5.4 Triggering
Triggering controls an acquisition cycle. Once the system is armed, a trigger is required to collect the data.
The user must determine the triggering requirement based on the nature of the measurement and the amount of data needed to satisfy the system’s purpose. The trigger source can be a software command or an analog input channel on reaching a specified voltage level can be used to trigger the system.
IMMEDIATE
START TIME
CHANNEL VALUE - RISING
-FALLING TRIGGER EVENT
POST-TRIGGER SCAN COUNT
SCAN GROUP
TIME
SCAN PERIOD 
Figure 5-2. Trigger Source Diagram
5.5 Signal Modes
OM-DAQ-USB-2401 units operate in one of two modes, (1) single-ended mode, or (2) differential mode. These terms (single-ended mode and differential mode) apply to their use in this manual. In other sources these terms may be used in a different manner.
Choosing between differential and single-ended inputs is made by software command. The following text briefly describes the two signal modes.
Single-ended mode refers to a mode, or circuit set-up, in which a voltage is measured between one signal line and common ground voltage (Vcm). The measured voltage may be shared with other channels. The advantage of a single- ended non-differential mode [over differential mode] is that it provides for a higher channel count, for example: 16 channels instead of 8.
NOTE:
In DAQ applications, thermocouples should not be connected single-ended. Doing so can result in noise and false readings. This is especially true when acquiring other high-amplitude signals in conjunction with thermocouple signals that are connected single-ended.
