Measurement Computing Data Acquisition Systems rev.10.4 - Manual (Page 306)

Setting the Trigger Level
The level parameter is used for those trigger types who depend on an input channel comparison to detect the
trigger start or stop event. The level parameter is a single precision floating point value which represents, in
engineering units, the level at (or around which) the trigger event should be detected. The actual level at which the
trigger event is detected depends upon trigger sensing and variability discussed later. Below is a table describing the
various ranges of possible values for the level paramter based on the trigger source:
Trigger Level Settings
Trigger/Stop Sources
(daqAdcTriggerSource)
Meaning of level parameter
DatsSoftwareAnalog (P1) Voltage or temperature (in degrees C) at which the trigger level is to be defined. Trigger detection
performed in software.
DatsHardwareAnalog (P1) Voltage or temperature (in degrees C) at which the trigger level is to be defined. Trigger detection
performed in hardware.
DatsDigPattern (P2/P3) Defines bit pattern for the digital channel trigger. The valid values are:
0.0 (no bits set) - 255.0 (all bits set) for 8-bit digital channel banks (P2)
0.0 (no bits set) – 65,535.0 (all bits set) for 16-bit channel banks (P3)
DatsCounter (P3) Pulse or Totalize counter values (0.0 – 65,535)
DaqBooks, TempBooks, DaqBoard (ISA) and Daq PC Cards have a fixed hardware based
hysteresis value, so the variance parameter is ignored for those devices when using with
DatsHardwareAnalog
trigger source.
Setting the Trigger Sensitivity
Some trigger sources require a trigger sensitivity setting. The trigSensitivity setting is only required for
trigger sources which are based upon an input signal. The trigger sensitivity normally defines the way in which a
trigger event is detected based upon the characteristics of the trigger input signal. Often, it defines the way in which
the trigger input signal(s) should be compared to the trigger level parameter value.
Setting the Trigger Variance
While the trigSense parameter indicates the direction of the input signal relative to the level parameter, the
variance
parameter specifies the degree to which the input signal can vary relative to level parameter. The
variance parameter is a single-precision floating point value which represents, in engineering units, the amount
that the trigger event can vary from the level parameter.
4.6-28 Daq API Command Reference
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Programmer’s Manual