Describe
the Key SCADA System.
The Key SCADA (Supervisory Control and Data Acquisition)
system consist of five major
components, Master Computer, Software, Communication Link, Remote Terminal and Signal
Transducers. These components plus options permit Key to assembly a SCADA system to
meet your specific requirements. Our free assistance in equipment selection will
assure you of
the best system to meet your needs. In most applications a
complete system may consist of two
Remote Terminals connected back to back. The Personal Computer
may be replaced by a
Display Panel with lamps, push buttons and digital displays.
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What will the Key system do for
me ?
One obvious advantage of telemetry is eliminating the need for
driving across town to check on, or change, the status of equipment operating at
remote locations. Telemetry also allows the utility to discover alarm conditions before they
become critical events. You can monitor alarm conditions occurring at remote sites in "real time."
Another advantage of telemetry is in preventive maintenance. By utilizing the
reports provided by Master Computer Software, the utility can diagnose problems
long before they become failures. These reports allow the user to compare run
times of equipment from day to day. These run times normally are very constant, so a
variation in run times can indicate a problem.
Another valuable use of radio telemetry is being able to relay system status
across town to initiate automatic control functions. The system can transmit
status such as "pump run," "tank level," or "water
pressure" from one remote location to another to activate control functions
such as turning on chlorine injectors, or turning off well field pumps.
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What does Key recommend for the
Master Computer ?
The Master Computer is usually a standard Personal Computer (PC)
with monitor, printer etc. permitting the operator to monitor and control the field
data. The PC serial port is connected to a suitable modem for communication with the
Remote Terminals. The PC may drive a local printer, alarms, charts or other
devices
through one or more of its output ports. All cables and
drawings are supplied with your system, assuring a seamless installation using
non-technical
personnel. |
Tell me about the Master Program.
The PC programming varies widely from simple no cost canned programs for
monitoring, to complex software written to your specifications. These programs are written
in MicroSoft Visual Basic. Call me, Brent Hazelwood, I will be glad to
discuss
your application with no obligation to purchase. |
What is a Remote Terminal Unit ?
A Remote Terminal (RTU), usually located at a field location, converts the
analog values,
discrete,
and counter signals into a serial digital format. This permits all signals to be
transmitted on a
single telephone pair or radio circuit. The RTU consist of a small computer, modem, signal
converters
and
a non-interruptible power supply. The RTU options include modem type,
clock-calendar,
additional Input-Output (I/O) signals and housing. |
How does the Master communicate
with the Remote Terminals ?
You may select one or mix of several means of communication. They are leased
telephone lines, standard dial up telephone lines, cellular telephones, or UHF-VHF radio.
Your selection will be based primarily on cost and circuit availability.
Leased Lines are reliable
and require less initial investment in equipment. If data is
required in real time, perhaps every few minutes, the leased line is often specified.
There
is a monthly fee for the line use, charged in ¼ mile increments. The Bell
compatible
202
Modem is the industry standard for these circuits. Key
manufactures a full
line of 202
modems for both the Remote Terminals and Master Station.
Dial Up Lines
are well suited
when the data needs to be accessed less often. Again the
investment in equipment is low and the telephone rates are about
$50.00 per
month for each
site, plus long distance charges. The modem used here is the CCITT standard, the
same
unit that is supplied in virtually every
personal
computer. Key uses an off the shelf unit for
the Master site
and has a built-in modem for the Remote
Terminal.
VHF-UHF Radio requires the investment of a
transmitter-receiver and antenna for each
site, however there is no monthly
fees. Distances are normally limited to line-of-site from antenna to antenna. If the cost is justified repeaters
may be added.
If you are eligible a
system licensed by the FCC may be your best selection.
Spread Spectrum non-licensed
frequencies are also available. Radio communication is often simple and
straight forward, however it may become complex and require a system study.
Contact me,
Brent Hazelwood, for a free evaluation. |
What does Analog Input or Output
mean ?
The Analog Input Signal indicates the value of a function being measured.
Some
examples are pressures, liquid level, power etc. A device called a "Transducer"
or "Transmitter" is used to convert the measured function into a current or
voltage that varies in direct proportion to its input value. The industry standard is 4-20
Milliamperes (mA), however other values are often
used. A typical Transducer might output 4 mA for zero pressure and 20 mA for 500 lbs. The
Key Remote Terminal Units (RTU) fully support the value you specify. Analog
output
signals are also usually 4-20 mA and they are used to remotely control
devices that require
an incremental adjustment or a variable set-point.
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Describe Discrete Input and
Output.
Discrete or Digital input indicates the status of a single wire circuit. It is
normally connected to
a switch, relay or other device with electrical contacts. These are used
to
indicate an Alarm,
On/Off, Open/Close, Stop/Run etc. Discrete Output is used to
drive
external relays, solenoids
etc. You may remotely control valve position, lights,
Stop-Start
engines or any other equipment
that can be controlled by relay contacts. |
What is the function of a counter
input ?
The counter measures the frequency or totalized value of a string of pulses or contact
closures. This might be useful to measure RPM, turbine meters, part count etc. |
What is RS-232 ?
RS-232 or Serial Communication is an IEEE industry standard for bi-directional
communication over short distances. The Datrax uses this port to communicate with modems,
printers, laptop and personal computers. Often only three lines are required (Send,
Receive & Ground).
Call Brent
Hazelwood for a free evaluation of your requirements (888) 683-9871.
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