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LJLogM - Windows Only

LJLogM is a simple ready-to-run executable that logs up to 16 input registers from a single device. It displays selected channels on a graph and writes data to file. Generally used for ≤100 scans/second.

Just starting? See our Device Quickstart Tutorials, then our LJLogM Basics Guide.

Supported devices


The application LJLogM is included with the main installation package.

For LabVIEW programmers, the source code is available in the LabVIEW_LJM archive.

Beta Version

There is a beta version of LJLogM available that is much more capable than the release version here.


LJLogM uses command-response mode which is typically used at 100 scans/second or slower.  See Section 3 and Appendix A-1 of the T-Series Datasheet for more information.

If you have recently modified settings and are having problems, close LJLogM, delete LJLogM.cfg in your current working directory, run LJLogM again, select Use default Configuration in the experiment configuration selection window if using LJLogM v1.06+, and you will have the default settings.  If you have problems related to opening the device, select Open First Available Device in the device configuration selection if using LJLogM v1.06+ or delete LJLogM_open.cfg and restart LJLogM if using an older program version.  For problems related to the working directory location, see "Change Working Directory" below.

LJLog vs. LJStream: We suggest that you use LJLogM if possible, and only if you need to go too fast for LJLogM do you then switch to LJStreamM.  LJLogM uses command-response mode, so it acquires and processes 1 scan at a time at the specified interval and is generally used for ≤100 scans/second.  LJStreamM uses stream mode, so each iteration it retrieves and processes 1 seconds worth of scans and is generally used for >100 scans/second.  See Section 3 and Appendix A-1 of the T7 Datasheet for more information.

LJLogM vs. LJLogUD:  LJLogM supports the T-series.  LJLogUD supports the U3, U6, and UE9.

Logging from Multiple Devices: It is possible to log from multiple devices at once by copying and renaming LJLogM.exe then running both the original and copied LJLogM applications. LJLogM.exe can be found by pasting %HOMEDRIVE%\Program Files (x86)\LabJack\Applications in the Windows File Explorer address bar.

Logging for Multiple Experiments (v1.05 and earlier): LJLogM loads configurations from the last working directory. To keep configurations for multiple experiments, you can copy config files (LJLogM_open.cfg and LJLogM.cfg) into the last working directory before opening LJLogM. Alternately, you can create a folder for each experiment and put a renamed copy LJLogM.exe in each of those folders. For example, you could use the following folder structure:


Then LJLogM_force.exe and LJLogM_temp.exe each keep their own working directory, with their own copy of config files and data files.

Logging for Multiple Experiments (v1.06+): LJLogM v1.06 adds new configuration settings. When the program starts, a pop-up window will appear asking for a method to open a device. The Load Open Configs from a File selection is intended only for advanced use with custom open configuration files. See "Device Type & Address (Opening)".

Once the open configuration is selected, another window will appear asking for experiment configuration settings. By default, experiment configurations are saved to LJLogM.cfg.  If default settings are selected and LJLogM.cfg does not exist, default values will be loaded. 

When the program is closed, the selected experiment configuration file is written to the current working directory with the current experiment settings. For example, if  Load Experiment Configuration is selected in the experiment configuration window and a configuration file called MyExperiment.cfg is loaded,  a configuration file called MyExperiment.cfg will be written/overwritten in the current working directory when the program exits.

Experiment configuration files are not intended for direct editing. To make backup or alternate experiment settings see "Save Current Config" below.

Control Descriptions

# Channels: 1-16. Determines the number of rows/channels that will be measured.

Interval (ms): Interval at which this program attempts to scan all channels, update the screen, and write to file.  If those actions take longer than the interval you specify, the program will simply run as fast as it can each iteration.  Use Tables A.1.2 and A.1.4 to estimate how long your samples will take, plus add some ms of overhead for LJLogM itself which will depend on the PC (test with #Channels=1, Interval=0 and FIO0 as the name in the first row).  To determine how fast LJLogM is actually iterating, look at the indicator ms per iteration or the timestamps in the data file.

DevType, ConnType, &  SerialNumber (Opening):  These indicators display information about the device that has been opened.  To control what device is opened, edit the LJLogM_open.cfg file that can be found in the working directory.  Unlike LJLogM.cfg, LJLogM_open.cfg is intended to be directly edited by the user.  If you don't see it, make sure you have opened & closed LJLogM at least once after installation.  This file has an intro line and then three lines to specify Device Type, Connection Type, and Identifier. The default values are ANY-ANY-ANY, meaning that LJLogM will open the first device it can find.  For further information see the Device Opening section of the LJM User's Guide.  Example open configuration file:





If the configuration file is ever rendered unusable, delete it then open and close the application so that it will make a new default configuration file.

This provides a way to run multiple instances at the same time talking to different devices.  Make a copy of LJLogM.exe called LJLogM2.exe, run LJLogM2, set the working directly as desired, and close LJLogM2.  Now edit both LJLogM_open.cfg and LJLogM2_open.cfg to specify the device for each to open.  Requires LJLogM 1.05 or higher.

Name: Specify the desired register Name for each row.  For example, the first row defaults to AIN0, but could be just about any readable register such as AIN9, EIO2, WIFI_STATUS, DIO0_EF_READ_A_F, or AIN3_EF_READ_A.  Any related configuration, such as Range & ResolutionIndex for analog inputs, needs to be done in Kipling before running LJLogM.

Scaling Equations: Should be something like y=a, where y is the scaled output and a is the input voltage of the 1st row.  b through p would be the input voltage of the rest of the rows.  Everything after // is ignored, so use for comments.  A few examples:

y=c // Scaled value equal to raw value from 3rd row
y=100*c // EI-1034/LM34 voltage to deg F
y=c-273.15 // deg K to deg C
y=((c-273.15)*9/5)+32 // deg K to deg F
y=TCVoltsToTemp[K:c:a] // Type K, t/c voltage from 3rd row, CJ temp from 1st row

For more details see the LJLog/Stream Scaling Equations page.

Save Current Config (v1.06+): Click this to save your current experiment configurations. Once clicked, a pop up window will appear asking for a file name and an OK button that will create the file once pressed. The resulting file will be saved to the current working directory with a .cfg file extension.

Write To File:  Click this to start and stop writing to file.  The resulting file is a tab-delimited ASCII file.  Files are written with a .dat extension.  To quickly open in Excel or Open Office Calc, change the extension to .xls or .ods.  To import to a Google Spreadsheet, make the extension .tsv before uploading.

The first column in the file is a timestamp of seconds since midnight January 1st (Universal Time), 1904.  For more information about presenting this timestamp in Microsoft Excel or Open Office Calc see the LJLogUD & LJLogM Timestamps page.

Each row of logged data typically requires ~18 bytes for the timestamp plus ~11 bytes per channel.  So it you log 8 channels once per second for 60 seconds that would be about (18 + 11*8) * 60 = 6360 bytes on the hard drive, and a 1 TB hard drive could hold a few hundreds of years of such data.

Data File Prefix:  LJStreamM uses this as the base string when it makes a file name.  When LJLogM starts a new file, it appends a "_#" to the specified prefix, where "#" is the first unused number from 0-99999.

Max File Size (Bytes):  When the current data file exceeds this limit, the file is closed and a new file is started.

Change Working Directory:  Click this to select the directory where the config file and data files will be saved.  After navigating to the desired directory in the pop-up window, click Select Cur Dir at the bottom-right.  For more details see the LJLog/Stream Working Directory page.

Graph History: Controls how many scans are shown on the graph.  The graph is similar to a strip chart, and simply shows the last n scans.  To clear the graph, change something in the Graph? array of buttons.

# of iterations: Increments by one each time the program loops.

ms per iteration: Displays the actual time in milliseconds of each iteration.  Watch to see if this is greater than the value specified for Interval.


LJLogM does not do configuration.  If you need to do configuration, such as setting the Range of an analog input to a non-default value, you will need to use Kipling.  Close LJLogM, run Kipling, use various tabs to configure everything as desired, and then go to the Power-Up Defaults tab and save the current settings.

Revision History

Beta versions are available on the Beta LJLogM page.

1.06: Added configuration selection and save options.

1.05:  Set minimum value of #Channels to 1.  Fixed problem where name of the exe was not detected properly.  Fixed issue where you could never decrease the number of channels shown on graph.  Changed version check sub-vi so it only shows prompt when new version available, not on version check errors.  Changed scaling sub-VIs to use LJM thermocouple function rather than LJUD function.

1.04:  Skipped version number.

1.03:  Added support for SignedLSWMSW[lsw:msw] function in scaling equations to handle quadrature reads.  For efficiency, scaling equations now skipped if no scaling is needed (e.g. y=a).

1.02:  Changed all text to Segoe UI font so screen items are aligned regardless of system font size.  Changed to show scroll bars.

1.01:  Changed to use this application's filename (w/o extension) to create the names of the config files and registry entry.  Added "Write To File" control to items saved in config file, so the application will now remember how this control was last set.

1.00: First version.

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