Advantech iDAQ-817, User Manual

Page: 24 / 36

iDAQ-817_821 User Manual 14
Figure 3.4 Start and stop of the analog input acquisition with delay.
Buffered analog input acquisition has several advantages over instant analog input
acquisition:

The start and stop time of acquisition (or duration of the acquisition) can be pre -
cisely controlled by hardware trigger signals.

The ADC conversion rate is configurable and the sample rate can be much
higher by using hardware sample clock signals.

Time between samples is deterministic.
3.2.3 High Common-Mode Amplifier
Each channel is equipped with a high common-mode voltage amplifier that can with -
stand high common-mode input voltage. Common-mode input voltage (VCM) is the
ground voltage difference between the source and the device as shown in Figure 3.5.
Figure 3.5 Common-mode input voltage.
This is suitable for applications which measure voltages with high common-modes
such as battery cell voltage monitoring, high-voltage current sensing, or power-sup -
ply current monitoring. For other analog input measurement devices without this fea -
ture, the device will be damaged due to the high common-mode input voltage. Refer
to the device specifications for the maximum allowable common-mode voltage.
3.2.4 Analog Input Low-pass Filter
The low-pass filter removes high frequency noise of the input signal and the noise
that is added by the high common-mode voltage amplifier. It can also act as an anti-
aliasing filter which avoids alias generation due to ADC conversion.