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OTT Hydras 3 Basic

Basic communication software

OTT Hydras 3 Basic communication software is a convenient and user-friendly solution for the configuration of OTT dataloggers, for downloading measured values using a notebook, and for automatic remote data collection via modem. Hydras 3 Basic is equipped with a multitude of functions to simplify the setting up of sensors and the maintenance of measurement stations.
  • Hydrometry, Meteorology and Environmental Protection
  • Microsoft Windows 95/98/2000, Windows NT 4.0, Windows XP, Windows Vista, Windows 7
  • Graphical editor, Parametrization and data reading of stations, Autoimport of data, Displaying data
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  • Instrument configuration on-site or via modem
  • Database of measured values and measurement site management
  • Creation and printing of graphs and tables based on measured data
  • Auto and manual import of measured data from measurement sites
  • Manual export of data in various formats
Applicationsoftware OTT Hydras 3 (Basic/Standard/Pro/net)
Hydras 3LT Software

I have Hydras 3 net but am not able to use the commands with the ecoLog 1000?

You need to have a Hydras 3 version 4.0 or higher to have ecoLog 1000 management network support.

Which key assignments are available in Hydras 3?


  • F1: Context-sensitive online help
  • F2: Options dialog (can be activated from main window + graphics window)
  • F3: Language switching (main window)
  • F5: Arrange multiple graphics windows automatically
  • F6: Switch through the open HYDRAS3 windows
  • F11: Rezoom by one step (in main window from map, in graphics window from graph)
  • F12: Rezoom to highest level (otherwise like F11)

Main window

  • Ctrl-Alt-D: Delete selected measurement loop including all sensors (measurement loop must be selected in the tree for this)

Graphics window ("Evaluation" of a sensor):

  • Ctrl-A: Automatic scaling of the value axis (also for multiple graphics)
  • Ctrl-Shift-A: Automatic scaling, but with multiple graphs each graph gets its own axis intercept
  • Ctrl-D: Displays information windows for the tag at the current ruler position.In this window the whole day can be deleted via context menu. Additionally, it is possible to edit the momentary extreme values of the day
  • 2 x Ctrl-D: Now several days can also be deleted!
  • Esc: Closes graphics window
  • +/-: (numeric keypad) Scroll time range right/left
  • Cursor left/right: Move active ruler left/right


  • Double-click on start date in the navigation bar: Display the entire time range available
  • Click with left mouse button in graphic: Place green ruler, with Shift + left mouse button place blue ruler

Communication window

  • Ctrl-Alt-D: Enable debugging (creates H3KTraceX.LOG file in HYDRAS3 path)

What are the system requirements for Hydras 3?

Minimum requirements:

  • Dual core processor with at least 2 GHz
  • 2 GB RAM
  • HDD or SSD with at least 60 GB
  • Operating system: Windows Server 2012 R2 or later, alternatively Windows 7 (32- or 64-bit) or later

Recommended requirements:

  • Dual core processor with at least 3 GHz or quad core processor with at least 2 GHz.
  • 8 GB OF RAM
  • HDD or SSD with at least 80 GB
  • Operating system: Windows Server 2016 or later


For how many users or PCs do I get a license key?

The license key for Hydras 3 is valid for one user at one PC. So if there are several users (the user is identified by the Windows login name) on one PC, several licenses are required. If a key is used by several users or on several PCs, a corresponding notification appears in the Hydras 3 message window (below the menu bar in red letters). OTT also tolerates the use of a license key on several computers of the same user (e.g. a desktop PC and a laptop for field use) as long as they are not used at the same time - this is taken into account in the validation as of version 4.0.4.

If the license of a retired user is to be used for another user or if Hydras 3 is to be installed on a new PC, please proceed as follows:

  1. Confirm or delete message by double-clicking on it
  2. Please make sure that you have the license code for your Hydras 3 version ready. If you cannot find it, please copy the following registry entry to the new computer or to the account of the new user: \HKEY_CURRENT_USER\Software\Ott-Hydrometry\Hydras3\General\GUID (your IT department will certainly help you). Also note the ID in Hydras 3 below the version number in the menu item Help / Info (Tip: because of the short display time please make a screenshot with the button "Print", insert it into the program Paint or similar and save it as file)!
  3. Uninstall Hydras 3 on the old computer (make a data backup of the workspace directories and the program directory of Hydras3 before! Only when moving to a new computer) or delete the above mentioned registry key of the retired user.
  4. Delete the following file from the reported workspace directory: userlist.log
  5. Restart Hydras 3 - the message should no longer appear. If necessary repeat point C) for further workspace directories.


My Hydras 3 crashes reproducible with an "Access Violation". What should I do?

Please contact our HydroService with the following information:

  • Which work steps did you perform before the message appeared?
  • Search the file Hydras3.elf and send it to the HydroService. The file is either in the program directory of Hydras 3 (where the file Hydras3.exe is also located) or under C:\User\<user>\EurekaLog\Hydras3.elf

Can I use a Hydras3net Server V4.x together with Hydras 3 net Clients with V3.x?

In principle, V 3.x clients also work with V 4.x servers. However, we do not recommend this, as some optimizations cannot be used. For example, a V 4.x client only retrieves data from the server that has been added or edited since the last data access.  A V 3.x client, on the other hand, always retrieves all data, which can be very slow for longer time series or shorter intervals.

During the raw data transfer the message "P5" appears. How can I still import the data into the database?

This means that the storage interval of the data collector does not match the periodic setting of the sensor in Hydras 3. The easiest (and fastest) solution is to open the sensor properties in Hydras 3 (right mouse click on the sensor name, then menu item "Properties") and change the data type from "periodic" to "aperiodic". The only difference is that future data gaps within one day (not sent or imported data, but error codes) are no longer marked with the dashed vertical lines.

Hydras 3 often freezes temporarily or can no longer be operated. How can this behavior be improved?

Up to Hydras 3 version 3.x the auto-import runs in the foreground, therefore the user interface freezes during the import (especially of large amounts of data or a large number of files in the auto-import directory). Since version 4.x you can (optionally) run this completely as a background process.


When starting Hydras 3 I get the error message "Network initialization failed. File or directory does not exist: C:\PDOXUSRS.NET Unknown internal operating system error. Directory: C:\". How can I correct the error?

The reason for this error message is the stricter security requirements starting with Windows Vista. By default it is not allowed to create or modify files in the folder C:\". By default the NET DIR setting, which is required to synchronize multi-user access to the Hydras 3 database, is set to C:\. There are the following possibilities to work around this problem under the current Windows operating systems:

  1. One possibility is to set the NET DIR to a directory where you have full permissions. To do this, you need to open the BDE Administrator in the Control Panel and on the Configuration page, click on the node: "Configuration | Drivers | Native | Paradox node and select NET DIR" on the right side. By clicking on the "..." button you can now select a directory. For example, you can select the personal directory for the user, for example C:\Users\ABC, where ABC stands for the user's login name. If Hydras 3 is used in a network with several installations, the workspace is usually located on a file server. Typically, in this case the NET DIR is placed in the workspace directory, since all Hydras 3 users need full write access to this directory anyway.
  2. Create a shortcut to the file Hydras3.exe and add the target as follows "C:\Program Files (x86)\OTT\HYDRAS3\Hydras3.exe" netdir=C:\Users\ABC.
    This procedure is also suitable for starting a laptop with a shortcut in a network environment (with shared NET DIR for all computers) and in the field (local use) with another shortcut. It is nevertheless advisable to additionally set up solution A) for the standard case.

    After adjusting the NET DIR setting, all *.lck files should be deleted manually if necessary. The *.lck files are located in the workspace directory and in the individual station directories below. These files are only created temporarily when a database table is accessed. If there are no such files, this is OK. If all Hydras 3 instances are terminated and such files are there, they should be deleted.

    Additionally you should check at this opportunity whether there are files in the station directories, which start with TDB.... These files are created during import, update of virtual sensors and especially during editing. So if all Hydras 3 instances were finished correctly, they should no longer exist. If there are still instances, they should be deleted, otherwise the import of data into these sensors will be blocked

  3. Run Hydras 3 with administrator rights (right mouse click on Hydras3.exe -> Run as administrator). Windows will then ask if you want to allow this. You must then click on "Allow" accordingly. Probably your IT department will not want to give you the permission permanently. Therefore it is better to use solution 1. or 2.

When calling the menu option Help / Contents ("Online help for Hydras 3") I get the error message: "Feature not included" or "Help is not supported". How can I view the integrated help pages for Hydras 3?

The online help integrated in Hydras 3 up to version V3.x cannot be displayed by default with current Windows operating systems, because Microsoft does not deliver the required program WinHlp32.exe from Windows Vista on. This program must be downloaded from the Microsoft website to use the online help. You can find the appropriate support page (Microsoft) to solve the problem at the following link: Hydras 3 version V4.x now includes an HTML version of the help, which is displayed without further ado. Please note that it is a context sensitive help, which displays the appropriate help page for a mask in Hydras 3 by pressing the F1 key.

Files that are in the AutoImport directory are simply ignored. They are not moved to the Error directory and it seems that they are not processed at all.

Whenever data are written to the database (either by import or editing), a temporary database named TDBxxxx.DB (where xxxx is the sensor number)  is created in the station directory, where the new values are stored first. In a next step, the data are then transferred from the temporary database to the actual database.
If  the temporary database already exists, Hydras3 tries to delete the database. If the database was created by another user or the database is currently open, it cannot be deleted. In this case Hydras3 cannot import in this sensor and ignores the import file. In the AutoImport cycle (every minute), Hydras3 tries again to import the file. Usually as soon as the temporary database is removed, the import will be successful. However there are cases, when the temporary database, which was created by a different user is not properly removed (e.g. because Hydras3 was terminated using the task manager while editing the data), the temporary database remains forever and blocks the AutoImport forever.

Solution: Locate the temporary database TDBxxxx.DB (where xxxx is the sensor number) in the directory of the corresponding station and delete this file and also the TDBxxxx.PX file manually.


How does the communication between Hydras 3 net client and server work?

The communication between a Hydras 3 net client and the Hydras 3 net server is carried out via HTTP and/or HTTPs, depending on the settings, whereby the port number can be set freely (normally 80 or 443). The firewall must allow the connection from the client to the server accordingly.

The individual users use Basic Auth. for the login, whereby the user name must correspond to the Windows user name.