Omega OMB-DAQBOARD-3000 User Manual

Appendix B 

907994

 

Hardware Analog Level Trigger     B-1 

Issue:  
 
When the starting out analog input voltage is near the trigger level, and you are performing a rising 
[or falling] hardware analog level trigger, it is possible that the analog level comparator will have 
already tripped, i.e., to have tripped before the sweep was enabled. If this is the case, the circuit will 
wait for the comparator to change state.  However, since the comparator has already changed state, 
the circuit will not see the transition. 
 

Solution:   
 
(1) Set the analog level trigger to the desired threshold.  
 
(2) Apply an analog input signal that is more than 2.5% of the full-scale range away from the 

desired threshold. This ensures that the comparator is in the proper state at the beginning 
of the acquisition. 

 
(3) Bring the analog input signal toward the desired threshold. When the input signal is at the 

threshold (± some tolerance) the sweep will be triggered.  

 
(4) Before re-arming the trigger, again move the analog input signal to a level that is more  

than 2.5% of the full-scale range away from the desired threshold. 

 

 
 
 
Example:  

 

o

  an engineer is using the ±2V full-scale range (gain = 5) 

o

  he desires to trigger at +1V on the rising edge 

o

  he sets the analog input voltage to an initial start-value which is 

less than  +0.9V (1V – (2V * 2 * 2.5%)).