User manual

Chapter 3 Software Overview
NI-DAQ User Manual for PC Compatibles 3-88 ni.com
Figure 3-33. Frequency Measurement
For 16-bit resolution event counting and pulse width, time-lapse, or
frequency measurement, you only need one counter. Select cont =0so
that you are notified if the counter overflows (see the
CTR_EvRead
and
CTR_EvCount
function descriptions in the NI-DAQ Function Reference
Online Help file). If cont = 1, event counting continues when the counter
rolls over and no overflow condition is registered. cont = 1 is useful when
more than one counter is concatenated for event counting.You can use any
gating mode. In addition, select TC toggled output type and positive output
polarity during the
CTR_Config
call so that overflow detection works
properly.
For greater than 16-bit resolution, you can concatenate two or more
counters. Configure a low-order counter to count the incoming edges or
to measure the incoming pulse. Connect the OUT signal of the low-order
counter to the SOURCE input of the next high-order counter by specifying
a timebase of 0 for the next high-order counter. Configure the next
high-order counter to count once every time the low-order counter rolls
over. You can connect the OUT signal of the next high-order counter to the
SOURCE input of an additional counter. The last counter (referred to as
the high-order counter) will perform overflow detection. The lower order
counters increment continuously and generate output pulses when they
roll over.
SOURCE
Periodic Signal
GATE
Known Pulse
CTR_EvRead Count
Frequency
1
2344
4/t1
t1