Digital Output Sensors

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.

Introduction to Digital Output Sensors

A Digital Output Sensor will produce only two values in its output, either on or off, as opposed to an Analog Output Sensor which produces a continuously varying output value over its entire range. The simplest example of a digital sensor is the touch switch. A typical touch switch is an open circuit with infinite resistance when it is not pressed and a short circuit with zero resistance when it is pressed.

Recommended NI Products that Connect to Digital Output Sensors

Digital I/O Boards	Counter/Timer Boards
NI 6509	NI 6601
NI 6514	NI 6602
NI 6515	NI 6608
NI 6528	NI 6624

Technical Overview

Nowadays, you can find sensors that produce trains of transitions between the On and Off state. With these types of sensors the frequency, time interval, duty cycle or the number of pulses convey the sensor’s measurement.

Figure 1 shows a classification of digital output sensors based on signal characteristics driving its output. As can be seen in the chart, 45 % of the digital output sensors are based on the on-off state of the digital line, 35 % of the sensors are based on the frequency of the signal and 12 % as based on the duty cycle of the output frequency 2.


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Figure 1: Digital Output Sensors
(Kirianaki, Yurish, Shpak, Deynega. Data Acquisition and Signal Processing for Smart Sensors, 2002 [ISBN 0-470-84317-9])

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