National Instruments Welding System 321645c-01 Manual De Usuario

Chapter 2

Function Reference — GPCTR_Set_Application

NI-DAQ FRM for PC Compatibles

2-220

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 National Instruments Corporation

until (counter_armed = ND_NO)

GPCTR_Watch(deviceNumber, gpctrNumber, ND_COUNT, counted_value)

To calculate the measured interval, you need to multiply the counted value by the period 
corresponding to the timebase you are using. For example, if your 

ND_SOURCE 

is 

ND_INTERNAL_20_MHZ

, the interval will be 1/(20 MHz) = 50 ns. If the 

ND_COUNT

 is 4, 

(Figure 2-15), the actual interval is 4 * 50 ns = 200 ns. 

When the counter reaches terminal count (see Table 2-31), it rolls over and keeps counting. 
To check if this occurred, use the 

GPCTR_Watch

 function with entityID set to 

ND_TC_REACHED

. 

Typically, you will find modifying the following parameters through the 

GPCTR_Change_Parameter

 function useful when the counter application is 

ND_SINGLE_PERIOD_MSR

. You can change the following:

•

ND_SOURCE

 to 

ND_INTERNAL_100_KHZ

. With this timebase, you can measure the time 

interval between 20 µs and 160 s for E Series and 445X (24 bits) devices and a time 
interval of 20 

µ

s and 11.37 hours for 6602 and 455X devices (32 bits). The resolution will 

be lower than if you are using the 

ND_INTERNAL_20_MHZ

 timebase. 

•

ND_SOURCE_POLARITY

 to 

ND_HIGH_TO_LOW

.

•

ND_GATE

 to any legal value listed in the 

GPCTR_Change_Parameter

 function 

description.

•

ND_GATE_POLARITY

 to 

ND_NEGATIVE

. The interval will be measured from a 

high-to-low to the next high-to-low transition of the gate signal. 

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

. 

To provide your timebase, you can connect your timebase source to one of the PFI pins on the 
I/O connector and change 

ND_SOURCE

 and 

ND_SOURCE_POLARITY

 to the appropriate values. 

You also can configure the other general-purpose counter for 

ND_PULSE_TRAIN_GNR

 and set 

ND_SOURCE

 of this counter to 

ND_OTHER_GPCTR_TC

 to measure intervals longer than the 

interval timebases allow. 

ND_SINGLE_PULSE_WIDTH_MSR

In this application, the counter is used for a single measurement of the time interval between 
two transitions of the opposite polarity of the gate signal. By default, the measurement 
is performed between a low-to-high and a high-to-low transition on the default I/O 
connector gate pin (refer to 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. For the E Series and 445X devices with counter width of 24 bits, you can