, or RS-232 outputs, a diagnostic header and column is included in each data file. The Diagnostics Header is a list of potential diagnostics that are output with each file. The DIAG column contains diagnostic values affiliated with each record in the file, and these values encode one or more pieces of diagnostic information. Each value is an integer between 0 and 65535, which can indicate up to 16 diagnostics. The following guide and example can help interpret this diagnostic information.

Table 6‑2. Diagnostic codes output with the LI-7700 data record.
Diagnostics Header Integer Meaning
NOTREADY 32768 Instrument is not ready
NOSIGNAL 16384 No laser signal detected
REFUNLOCKED 8192 Reference methane signal not locked
BADTEMP 4096 Optical path thermocouple failure
LASERTEMPUNREGULATED 2048 Laser cooler unregulated
BLOCKTEMPUNREGULATED 1024 Block temperature unregulated
MOTORSPINNING 512 Lower mirror spin motor on
PUMPON 256 Washer pump motor running
TOPHEATERON 128 Upper mirror heater on
BOTTOMHEATERON 64 Lower mirror heater on
CALIBRATING 32 Calibration in process
MOTORFAILURE 16 Mirror cleaner motor failure
BADAUXTC1 8 Bad thermocouple values
BADAUXTC2 4 Bad thermocouple values
BADAUXTC3 2 Bad thermocouple values
BOXCONNECTED 1 LI-7550 Attached

Interpreting a diagnostic code

If the diagnostic field has a value of 14, this indicates that readings from the thermocouples are bad. This will occur anytime a functioning thermocouple is not attached. The “14” is the sum of values in the “Integer” column from rows 2, 3, and 4 in the table above (2+4+8). If you are using an LI-7550, this value will be “15” under the same configuration.

  1. Identify the integer in the DIAG column of the data file.
  2. Find the largest value in the Integer column of Table 6‑2 which is the value from the DIAG column. The diagnosis associated with that value occurred.
  3. Subtract the DIAG value from the Integer. If the difference is 0, there are no other codes. Otherwise, repeat step 2 using the difference rather than the DIAG code.
  4. Repeat steps 2 and 3 until the difference equals 0.

The following example also shows how to interpret the code. Say, for example, that you encounter the code 17231 associated with a series of logged values in the DIAG column.

  1. Refer to Table 6‑2 and locate the largest value that is 17231.
  2. This is 16384, which indicates that no laser signal was detected. Find the difference: 17231-16384=847.
  3. In Table 6‑2, find the largest value that is the 847.
  4. It is 512, which indicates that the lower mirror was spinning. Find the difference: 847-512=335.
  5. Find the largest value that is 335. It is 256, which indicates that the pump was running.
  6. Find the difference: 335-256=79.
  7. Find the largest value that is 79. It is 64, which indicates that the lower mirror heater was on.
  8. Find the difference: 79-64=15.
  9. Repeating the steps above, it is determined that three thermocouples were not attached or were dysfunctional, and the LI-7700 is connected to an LI-7550.

In summary, if there is a diagnostic value of 17231, the instrument was in the midst of a cleaning cycle while heating the lower mirror.

Note: Any time an odd number occurs in the DIAG field, it indicates that an LI-7550 was in use. Even numbers indicate that there was no LI-7550 attached.

Data header

The data header will include all the variables that are selected in the PC or USB logging window. A UTC time stamp (seconds and nanoseconds) is always output with each record in a file. Therefore, it is not necessary to output date and time unless you wish to have the local time stored with the file. The following list of items may be visible in the data header row, depending on which values are logged:

Table 6‑3. Data header.
Column Heading Description
SECONDS Seconds in UNIX time, or the time the instrument is set to
DIAG Diagnostic value, an integer
CH4 Methane mole fraction (µmol/mol)
CH4D Methane number density (mmol/m3)
TEMP Temperature measured with the LI-7700 thermocouple (°C)
PRESSURE Pressure measured near the optical path (kPa)
RSSI Signal strength (Residual Signal Strength Indicator, 0-100%)
DROPRATE Percentage of 1000Hz scans that were dropped at an output rate of 40 Hz (0-100%).
AUX1 Auxiliary input 1
AUX2 Auxiliary input 2
AUX3 Auxiliary input 3
AUX4 Auxiliary input 4
AUX5 Auxiliary input 5
AUX6 Auxiliary input 6
AUX7 Auxiliary input 7
AUX8 Auxiliary input 8
AUXTC1 Auxiliary thermocouple input 1 (°C)
AUXTC2 Auxiliary thermocouple input 2 (°C)
AUXTC3 Auxiliary thermocouple input 3 (°C)
DATE Instrument date, reflects time zone setting (MM/DD/YYYY)
TIME Instrument time, reflects time zone setting (HH:MM:SS.XXXX)
CHK A check sum feature to check integrity of data


The data is in columns below the DATAH row. The row above the data header includes a list of diagnostic codes that are output with each data file. This information is summarized by the value in the data field called DIAG. These values are described in Diagnostics header.

Status columns

Note: If you choose to log status columns to the data file, status records will be interspersed with the data records by time. Only log status records if you are diagnosing the LI-7700.

When logging to a USB storage device or a host PC, you can choose to log status columns to the log file, to a separate file, or not at all. Status data can also be sent through the RS-232 output. Status data are always logged at 2 Hz. The following header is output with the status file.

Table 6‑4. Status file header.
Column Heading Description
SECONDS Seconds in UNIX time, or the time the instrument is set to
DIAG Diagnostic value, an integer
RSSI Signal strength (Residual Signal Strength Indicator, 0-100%)
REFRSSI Reference Signal Strength (0-100%)
LCTSETPT Laser cooler temperature set point (°C)
LCTACTUAL Laser cooler temperature measured (°C)
BCTSETPT Block cooler temperature set point (°C)
BCTACTUAL Block cooler temperature measured (°C)
CHASSISTEMP Temperature in lower housing (disabled)
OPTICSTEMP Reference junction temperature for top thermocouple (°C)
OPTICSRH Relative humidity in the upper dome (%)
AUXREFTEMP Temperature of Auxiliary Sensor Interface, 7550-101 (°C)
MOTORSETPT Spin motor set point (preferred alignment)
MOTORACTUAL Spin motor position (actual alignment)
USB Device present
USBCAPACITY USB device capacity
USBFREESPACE USB device free space
REF A diagnostic value used in technical support
OPTICSDELTA Temperature difference between air and upper mirror
CHK A checksum feature to check the integrity of data