National Instruments Welding System 321645c-01 Manual De Usuario

Chapter 2

Function Reference — Configure_HW_Analog_Trigger

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 National Instruments Corporation

2-87

NI-DAQ FRM for PC Compatibles

If you set trigSource to 

ND_THE_AI_CHANNEL

, you can use the signal connected to one of 

the analog input pins for triggering. In this case, the signal is amplified on the device before 
it is used for trigger generation. You can use this source selection under the following 
conditions:

•

You want to perform data acquisition from a single analog input channel (the 

DAQ

 family 

of functions). You only can use the channel you are acquiring from for analog triggering.

•

You want to perform data acquisition from more than one analog input channel 
(a combination of the 

DAQ

 and 

SCAN

 families of functions). The only analog input 

channel you can use as the start trigger is the first channel from your list of channels. You 
cannot use this form of the analog trigger for the stop trigger in case of pretriggered data 
acquisition. 

•

You do not want to perform any analog input operations (the 

AI

, 

DAQ

, and 

SCAN

 families 

of functions). You must use 

AI_Setup

 to select the analog input channel you want to use 

and the gain of the instrumentation amplifier. You also can use 

AI_Configure

 to alter 

the configuration of the analog input channel. 

•

You want to use 

AI_Check

, and you want to use the analog trigger for conversion timing. 

You do not have to perform any special steps.

The reason for using these constraints is that if you are scanning among several analog input 
channels, signals from those channels are multiplexed in time, and the analog triggering 
circuitry is unable to distinguish between signals from individual channels in this case.

For DSA devices only, any of the analog input channels can be the source of the analog 
trigger, even channels that are not part of the channel list set in 

DAQ_Start 

or

 SCAN_Setup

. 

Set  trigSource to the channel number of the channel to monitor for the analog trigger.

When you use this function, you activate the onboard analog triggering hardware. 
This onboard hardware generates a digital trigger that the DAQ-STC then uses for timing and 
control. To use the analog trigger, you need to use this function and the 

Select_Signal

 

function. To use analog triggering, use as much hysteresis as your application allows because 
the circuitry used for this purpose is very noise-sensitive.

For E series devices, when you use 

Select_Signal

, set source to 

ND_PFI_0

 for your 

signal, and set sourceSpec as appropriate. Notice that the two polarity selections give you 
timing control in addition to the five triggering modes listed here. For DSA devices, when you 
use 

Select_Signal

, set source to 

ND_ATC_OUT

 for your signal, and set sourceSpec to 

ND_DONT_CARE

. NI-DAQ will route the analog trigger circuit output as appropriate for the 

device.