National Instruments 321645c-01 用户手册

Chapter 2

Function Reference — Config_Alarm_Deadband

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 National Instruments Corporation

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NI-DAQ FRM for PC Compatibles

alarmOnMessage and alarmOffMessage are messages you define. When the alarm-on 
condition occurs, NI-DAQ passes alarmOnMessage back to you. Similarly, when the 
alarm-off condition occurs, NI-DAQ passes alarmOffMessage back to you. The messages 
can be any value.

In Windows, you can set the message to a value including any Windows predefined messages 
such as 

WM_PAINT

. However, to define your own message, you can use any value ranging 

from 

WM_USER 

(0x400) to 0x7fff. This range is reserved by Microsoft for messages you 

define.

callbackAddr is the address of the user callback function. NI-DAQ calls this function when 
DAQEvent occurs. See 

Config_DAQ_Event_Message

 for restrictions on this parameter.

To meet the high alarm-on condition, the input signal must first go below 
(trigLevel - deadbandWidth/2) volts and then go above (trigLevel + deadbandWidth/2) 
volts. On the other hand, to meet the high alarm-off condition, the input signal must first go 
above (trigLevel + deadbandWidth/2) volts and then go below 
(trigLevel – deadbandWidth/2) volts. See Figure 2-1 for an illustration of the high alarm 
condition.

Figure 2-1.  High Alarm Deadband

The low alarm deadband trigger condition is the opposite of the high alarm deadband 
trigger condition. To meet the low alarm-on condition, the input signal must first go above 
(trigLevel + deadbandWidth/2) and then go below (trigLevel - deadbandWidth/2). On 
the other hand, to meet the low alarm-off condition, the input signal must first go below 
(trigLevel – deadbandWidth/2) and then go above (trigLevel + deadbandWidth/2). 
See Figure 2-2 for an illustration of the low alarm condition.

on

off

On:  high alarm on
Off:  high alarm off

Time