The Hydra Data Acquisition Unit (DAU) is a GPIB (IEEE-488) instrument.  That means that it can take data under computer control and can send that data back to the computer.  (Click here for an introduction to IEEE-488 instruments.)  Here, we will examine how to reset the Hydra in a LabView vi.  That LabView vi is ResetHydra.vi.  Then, you can examine taking a single temperature measurement in a LabViewvi, 1TempHydra.vi.

        The steps in taking a single temperature measurement are as follows:

• Reset the Hydra using *RST.  That's done in ResetHydra.vi.
• Issue the command FUNC 1,TEMP,K to set the Hydra to take a TEMPerature measurement on Channel 1 using a Type K thermocouple.
• Issue a command *TRG to trigger the measurement.
• Issue a command LAST? 1 to prepare the last data taken on Channel for transmission from the instrument to the computer.
• Transmit the data to the computer.

        Taking a temperature measurement is more complex than just resetting the instrument.  The steps you need to take are as follows (assuming that the instrument has been reset).  Here's the diagram for the vi.

Here's what you do in this vi.

• Send the following commands using the GPIB Write block in LabView.  In the diagram below, there are three GPIB Write blocks.  Note that each of them uses the same address (3) and the same mode (3) as in the reset vi above.  Here are the commands that are sent to the instrument in each of the GPIB Write blocks.
• FUNC 1,TEMP,K - which sets the function on Channel 1 to be TEMP (TEMPerature measurement) using a type K thermocouple.
• *TRG - which triggers a measurement when the instrument receives this command.
• LAST? 1 - which requests the instrument to prepare the last measurement on Channel 1 for transmission to the computer.
• In LabView you sequence these commands by taking the error signal from each block and feeding it to the next block.  See the diagram reproduced below.
• After setting up the instrument, taking a measurement and preparing the data, you must get the instrument to send the string to the computer.  In LabView you use a GPIB Read block.  It's found in the same general place as the GPIB Write block.

        The vi above will take a single temperature measurement once the instrument has been reset.  That allows you to put the temperature mesurement inside a loop and put the reset outside the loop.  If you use this in an application where speed is critical, you might also want to consider putting the GPIB Write block that sets the channel and the measurement type outside the loop, separating it from the rest of the operations above.