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Overview
Remote monitoring of process plant is an established technology
which uses transducers and contacts to measure physical parameters
and equipment status. The resultant signals are converted
into data streams which are sent over a communications network
to a Central Station and then displayed in graphical format
on a monitor for the operator.
Unfortunately, there are a number of parameters which cannot
be converted into electrical signals and the operator at the
Central Station is often faced with making critical decisions
based on incomplete information.
Recent changes in video signal coding and data transmission
have allowed live video pictures to be transmitted concurrently
with data streams over low speed communications links, allowing
the operator at the Central Station to see live video pictures
of the remote site together with the data displayed as real
time active graphics. Using this technology, the Sitewatch
video system allows the operator at the central location to
view live video pictures and alarm status from up to 16 locations
simultaneously and establish a voice link through the system
with personnel at a remote site.
Video and data can be transmitted via the Public Switched
Telephone Network (PSTN), over dedicated lines, microwave
and radio links and via company networks and Intranets.
Applications
Applications for remote monitoring with Video include:
- Validating intruder and fire alarms before calling the
emergency services. Identifying personnel and determining
the extent of damage and appropriate response.
- Checking that the site is in a safe condition before
remotely starting or changing settings of plant or equipment.
- Confirming the "rate of change" of a parameter that has
caused an alert e.g. when a flood level alert has been received
at the Central Station is it useful to be able to "see"
the rate at which water is flowing and rising or falling.
- Monitoring the effect of control action on processes
with long response times e.g. changing the setting on a
lock weir gate.
- Monitoring maintenance tasks and personnel working un-accompanied
at a remote site. · Monitoring the status and performance
of legacy equipment by focusing the video camera on a Mimic
panel at the remote site.
Typical Installation Requirement
Colour or black and white Close Circuit Television (CCTV)
cameras are mounted at strategic locations at the remote site
and connected to a Video Terminal Unit (VTU). The VTU combines
the function of a CCTV camera interface and telemetry Remote
Terminal Unit (RTU). The cameras can be equipped with motorised
Pan, Tilt and Zoom (PTZ) controls, which are operated from
the Central Station. The VTU interfaces to the remote site
equipment using digital, pulse and analogue inputs and provides
control facilities using digital and analogue outputs. Digital
outputs are used to operate process controls and switch on
lights in an otherwise dark building when the video link is
established.
The CCTV camera pictures are viewed at the Central Station
using a Personal Computer (PC) or Workstation running the
Lee-Dickens' Sitewatch Telemetry or Supervisory Control and
Data Acquisition (SCADA) software. The operator can view one
or more of the video pictures in pop-up windows on the Central
Station monitor. The video data can be viewed in real time
and recorded on the Central Station disc for archiving and
replay.
Network connected systems
Sitewatch Central Stations can be connected to RTUs and
PLCs via an Ethernet Local Area Network (LAN), sharing an
existing IT network with other services and applications where
necessary. Ethernet LANs operate at 10Mbs or 100Mbs and generally
have lots of spare capacity. The video server has a direct
Ethernet connection and can be supplied to operate with up
to 4 cameras per video server - a number of video servers
can be connected onto the network. Picture update is generally
in real time but is dependent on network capacity. Additional
Sitewatch Central Station client computers can also be connected
onto the Ethernet LAN.
Dedicated Line systems
The Central Stations, RTUs and Video Terminal Units (VTUs)
are interconnected via dedicated copper or Fibre Optic lines
using modems typically operating at 33Kbs or 56 Kbs. The VTU
is a wall or 19" rack-mounting device which has a 32 bit processor,
digital and analogue inputs and outputs and 4 CCTV camera
connections. Picture update rates are limited by the speed
of the modem link, but with 4 cameras selected it generally
takes 6 seconds to scan through 4 pictures and the update
rate per picture when selected is 1 to 3 frames per second.
PSTN systems
The Central Station, RTUs and VTU are interconnected by the
PSTN using 56Kbs modems. The RTUs and VTUs operate as dedicated
line systems when connected via the PSTN. Video from 1 to
4 cameras at the same site can be displayed on the Central
Station at any one time. The RTUs and VTU also log data at
the remote site and upload the data to the Central Station
when a connection is made between the Central Station and
RTU.
Technical Details
The Central Station operator can configure the monitor display,
activate recording, establish audio links and control the
Pan, Tilt, Zoom (PTZ) and focus of the cameras at the remote
sites using the PC keyboard, mouse, tracker-ball or touch
screen.
Video streams can be viewed at selected speeds of up to
30 frames per second, depending on the bandwidth of the communications
network and the number of active cameras selected. Video compression
is fully compatible with the ITU-T standard H.320/H.323.
The Central Station database is accessible by several client
PC's simultaneously, which can be connected locally or remotely.
Recording tasks can be initiated manually or automatically
by configuring a built in profile editor. A ring buffer recorder
is available to store pre-alarm or incident video streams.
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