National Instruments Welding System 321645c-01 Manuale Utente
Chapter 2
Function Reference — GPCTR_Set_Application
NI-DAQ FRM for PC Compatibles
2-218
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National Instruments Corporation
The following pseudo-code continuation of the example given earlier illustrates what
you can do to read the counter value continuously (
you can do to read the counter value continuously (
GPCTR_Watch
function with
entityID =
ND_COUNT
does this) and print it:
Repeat Forever
{
GPCTR_Watch(deviceNumber, gpctrNum, ND_COUNT, counterValue)
Output counterValue.
}
When the counter reaches terminal count (TC), it rolls over and keeps counting. To check if
this occurred, use
this occurred, use
GPCTR_Watch
function with entityID set to
ND_TC_REACHED
. Refer to
Table 2-32 for TC for E Series, 445X, 455X, and 6602 devices.
Typically, you will find modifying the following parameters through the
GPCTR_Change_Parameter
function useful when the counter application is
ND_SIMPLE_EVENT_CNT
. You can change the following:
•
ND_SOURCE
to any value
•
ND_SOURCE_POLARITY
to
ND_HIGH_TO_LOW
•
ND_INPUT_CONDITIONING
(6602 and 455X devices only) to any value.
You can use the
GPCTR_Change_Parameter
function after calling
GPCTR_Set_Application
and before calling
GPCTR_Control
with
action =
ND_PROGRAM
or
ND_PREPARE
.
application =
ND_SINGLE_PERIOD_MSR
In this application, the counter is used for a single measurement of the time interval between
two transitions of the same polarity of the gate signal. By default, the events are low-to-high
transitions on the default gate connector pins (see Table 2-25). The counter counts the 20 MHz
internal timebase (
two transitions of the same polarity of the gate signal. By default, the events are low-to-high
transitions on the default gate connector pins (see Table 2-25). The counter counts the 20 MHz
internal timebase (
ND_INTERNAL_20_MHZ
), so the resolution of measurement is 50 ns. The
counter counts up starting from 0.
With the default 20 MHz timebase, combined with the counter width (24 bits), you can
measure a time interval between 100 ns and 0.8 s long. For the 6602 devices with counter
width 32 bits, you can measure a time interval between 100 ns and 214 s long.
measure a time interval between 100 ns and 0.8 s long. For the 6602 devices with counter
width 32 bits, you can measure a time interval between 100 ns and 214 s long.
Table 2-32. Terminal Count
E Series and 445X Devices
6602 and 455X Devices
2
24
– 1
2
32
– 1