Keithley KPCI-3110, Руководство пользователя

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KPCI-3110 and KPCI-3116 User’s Manual Functional Description 2-11
perform the following steps to configure a scan triggered by an external analog trigger input
signal:
1. Specify the trigger source as either a rising-edge or falling-edge analog threshold trigger.
2. Specify channel 0 as the trigger channel. To distinguish this channel from analog input channel
0, set the special gain code of &H8000 to indicate the use of the dedicated Analog Trigger line.
When channel 0 is scanned, the analog trigger signal at TB107 is detected to start the acquisition
process.
•
One of the analog input channels after gain is applied (also called the output of the pro-
grammable gain amplifier (PGA). Using software, specify the trigger source as either a posi-
tive threshold trigger or negative threshold trigger.
Using DriverLINX software, specify the analog input channel used as the analog threshold trig-
ger as the first channel in the channel list; refer to
page 2-3 for more information.
On KPCI-3110 and KPCI-3116 boards, the threshold level is set using a dedicated 8-bit DAC;
the hysteresis is fixed at 50mV. Using software, program the threshold level by writing a voltage
value to this DAC; this value can range from
−
10V to +10V.
NOTE If you are using an analog threshold trigger to trigger both the A/D and
the D/A subsystems, ensure that you use the same analog trigger type for
both subsystems (either external or one of the analog input channels).
Trigger acquisition modes
KPCI-3110 and KPCI-3116 boards can acquire data in post-trigger mode, pre-trigger mode, or
about-trigger mode. These trigger acquisition modes are described in more detail in the follow-
ing subsections.
Post-trigger acquisition
Use post-trigger acquisition mode (continuous mode) when you want to acquire data when a
post-trigger or retrigger, if using triggered scan mode, occurs.
Using DriverLINX software, specify the following parameters:
•
The dataflow as continuous.
•
The trigger source to start the post-trigger acquisition (the post-trigger source) as any of the
supported trigger sources.
Refer to page 2-7 for more information on the supported conversion modes. Refer to page 2-10
for information on the supported trigger sources.
Post-trigger acquisition starts when the board detects the post-trigger event and stops when the
specified number of post-trigger samples has been acquired, or when you stop the operation.
If you are using triggered scan mode, the board continues to acquire post-trigger data using the
specified retrigger source to clock the operation. Refer to
page 2-8 for more information on trig-
gered scan mode.
Figure 2-3 illustrates continuous post-trigger mode using a channel-gain list with three entries:
channel 0, channel 1, and channel 2. Triggered scan mode is disabled. In this example, post-trigger
analog input data is acquired on each clock pulse of the A/D sample clock. The board wraps to the
beginning of the channel-gain list and repeats continuously (continuously-paced scan mode).
Figure 2-3
Continuous post-trigger mode without triggered scan
Post-trigger Event Occurs
Chan 0
Chan 1
Chan 2 Chan 0
Chan 1
Chan 2 Chan 0
Chan 1
Chan 2 Chan 0
Chan 1
Chan 2
A/D
Sample
Post-trigger Data Acquired Continuously