AnsweredAssumed Answered

vrf what is the meaning of externally-triggered measurement??

Question asked by VRFuser on Oct 30, 2006
A lot of people, including myself have written volumes over the years on triggering.  In the simplest of terms, a trigger is a point, usually a point in time when an action occurs.  The action is most often the start of a measurement or measurement sequence, but it can also define something like a switch opening/closing or the start of the output of a signal.
 
In common instrumentation, there are a number of ways defined to initiate a trigger.  This is generally controlled by the command TRIGger:SOURce in a SCPI based instrument.  Trigger sources are generally immediate, internal, external and BUS.  Immediate means that there is effectively no triggering and just do it now.  Internal says to trigger from some point on the signal being acquired.  This point is defined by a trigger level and slope.  For example, trigger on the rising edge of a waveform when the signal level exceeds 3.3 Volts.  These triggers do not require any special actions in a measurement program as they are internal to the measurement itself.
 
The other two require some external action in order to complete the sequence.  In BUS triggering, the trigger signal is sent over the communications bus.  For GPIB, this is through the GET universal command (group execute trigger).  When this command is received, pending operations are triggered. In EXTERNAL triggering, the trigger signal is supplied electrically through an auxiliary connector.
 
In the later two cases, the trigger signal needs to be inserted into the measurement sequence, either by sending the trigger command (BUS) or by initiating some external action that fires off the sequence (i.e. initiating a pulse generator that will provide the signal).  This can be handled in one of two ways in VEE.  The simplest is to divide the measurement into two equal pieces.  For a SCPI instrument, rather than use MEASure, which does it all in one chunk, you would use CONFigure, then INITiate.  You would then insert the trigger, and finally perform a FETCh operation to retrieve the data.
 
The other way is to do the measure, but just before you do so, you fire off a new thread that performs the actions and generates the external trigger signal.
 
This is a very short and very simplified explanation of triggering.  I hope it isn't too cryptic.  There are pages and pages of additional topics, such as logic triggering, delayed triggering, time vs. event, etc, etc.
 

Jay Nemeth-Johannes 
Smart Sensor Systems 
720 SW 14th Street
Loveland, Colorado 80537
(970) 663-0006  (Office)
(970) 290-9797 (Cell)
HYPERLINK "http://www.smartsensorsystems.com/"www.SmartSensorSystems.com

 


  _____  

From: Jess You* [mailto:youjess@gmail.com]
Sent: Sunday, October 29, 2006 9:03 PM
To: VRF
Subject: [vrf] what is the meaning of externally-triggered measurement??


Hi all...wish to have some clarification on the statement below

externally-triggered measurement
 
If i am giving command to some instruments using Agilent VEE, what does the statement above refer to? A bit confuse when reading the e-book provided....
Please help me.....i am an idiot in engineering...
Regards,
Jess
--- You are currently subscribed to vrf as: jay.johannes@completetest.com To subscribe please send an email to: "vrf-request@lists.it.agilent.com" with the word subscribe in the message body. To unsubscribe send a blank email to "leave-vrf@it.lists.it.agilent.com". To send messages to this mailing list, email "vrf@agilent.com". If you need help with the mailing list send a message to "owner-vrf@it.lists.it.agilent.com". Search the "unofficial vrf archive" at "www.oswegosw.com/vrf_archive/".


---

To subscribe please send an email to: "vrf-request@lists.it.agilent.com" with the word subscribe in the message body.
To unsubscribe send a blank email to "leave-vrf@it.lists.it.agilent.com".
To send messages to this mailing list, email "vrf@agilent.com".
If you need help with the mailing list send a message to
"owner-vrf@it.lists.it.agilent.com".
Search the "unofficial vrf archive" at "www.oswegosw.com/vrf_archive/".  

Outcomes