Measurement-computing Data Acquisition Systems rev.10.4 Manuel d'utilisateur télécharger pdf (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.

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Measurement-computing Data Acquisition Systems rev.10.4 Manuel d'utilisateur Page 306