Filter
Top Products
5
.
2
.
2
.
9
Analog Trigger Threshold
The analog trigger threshold can only be set by the output of D/A channel 1, with an
equivalent range from -10V to +10V (full A/D converter input range). The threshold level is
set at the A/D converter input (after the programmable gain amplifier), not the one at the
input connector (before the PGA). The following formula is used to convert the code value
(C/-2048 to 2047) written into D/A channel 1 to the trigger level set against the analog input
voltage (U) for the selected A/D input channel:
U = (C/2048) * (10/G)
where U is in volts and G is the internal gain of the selected analog input channel. In the case
of an expansion card, further calculation can be performed by converting the value of U
obtained above with the transfer function of the expansion card. There is a fixed hysteresis of
about 10 mV in the analog comparator circuit used for generating the analog trigger. The
accuracy of the analog trigger level is typically 1% of the A/D input range (±10v), or within
±0.1v.
The selected analog input channel is always the one specified as the first entry of the scan list
queue (the one with the first channel mark set to “1”). However, this is not the case with the
pre-trigger option. After receiving the arm command, the A/D converter is already scanning
the analog input channels specified in the scan list. The analog comparator generates an
analog trigger any time it’s input passes through the trigger threshold. For example, if one of
the input channels specified in the scan list is below the threshold while another is above it,
the trigger is generated because the analog comparator input passes through the threshold in
either direction during channel scanning. The following conditions must both be met to use
the analog trigger with pre-trigger option selected: (1) The input channels specified in the scan
list must be either all below or all above the analog trigger threshold before the trigger event
occurs. (2) When the trigger event occurs, at least one of the input channels passes across the
threshold in either direction and at least one input channel stays on the original side.
DAQP-208/208H/308 Users Manual 47