Let me explain the generic concept of SCPI's READ/MEASure/FETCh commands. Sorry but I am not familiar with the Agilent model you are using, but the concept is common for most of SCPI-based instruments that implement these command family.
Basically MEASure? and READ? do initiate a new measurement, which may require long time to complete measurement depending on instrument type. On the other hand, FETCh? just queries measurement data *WITHOUT* initiating new measurement. The measurement data that the FETCh? query returns is the cached data that was acquired at previous MEASure/READ or INITiate. (INITiate command initiates a new measurement but does not query the data.) Therefore using FETCh? query without initating will cause a SCPI error.
For example,
READ? (or MEASure?)
initiates a new measurement then returns data
This is basically equivalent to
INITiate
FETC?
If the INITiate command initiates a measurement then generates multiple measurement data set such as VOLTage, CURRent, POWer, FREQuency, etc at once, you can send INITiate only once then query multiple data by multiple FETCh? queries like:
INITiate
FETCh:VOLTage?
FETCh:CURRent?
FETCh: POWer?
FETCh:FREQuency?
This only takes the time for once-time measurement as the new measurement is taken only once by INITiate. If you used READ or MEASure instead of FETCh, it would take 4-time longer to acquire all the 4 items, plus could not operate simultaneous measurement for multiple items.
Mind that INITiate command may require a sub node such as INITiate:SEQuence2 depending on the instrument, therefore you should reference to the operation manual for more about detail syntax for INITiate/FETCh/READ/MEASure.
Makoto
このメッセージは 05-11-2006 12:48 PMに Makoto が編集しています。
