Write Timetable Data to TDMS File

This example shows how to write timetable data in various time channel layouts from MATLAB® to a TDMS file.

For this example, you have measurents of revolution and electrical current of a circular saw in a scenario where it stops on detecting contact with skin.

Load the data to workspace.

load("sawstopper.mat")
whos

  Name                       Size             Bytes  Class        Attributes

  circular_saw_data      23572x2             378432  timetable              

fileNameTCNone = "sawstopper_none.tdms";
fileNameTCSingle = "sawstopper_single.tdms";
channelGroup = "Circular Saw Data";

Write Timetable Without a Time Channel

On specifying TimeChannel as "none", the start time and time step are added as properties of the channel. This time channel layout can be used only with a timetable that is regular in time, that is, with uniform time steps.

tdmswrite(fileNameTCNone, circular_saw_data, ChannelGroupName=channelGroup, TimeChannel="none");
info = tdmsinfo(fileNameTCNone);
info.ChannelList

ans=2×8 table
    ChannelGroupNumber     ChannelGroupName      ChannelGroupDescription         ChannelName         ChannelDescription    Unit    DataType    NumSamples
    __________________    ___________________    _______________________    _____________________    __________________    ____    ________    __________

            1             "Circular Saw Data"              ""               "Revolutions (1/min)"            ""             ""     "Double"      47144   
            1             "Circular Saw Data"              ""               "Current (A)"                    ""             ""     "Double"      47144   

The channel names in the TDMS file map to the original timetable variable names.

Use the tdmsreadprop function to inspect the start time (wf_start_time) and time step (wf_increment) of the data.

channel = info.ChannelList.ChannelName{1};
prop = tdmsreadprop(fileNameTCNone, ChannelGroupName=channelGroup, ChannelName=channel)

prop=1×7 table
            name             description    unit_string            wf_start_time            wf_start_offset    wf_increment    wf_samples
    _____________________    ___________    ___________    _____________________________    _______________    ____________    __________

    "Revolutions (1/min)"        ""             ""         2022-04-19 14:18:32.304446999           0             2.8e-06         23572   

Read the data from the TDMS file and visually analyze the data using a stacked plot.

stackedplot(tdmsread(fileNameTCNone, TimeStep=seconds(prop.wf_increment)));

Write Timetable with a Time Channel

By default, the time channel layout is TimeChannel="single", which means a time channel is created that contains a timestamp for every sample. Typically this time channel layout is useful when writing measurements that are irregular in time.

tdmswrite(fileNameTCSingle, circular_saw_data, ChannelGroupName=channelGroup, TimeChannel="single");

Inspect the contents of the file. See that a time channel called "Time" is created, which is derived from the time column of the original timetable.

info = tdmsinfo(fileNameTCSingle);
info.ChannelList

ans=3×8 table
    ChannelGroupNumber     ChannelGroupName      ChannelGroupDescription         ChannelName         ChannelDescription    Unit     DataType      NumSamples
    __________________    ___________________    _______________________    _____________________    __________________    ____    ___________    __________

            1             "Circular Saw Data"              ""               "Time"                           ""             ""     "Timestamp"      47144   
            1             "Circular Saw Data"              ""               "Revolutions (1/min)"            ""             ""     "Double"         47144   
            1             "Circular Saw Data"              ""               "Current (A)"                    ""             ""     "Double"         47144   

Read the data from the TDMS file, and visually analyze the data using a stacked plot with the time channel as the x-axis.

stackedplot(tdmsread(fileNameTCSingle, ChannelGroupName=channelGroup, RowTimes="Time"));