ADEV Tool is a web-application for computing sigma-tau plots, such as Allan deviation (ADEV) and Hadamard deviation (HDEV). It works from user’s specified data files, including multichannel data. The result is plotted and tabulated. To support timing applications, the calculator will accept frequency or phase data. It also directly supports several common scaling methods.
How to use the calculator
The first step to using the ADEV calculator is to select a data file. The calculator can accept most common ASCII-text files, see Data File Format section for additional information. Begin by pressing the File button to open a file selection dialog box. Locate the file you would like to process and press the Open button. Next, define the data parameters to apply. Here is a brief description or each parameter:
- Deviation – Select the type of computation desired: Allan deviation (ADEV), Hadamard deviation (HDEV) or modified-Allan deviation (MDEV). ADEV and HDEV can be normal or overlapping.
- Data type – Define if the data files contains samples of phase or frequency.
- Scaling – After defining the data type, specify how the data is scaled.
- Freq Nom (Hz) – Some data scaling methods require the nominal frequency of the clock as part of the scaling necessary to plot in “parts-per”. If necessary, enter the nominal frequency in Hz. For Fractional Frequency or Phase in seconds, this parameter can be ignored.
- Tau spacing – Specify the interval between plot points. The “Full-Decade” option will generate the most complete plot, but requires additional time to compute.
- Tau (sec) – Define the sample period of the data in seconds.
- Reference – Optional, can add a reference trace to your plot, see section Reference Trace.
After selecting the desired parameter settings, press Submit. A popup will show a snippet of the file and some file-related options. Select the options desired and press Apply to plot the result.
- Do you support large files? Yes. File size is essentially unlimited, but the deviation type on large files is limited to ADEV.
- Do you support multiple traces? Yes, but all channels must be columns in one file and have identical type and scaling. We also limit the number of channels to 5.
- Do I need java to use the ADEV calculator? No!
- Can the ADEV calculator ignore outliers? Not at this time.
Data File Format
The ADEV calculator accepts ASCII-text files such as CSV files. In general, additional whitespaces are ignore. The ADEV calculator supports up to 5 channels of data in a single file. A data column is assumed to be from a given channel. Columns can be separated by common delimiters such as white spaces, commas and semicolons. It ignores extra spaces and tabs. It does require that each line end with a terminator, which can be either a carriage return, a linefeed or both.
You can selectively ignore up to 4 lines at the beginning of the file to accommodate a header. The file load engine tries to guess the number of header lines, but this estimate can be changed in the file upload popup.
The calculator does not support timestamped data. But if the first column of the data files contains timestamps, there is an option to ignore this column. To use this option, be sure this data is sampled at regular intervals.
Large Data files (> 50 Mbytes)
For most data files, the ADEV tool will load the entire file into memory before it computes the deviation. This is efficient and allows rapid changes to parameters without reloading the file. To support large data files, the calculator automatically moves into a special mode that computes the data as a stream. This avoids allocating large blocks of RAM, but it has limitations. The primary limitation is that the deviation-type is limited to Allan deviation. After computing the ADEV, rescaling or changing Tau can be done without reloading the file and is therefore quite fast. But changing parameters such as tau spacing and data type require reloading the data. Be sure these are correct before pressing Apply. The large file mode is automatically entered if the data file defined by the user exceeds approximately 50 MBytes.
|Tau (sec)||Cs Beam Clock||H2 Active Maser||Rb Gas cell||Precision Crystal|
For timing applications, it is often useful to compare performance to existing clock technologies. This is an option to add a canned trace which approximates the performance of some common clock technologies. By selecting one of these options, a reference trace is added to your plot. Deselect to remove it. The adjoining table lists to available reference traces.
Note–These numbers do NOT represent any particular clock or product. They are just ballpark numbers provided for reference only.
In general, units of Allan deviation are the same as the input data. However, in precision timing applications, the ADEV is generally presented in units of fractional frequency (parts per). By plotting different devices using these units, stability and drift can be compared directly. Consequently, the ADEV calculator is designed to always plot the results in fractional frequency units. However, it does require the user to accurate specify the units of the data. We provide some parameters options for several common scaling methods.
TAU (Sample Period)
For this tool, Tau is the sample period in seconds. The data is assume to have a uniform sampling period and have no missing data. The sample period must be provided to correctly compute the Allan deviation.