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2638A Hydra III Scan Speed

Here are some frequently asked questions regarding scan rate for the 2638A.

Why does scanning one channel slower per channel rate than scanning 20 channels?

At the beginning of each scan the 2638A reads and performs various “housekeeping” tasks and then goes through the scan file.  Once completed, it can scan.  It will add this time into the total scan time whether you are scanning 1 or 22 channels. 

What are some other things that affect my total speed? 

Mixing measurement types makes calculating scan time difficult.  It takes longer to read 10 channels of DC voltage and 5 TC channels and 5 current channels than it would to read 20 channels of just DC Voltage. 

Additional custom settings like channel delay or custom NPLC settings (other than Fast, Medium and Slow) can also add time. 

What is the easiest way to increase scan speed?

Try taking the same kind of reading on each channel.  Eliminate channel delays and custom NPLC settings.  Turn off OTC detection for thermocouples.  Simplify your setup.  



Here is a a graphical example:


Each measurement type has built in settling times which affects over-all scan rate:


  • Settling times are built in to each measurement based on type and range.
  • They cannot be changed by the user and are part of the overall stated scan speeds listed.
  • They do not change with “FAST” “Medium”, “Slow” or “Custom NPLC” reading rates.


How does NPLC relate to the generic scan speed of Fast, Medium and Slow?  Understanding this will help you know when it is appropriate to use a custom NPLC.


For more information on NPLC click on this link: Understanding NPLC

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