User manual

11 Chapter 3
External Trigger Source Connection
In addition to pacer triggering, the PCI-1715U card also allows external
triggering for A/D conversions. A low-to-high edge coming from
EXT_TRG will trigger an A/D conversion on the PCI-1715U board.
Note: Please ascertain that turn on your external trigger source and con-
nect it to "EXT_TRG" BEFORE acquire analog input signals.
Note:Don't connect any signal to the EXT_TRG pin when the external
trigger function is not being used.
Note: If you use external triggering for A/D conversions, we recommend
you choose differential mode for all analog input signals, so as to reduce
the cross-talk noise caused by the external trigger source.
Note: Charge Injection Error
A small electric charge will be produced every time when a multiplexed
data-acquisition device switched channels, and consequently creates a
small voltage drop across that output impedance, which makes the mea-
sured voltage different than its actual value, namely the charge injection
error.
To minimize the charge injection errors, a signal source/ sensor with the
low impendence is recommended, or using a op amplifier connecting to
the signal source can also effectively lower the charge injection errors.