Intelligent microprocessor based devices, for monitoring and controlling
equipment at remote sites, have been introduced by Lee-Dickens. The
Sitewatch MIDI 8 Remote Terminal Unit (RTU) represents the next-generation
of class-leading RTU's used primarily as part of a supervisory control and
data acquisition system (SCADA) or a telemetry system, says the company.
The MIDI 8 uses the same distinctive IP65 rated moulded enclosure as the
previous model, but the use of the latest compact surface-mount technology
and RoSH components has freed up space for a number of additional features.
These features include a broad range of interchangeable networking
communication options including PSTN (fixed line modem), GSM and LAN
Ethernet communications. The unit also has a transient to transmitter logic
(TTL) interface that enables off the shelf modems to be used. This means a
GSM or Ethernet modem can be easily swapped should it fail or the
communications method need to be changed. The modems and radio transceivers
are powered from the RTU itself and supported by standby batteries should
mains power fail.
As well as increased networking options, additional I/O has been added. The
Sitewatch MIDI 8 has 8 optically isolated digital inputs, 8 differentially
selected analogue inputs and a further 3 digital outputs fitted as standard.
The digital input capacity can be increased to 16 or 4 pulse inputs can be
added by fitting a small expansion board. Digital and analogue inputs are
configured by on-board links to provide a two wire interconnection to site
equipment. A 24VDC 250mA supply is available to power external analogue
transducers.
Each Sitewatch MIDI 8 has two serial data ports, one of which is configured
for the Master Station communications interface and a second that can be
used for local interrogation, connection to other RTU's via a Local Area
Network or for interfacing to other intelligent site equipment.
All field connections are made to plug-in screw terminals on the
input/output board. A four line by 20 character LCD and 16 key keypad can be
fitted for local operator display and interrogation. The channel names to be
displayed in the RTU can be specified by the user and can therefore be in
any language to suit the operator.
The Sitewatch MIDI 8 has a built in data logging facility for all inputs and
outputs and a real-time clock used to time and date stamp the logs. The
baseline operational software (boot software) is held in non-volatile EPROM
memory with application programs and critical site configuration data held
in Flash ROM. Logged data is held in battery backed CMOS static RAM, says
the company.
