Reference Multimeter and 8 ½ Digit Multimeter
Triggering Measurements
111
An example of using Delay would be if you are making a sensitive high-value
Ohms measurement. You would want to start the measurement manually and
have sufficient time to exit from the surrounding area. Assume the Trigger
subsystem is in the default state to start with so that the Trigger Event is set to
Immediate. Set Delay to a suitable value, for example 20 seconds. Push
to set the initiate layer to Continuous OFF. The Product is now in the
Idle state. Push to start the measurement sequence.
Details of the Trigger subsystem in this example: When is pushed, the
triggering process leaves the Initiate layer, passes through the two ARM layers
(which are each set to Immediate by default) and enters the Trigger layer. As the
event is set to Immediate (default), there is no need for a discrete event to occur
and the process moves downwards to the delay block. After the 20 second delay
the process continues downwards and the acquisition is triggered.
Holdoff: This causes the Trigger layer to pause for the set time after an
acquisition is initiated. This allows the acquisition to complete before the system
becomes available to accept the next trigger. The default Holdoff setting is Auto,
which allows the acquisition to complete before the system becomes available to
accept the next trigger in any given function and range. For most cases, leaving
Holdoff in Auto is recommended, to prevent “Trigger too fast” errors. Holdoff can
be set manually to between 0 seconds and 100 seconds; setting Holdoff to 0
seconds can yield the fastest measurement rate. Holdoff is not available in the
Arm2 and Arm1 layers.
An example of using Holdoff would be if the Trigger layer event is set to External
and triggers are being divided with ECount greater than 1. In the example using
ECount above, the required read rate is 2 MHz. ECount is set to five to divide
triggers by five. The Trigger layer cycle time must be less than 500 ns. The
acquisition time is 400 ns so Holdoff must be set to less than 100 ns.
Note
At first glance it may seem the Delay example or the ECount
examples above could be achieved with just using trigger Holdoff. In
the case of Delay, this would not work correctly because Holdoff is
implemented after the acquisition was triggered, while Delay occurs
before the acquisition. It would seem the ECount would work if
Holdoff was set appropriately but this is not a good alternative as
Trigger too Fast errors could be reported if the Holdoff time was not
exactly matched to the 10 MHz clock input.
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