TDMS (Technical Data Management Streaming) is the file format National Instruments software writes measurements in: LabVIEW's TDMS functions, DAQmx data logging, DIAdem, FlexLogger, SignalExpress and VeriStand all save .tdms files. Each file holds groups of channels - long runs of samples such as voltages, temperatures, strain or timestamps - with properties describing them: names, units, the sample rate and start time, the device and the scaling.
Opening one normally needs NI software, the TDM Excel add-in or Python with a TDMS library. This page reads the file itself in your browser: pick a group or channel to see its properties, put up to 8 channels on a chart you can zoom from the whole recording down to single samples, page through the values, and save them as CSV or Excel. Large files are read a piece at a time, not loaded whole, so recordings of many gigabytes open. Nothing is uploaded. It is free to use, with no account and no upload limit, and it runs entirely in your browser: nothing is uploaded, and while the page stays open, a feature you have already used keeps working offline.
The reader was written for this site from National Instruments' published description of the TDMS format (the "TDMS File Format Internal Structure" document): the segments, the incremental metadata that only lists what changed, interleaved and big-endian data, and DAQmx raw data. It was checked against test files made to that description and against the open-source npTDMS library's reading of the same files. If a file of yours does not open, or a value looks wrong next to what LabVIEW or DIAdem shows, please use "Report a problem" below the tool.
- Do I need LabVIEW, DIAdem or the TDM Excel add-in to open a .tdms file here?
- No. The file is read by this page alone, in your browser, on Windows, Mac, Linux, a Chromebook or a phone. NI's free TDM Excel add-in does a similar job inside Excel on Windows; this page needs nothing installed.
- What happens with DAQmx raw data and scaling?
- DAQmx logging stores raw readings from the device with the scaling saved as channel properties. Linear and polynomial scales are applied, so you see the scaled values. Other DAQmx scales (thermocouple, RTD, strain, bridge, table and the like) are not worked out here: those channels show the raw values as stored, and the page says so beside the channel.
- My recording stopped when the program crashed. Will the TDMS file still open?
- Usually, yes. A recording that was not closed properly leaves its last segment unfinished. The page works out how much of it is there, reads every whole value up to the cut, says that the file was cut off, and shows everything before it.
- Why does the Excel file stop at 1,048,575 rows?
- That is the most rows an Excel sheet can hold below its heading row. A longer channel is cut there, with a note saying how many rows were left out. Save as CSV to keep every value: CSV has no row limit, and in Chrome and Edge it is written straight to disk, so files of any size can be saved.
- What is the .tdms_index file?
- It is a copy of the .tdms file's structure without the values, which NI software makes so it can find data faster. It is not needed: open the .tdms file itself. If you only have the .tdms_index, the values are not in it.
- Are my measurements uploaded?
- No. The file is read by your browser on your device, a piece at a time, and nothing from it is sent anywhere.