The Industrial Feature Set: Change Detection

This document is part of a comprehensive tutorial on industrial Digital I/O and Counter/Timer hardware. Learn about National Instruments product offerings for digital and timing I/O, the Industrial Feature Set including watchdog timers and isolation, complementary devices like relays, solenoids and encoders, concepts like sinking and sourcing, and see how these devices can be used in your industrial application.

For more information return to the Complete Industrial Digital I/O and Counter/Timer Tutorial

What is Change Detection?

With change detection, you can automatically trigger your software application to perform a digital read operation upon a digital change of state. Change Detection allows you to monitor for digital events with minimal processor usage.

Recommended Products that Feature Change Detection

NI 6509
NI 6514
NI 6515
NI 6528

How Change Detection

The digital I/O module notifies the software application when this event occurs. No polling is necessary, since the digital I/O module generates an interrupt to automatically "wake up" your application.

Creating a program to use change detection is simple in NI-DAQmx. You can configure your change detection application using the NI DAQ Assistant (figure 1). The NI-DAQmx Timing VI has a new polymorphic instance that treats Change Detection just like any other buffered NI-DAQmx input operation (figure 2). The programmer has complete control over which lines are used to detect a change. The Rising Edge Lines and Falling Edge Lines control can be populated with any combination of input lines that physically exist on the device. The next section discusses how change detection is even more useful when used with digital input filtering.



Figure 1: Configuring Change Detection using NI DAQ Assistant



[+] Enlarge Image
Figure 2: Configuring Change Detection using NI-DAQmx VIs

Reader Comments | Submit a comment »