2638A Hydra Series III Data Acquisition System/Digital Multimeter
2638A Hydra Series III Data Acquisition System/Digital Multimeter 22638A Hydra Series III Data Acquisition System/Digital Multimeter 32638A Hydra Series III Data Acquisition System/Digital Multimeter 4

2638A Hydra Series III Data Acquisition System/Digital Multimeter

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Price-performance breakthrough in a stand-alone data acquisition system

The Fluke Hydra Series III continues the Hydra Series legacy of precision, multi-channel data acquisition. The new Series III improves on Hydra’s industry-leading thermocouple accuracy and adds a new dimension to how you collect and view data in a portable system.

DC measurement accuracy of 0.0024 %, basic 0.5 °C thermocouple accuracy, full-color display, easy-to-use menu system and industrial safety ratings put the 2638A in a category of its own as a precision data acquisition system. The dedicated 6.5 digit digital multimeter (DMM) mode provides additional utility and value.

The 2638A is expandable from 22 to 66 channels of differential analog inputs. A flexible, 22-channel Universal Input Connector lets you connect and disconnect any type of input to any channel, quickly and easily. Selectable inputs include dc voltage, ac voltage, resistance, thermocouple, RTD, thermistor, frequency and dc and ac current. You can also use the 2638A with optional software and other Fluke data loggers to create a flexible, customized data acquisition system with an almost unlimited number of channels.

2638A Hydra Series III features at a glance

  • DC accuracy of 0.0024 %
  • Thermocouple accuracy of 0.5 °C
  • Up to 66 universal differential isolated inputs
  • On-screen color trend graphing of up to four channels at a time
  • Easy-to-use menu system for setup and data management
  • Input types: ac V, dc V, ac I, dc I, thermocouple, PRT (2, 3, 4 w), thermistor, resistance (2-4 w), frequency
  • Multi-channel real-time data display
  • 6.5-digit bench DMM function for front-panel inputs
  • Monitor function for real-time viewing and charting between scans
  • 20 on-board math channels
  • One-button screen capture of chart or data displays
  • 45 channels/second basic dc scan rate
  • Internal 57,000 scan/setup file memory
  • USB flash drive support
  • Data security features
  • 300 V CAT II input safety rated

Accurate industrial thermocouple measurements

The 2638A incorporates the Fluke patented Universal Input Connector to bring more accuracy to thermocouple measurements than most other instruments in its class. The Universal Input Connector supports 14 common thermocouple types. Temperature-focused menu selections make the 2638A especially suitable for temperature validation applications. If you need to “zero” a large number of thermocouples to a known reference temperature before starting a temperature profiling or validation test, the 2638A will normalize all readings to your reference channel at the push of a button and store the offsets for reference in a supporting data file. If you are conducting chamber tests, heat treating tests under AMS guidelines, or validating temperature devices under 21 CFR regulations, Hydra Series III makes it that much easier to comply.

Universal Input Connector

The Universal Input Connector plugs into any open slot in the 2638A that contains a relay card. The Universal Input Connector has 22 input channels (20 universal inputs and 2 dedicated, low-burden input current channels). Each input connector contains a CJC (cold-junction compensation) device, which is calibrated at the factory. The calibration date and input connector serial number are programed into the input connector and are read by the 2638A when installed. This information is saved in the test setup data file, which is available for review with any associated scan data from a test setup. This feature is a valuable form of traceability if you are working in a regulated industry.

Wiring a test or system setup for 20 to 60 or more channels can be time consuming. With the inexpensive plug-in Universal Input Connector, you can wire your system once, quickly disconnect the connector from your Hydra, then reconnect the Hydra to another input connector for use in a different area.

Other data loggers require you to wire your inputs directly to an expensive “plug-in” active component signal conditioning module. If you need your instrument for a test at another location, you must remove your wiring or use another expensive plug-in signal conditioning module. With Hydra Series III, all your signal conditioning is inside the mainframe, not in your input connector.

Using multiple low-cost Universal Input Connectors gives you the flexibility to leave your input connector at the test site, completely wired, and ready to use. When you need data from that site, simply “plug in” and load your saved setup file. It’s that simple!

Expandable channel capacity

Each 2638A has three slots in the rear panel. Each slot can hold a user-accessible relay card and a 22-channel Universal Input Connector. Three configurations are available, from 22 channels to 66 channels per mainframe. Select a base model with 22 channels and add 22-channel expansion kits when needed. The low cost per channel makes the 2638A a good value for any budget.

Graphical color display with easy-to-use menus

Never get lost again in a complex menu tree while configuring channels or setting up a test. The large, full color, thin film diode (TFD) display enables the Hydra Series III to display comprehensive easy-to-understand data and easy menu navigation.

Back-lighted function keys quickly confirm the active menu selection. The “Record” key illuminates to indicate when the 2638A is recording data in scan, monitor or DMM mode. You always have visible confirmation when your data are being recorded.

Copy-and-paste channel functions make repetitive channel setups a simple task. Top-of-screen menu bar headings always let you know where you are in the setup process. View your data with the push of a button. Page through all channel data and alarms in a quick view mode or scroll through channels and channel statistics individually. Statistics include rate of change, min, max, standard deviation, average, sample size and peak-to-peak information.

Language support

All displayed text in the menus and data display area are translated to eight languages. You can change the language under the instrument setup area with the push of a button. French, Spanish, Japanese, German, Korean, English, Portuguese, Chinese and Russian are all supported languages in the 2638A.

Real-time data charting with historical review

Chart the real-time data of up to four channels at once. Simply select your channels and view real time charting of your measurements. The chart will auto scale for best fit of the displayed values. Zoom in or out to view areas of interest with the push of a button. A history mode enables you to scroll through previously collected data within the scan file…all without a PC and expensive charting programs.

Screen capture function

With one key push on the front panel, you can capture the screen contents of the 2638A directly to the USB drive in .jpg file format. Capture trend chart results or data displays while in any operating mode for reports or just closer review is easy to do.

 Two alarms per channel

Each channel can be set for two alarm points: High-High, High-Low or Low-Low, in any combination. The 2638A compares the set points during each scan. An out-of-range value is reported on the main display and in data files. You can also assign any alarm point to any of six TTL alarm outputs.

 Math channels

Each channel measurement can be set to scale and record your measurement using mx+b gain and offset calculations that are available during your channel setup menu. In addition, each 2638A mainframe has 20 internal math channels with alarm settings for more complex math calculations that record results to your data file during each scan. Each channel result can be used as a variable in another math channel calculation.

 DMM mode adds functionality and value

The Hydra Series III is based on a 6.5 digit (22-bit) precision digital multimeter measurement engine with exceptional measurement quality and resolution – so when you are not using your Hydra to collect multi-channel data, you can use it as a digital multimeter. Front-panel “DMM-style” input jacks and dedicated DMM menu selections enable you to measure dc voltage, dc resistance, ac voltage, ac resistance, Ohms, frequency, and temperature (thermocouples, RTDs and thermistors). Record DMM measurements to a separate DMM data file for later view. The 2638A also displays measurement statistics and graphs measurements right on the main display.

 USB and internal memory

The Hydra Series III features 20 MB on-board memory for storing over 57,000 data records and configuration files. In addition to this large on-board memory, a built-in USB port is available to collect and store large files directly to the USB drive. An on-board file management menu makes moving data files or configuration files from internal or USB memory to your PC easy.

 Memory management

The main panel memory key opens a simple menu for managing data files and setup files. If you want to load a previously saved setup file for a test, simply select your file from either internal memory or from a USB drive and you are ready to start scanning. You can easily move stored internal data to a USB for PC analysis or move setup files to another 2638A. With Hydra Series III you have easy access to data without the need for a direct PC connection.

To help safeguard your test data in the case of a power outage, the 2638A has a menu selection to resume scanning in the same configuration immediately when power is restored. It is just another way the 2638A works with and protects your data.

 Flexible triggers and resolution

To begin a scan, you have several options that can be set in your test setup menu:

  • External trigger to the rear panel
  • Remote SCPI command
  • Alarm trigger
  • Time interval trigger
  • Manual trigger initiated from the front panel

Measurement resolution is at your control with the 2638A. You can choose between standard settings of Fast, Medium or Slow (4.5, 5.5, 6.5 digits) for the resolution you need. You also can select custom measurement speed on individual channels to get the accuracy and resolution to suit your requirements.


A totalizer input located on the rear panel provides a simple counter that records to the data file on every scan. The totalizer count can accumulate up to 1,048,575 counts and be reset from the front panel or remote command.

 Channel statistics

Each channel’s measurement statistics can be viewed at any time. During scanning, monitoring or in DMM mode, you have rate-of-change (per minute and per second), standard deviation, minimum, maximum, and average— all available at the touch of a button.


USB (virtual serial port) and LAN interface connections are available for easy connection to your company network or direct to you PC. Use Fluke DAQ application software for the 2638A or develop your own interface with the standard SCPI command set or use our Lab View driver or Indusoft Web studio to support your specific application needs

 Category II international safety ratings

The Hydra Series III is the only general purpose portable data acquisition system with a Category II safety rating to help protect you and your operators when making real-world measurements in industrial areas. Other data loggers that are not clearly rated for these types of category measurements should be reviewed closely before being used for industrial measurement. Fluke takes your safety and your measurements seriously.

 Data security 

If you use your 2638A in a regulated industry, you will appreciate the data traceability feature option in the instrument setup menu. This two level (administrator/authorized user) system allows an administrator to assign up to five authorized users. The system provides an “audit trail” style record of the operator in any recorded data. Both setup files and resulting data files contain the authorized user ID and timestamp. Guest users may use an existing secured setup file but cannot make changes, and any resulting data file carries the nontraceable label of “Guest.”


The 2638A comes with a factory test report showing all points measured during the manufacturing phase. Accredited calibration certificates are available when specified at the time of order. Calibration of the 2638A is straightforward and requires a password to access the calibration menu from the front panel by your calibration service provider or remotely with Fluke MET/CAL® Calibration Management Software.

 Built-in relay maintenance counter

The key to the isolation and accuracy of the 2638A in part comes from the use of high-quality switching relays inside the unit. Because these relays do deteriorate with extended use, the 2638A has a relay counter for each installed relay board. This will assist a user in anticipating when replacing the  board may be advisable.

Service and CarePlans

The 2638A Hydra Series III ships with a standard one-year warranty. Extended service plans for up to four additional years of coverage (Silver CarePlans) and annual calibration and repair services with expedited handling (Gold CarePlans) are available in most countries.

 Need a large data collection network? No problem!

Need a 200 or 2,000 channel system? Fluke DAQ application software (2680A-APSW) makes it easy to seamlessly collect data from multiple channels and mainframes. Version 6.0 or later of this powerful application software links all Fluke data acquisition products (NetDAQ® Networked Data Acquisition Unit, 2680 Series Data Acquisition Systems and Hydra III) into small or large data collection systems.

If you want to build your own system, use our LabView drivers. Or use Fluke DAQ software with the Indusoft WebStudio HMI software platform to create a customized, graphical process-and-communication-interface with any Fluke data acquisition products.

 Trend Link Software extends system capabilities

Optional Trend Link software (2680A-904) is a comprehensive and powerful trend plotting software package. It allows you to access, view and analyze tremendous amounts of historical and real time data in a trending or chart recorder-like display. With Trend Link software, you can zoom in on points of interest in your data, or zoom out to display a wide overview of longterm trends.