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What is SensorLink?
SensorLink is a
product that simplifies the task of telemetering a single
4-20mA sensor from a remote location to your local plant
operations center. It is an electronic system that is
intended for applications where continuous operation is
required. It has a built in modem intended for use over
private wire or leased phone lines (dry, not dial up). It
also has accommodations for connecting radios, RS232 type
systems, and TTL type systems.
What are the
typical uses of SensorLink?
As
an example, imagine that you have a water tank 4 miles from
your pumping operation. In order to run the pumps in a
safe and efficient manner, you must telemeter the level sensor
signal from the tank to your pump station. The PLC system
at your plant has an extra analog input available. Put a
send unit at the tank, a receive unit at the water station, and
power up. Your Sensor signal is updated four times a
second to your pump control system. 12 bit resolution
means that your signal will be reproduced at the receiver very
accurately. The send unit connects to sensors in three
ways: Loop powered, self powered, and 3 wire
powered.
Why would I want
to use SensorLink in my plant?
Why
else? Save MONEY. The normal solution is to install a
full PLC system at your tank location, and communicate with
your PLC at the pumping station. You will need a PLC
chassis, processor card, communications card, analog input
card, battery backed power supply module, modem (that operates
off of DC from the batteries), lightning protection for all
pairs, and an enclosure to put it in. Once you have all
of these goods, your production staff must assemble and test
the system, and your
engineering staff must program it. By the time the
electrical contractor is finished, you are facing well in
excess of $10,000. All of the features listed above are
incorporated into the SensorLink system, baring mounting it to
the wall and connecting three pairs of wire, simplifying your
task to a two hour job. And the cost starts as low as
$1398.00 per pair. That is 14% of the cost of the other
solution, in the conservative analysis!
The last system
I had installed was nothing but trouble!
The designers of SensorLink feel your pain. The most
common features for a remote location have been incorporated
into the base system. A battery charger / switch over
system is built into every unit. Add two batteries in
series for 24VDC, and the system will care for the battery
state. Worried about loss of communications? A
communications time-out feature in the receiving unit monitors
the health of the connection, and when trouble is sensed, a
form C relay is energized. You can use this indication to
tell your plant control PLC program to take precautions, such
as shutting down pumps or activating your plant alarm
system. You no longer have to dread learning of a
telemetry failure because the tank overflowed. And when
there are no troubles with your system, both the send and
receive units have a bright red display to help track sensor
performance at a glance.
Hey, I need a
system that can survive a severe environment.
Rest assured that this system has been designed to survive well
in a field setting. The enclosure is rated for IP54, and
the circuitry is designed to ride through your worst spring
lightning storm.
My last system
was destroyed by lightning twice a year!
SensorLink is designed with surge protection in the analog
input, analog output, AC supply input, and twisted pair
interface. Chances are that the cause of your past
troubles have been addressed in this product.
What kind of
special wire does this thing take?
The system is designed with an FSK modem inside of it that
sends signals over a standard twisted pair. The phone
company supplies a phone line service that is leased per pair
per mile per month. Historically, the leased line system
has an astronomically high up time, providing unprecedented
continuous service. In the case where you are running the
system inside of your own compound, simply pull a standard
100-120 ohm twisted pair and you are in operation. The
instruction manual
includes example wire types.
Phone lines are
quite inconvenient for my installation.
The SensorLink product is designed with a number of ways to
interface to a different method of communications. A pair
of external radios can be attached, as the system has
connections to the modem audio signals (for plain old radios)
or connections for an RS232 device (for smart data
radios). A variable DC supply is provided that can be set
to match the voltage on your radios. As each radio system
is different, consult our engineers for assistance. Since
audio, RS232, and TTL signals are
provided, just about any one of your favorite line driver,
fiber optic, radio or other device can be used to complete the
link.
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