Signametrics
20
2.11 Trigger Functions
2.11.1 External Hardware Trigger (at DIN-7 connector)
Trigger Input voltage level range
+3 V to +15 V activates the trigger.
Minimum Trigger Pulse Width
1/Ap 50
S
Minimum trigger input current
1 mA
Internal Reading Buffer
Circular; 80 or 120 readings depending on resolution.
Edge
Selectable positive or negative edge.
Isolation of trigger input
±50 V from analog DMM inputs, and from chassis
earth ground.
2.11.2 Analog Threshold Trigger
Trigger point:
Selectable positive or negative transition of set threshold.
Buffer type:
Circular
Captures:
up to 120 post-trigger readings for apertures < 625uSec.
Captures:
up to 80 post-trigger readings for apertures > 625uSec.
Aperture range:
160ms to 625
S (to 2.5
S with SMU2064)
Read Interval
range
:
1/Aperture to 65ms
Post-Trigger readings:
Selectable from 0 to buffer size.
Pre-trigger readings:
Selectable from 0 to buffer size.
Triggered Sample:
Retrievable from DMM.
2.11.3 Long Trigger (SMU2064 with Option ‘R’)
Trigger point:
Positive edge on selected trigger source (PXI or DIN-7)
Trigger Pulse Width:
Minimum 50
s
Samples per Trigger event:
1 to 50,000
Number of Triggers:
1 to 50,000
Sample to Sample delay:
100
s to 3,600s
Aperture range:
160ms to
2.5
S
Read Interval:
Must be set to zero
2.11.4 Delayed Hardware Trigger
This function allows time for the signal to settle after a trigger has occurred.
It allows readings to be delayed up to 65mSec with 1
Sec resolution
.
It allows readings to be delayed up to 1s with 2
s resolutions.
2.12 Measurement Times
2.12.1 Measurement Apertures and Read Interval
Both Aperture and The Read Interval may be set. The range of values depends on the DMM model and its
mode of operation. For example, when using the internal buffer such as in External Trigger mode, the
Read Interval can be set smaller than in Command/Response operation. The time involved in processing
the measurement command and the post processing and transmission of the measurement constitute an
overhead, which limits the minimum Read Interval to a value that is greater than the Aperture. Setting it
to zero, the default, results in fastest measurement rates. The faster SMU2064 has lower overhead and
therefore a shorter minimum Read Interval than the SMU2060. For instance, with Aperture set to 625us
and Read Interval set to zero, in command/response operation the SMU2060 measurement rate is about
1,090/s while that of the SMU2064 is 1,370/s. This indicates overhead of about 300µs for the SMU2060
and 100µs for the SMU2064. Another method of setting the Aperture is by use of the DMMSetPLC(),
which sets the aperture to a multiple of the power line cycle.
The SMU2064 has 31 apertures, and the SMU2060 has 30 available. The following table lists all
available measurement apertures and the corresponding minimum read time (including data transfers
overhead etc..) and measurement rates for the various operations DMMRead(), DMMReadNorm(),
DMMReadNsamples() and triggered operaton.