Transcript hardware testing of digital input & output cards for data

HARDWARE TESTING OF DIGITAL INPUT &
OUTPUT CARDS FOR DATA ACCUSITION &
CONTROL SYSTEMS
A Mini Project Report submitted in partial fulfillment
for the award of the degree
Bachelor of Technology in Electronics and
Communication Engineering
Submitted by
GAURAV BHATNAGAR
(06621A0467)
VENKATESWARAN SREERAM
(06621A04B8)
Chapter 1: Introduction
• 1.1 DIGITAL INPUT AND OUTPUT CARDS:
• Digital I/O devices process digital signals and the output
results in digital format. A digital I/O module has both
input and output functionality and is used for data
acquisition. This module includes on-off signals used in
communication, user interface, or control. It provides
integrated signal conditioning, reduction in wiring/cabling
requirements and ease of installation. A digital I/O card is
a specially made device for automation and control of
industrial equipment, and is usually used in machine
vision and automation applications. Digital I/O devices
can be designed and manufactured to meet most
industry specifications.
DATA ACQUISITION AND
CONTROL SYSTEMS
• It generally refers to an industrial control system: a computer system
monitoring and controlling a process. The process can be industrial,
infrastructure or facility based as described below:
• Industrial processes include those of manufacturing, production,
power generation, fabrication, and refining, and may run
.
continuous,batch, repetitive, or discrete modes
• Infrastructure processes may be public or private, and include water
treatment and distribution, wastewater collection and treatment, oil
and gas pipelines, electrical power transmission and distribution,
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civil defense siren systems, and large communication systems
Functionality of Digital Input Card
(DI)
• 2.1 FEATURES OF THE DIGITAL INPUT CARD
• It has 8 channels.
• It has 8 inputs and 8 outputs.
• Each channel is optically isolated from
each other.
• Operating voltage is +17 to +28 V.
• It supports 8 relay output / transistor
output channels.
• The DI8 is an 8 channel isolated digital input board. The
optically isolated inputs of the DI8 consist of a dual
channel OPTO-coupler with a resistor for current limiting.
The DI8 can be used to sense DC signals from TTL
levels up to 24Vand to isolate the computer from large
common-mode voltages, ground loops and voltage
spikes that often occur in industrial environments.
• The output signal from the opto- coupler is given to the
bounce eliminator which removes the flickering effect
caused due to the electro-mechanical nature of the relay.
• Diagram for 8 channel data input card
OPTO-COUPLER
• In electronics, an opto-isolator (or optical isolator, optocoupler, photo
coupler, or photoMOS) is a device that uses a short optical
transmission path to transfer a signal between elements of a circuit,
typically a transmitter and a receiver, while keeping them electrically
isolated — since the signal goes from an electrical signal to an
optical signal back to an electrical signal, electrical contact along the
path is broken. The opto-isolator is simply a package that contains
both an infrared LED and a photo detector such as silicon diode,
transistor Darlington pair, or SCR. The wave-length response of
each device is tailored to be as identical as possible to permit the
highest measure of coupling possible. The opto-coupler that is used
in the DI8 card is the
APPLICATIONS
• 1) Opto couplers are used to isolate low-current control
or signal circuitry from transients generated or
transmitted by power supply and high-current control
circuits. The latter are used within motor and machine
control function blocks.
• 2) Medical equipment often uses opto couplers.
• 3) Where electrical safety is paramount, opto-couplers
can totally isolate circuitry which may be touched by
humans from mains electricity
• 4) Opto-isolators can help cut down on ground loops,
block voltage spikes, and provide isolation
BOUNCE ELIMINATOR
• The bounce eliminator which is commonly used in the
DI8 input card is the MC 14490.It is also called as MC
14490 Hex Contact Bounce Eliminator. It is a 16 pin
device.
• The MC 14490 is constructed with complementary MOS
enhancement mode devices, and is used for the
elimination of extraneous level changes that result when
interfacing with mechanical contacts. The digital contact
bounce eliminator circuit takes an input signal from a
bouncing contact and generates a clean digital signal
four clock periods after the input has stabilized. The
bounce eliminator circuit will remove bounce on both the
"make" and the "break" of a contact closure
Features of bounce eliminator
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Diode Protection on All Inputs
Six Debouncers Per Package
Internal Pull-ups on All Data Inputs
Can Be Used as a Digital Integrator, System Synchronizer, or Delay
Line
Internal Oscillator (R-C), or External Clock Source
TTL Compatible Data Inputs/Outputs
Single Line Input, Debounces Both "Make" and "Break" Contacts
Cascadable for Longer Time Delays
Schmitt Trigger on Clock Input (Pin 7)
Supply Voltage Range = 3.0 V to 18 V
Pb-Free Packages are Available