Weathermatic SLFSI-T10 Design Manual

Two-Wire System Design Guide
Welcome to the Weathermatic Two-Wire System Design Guide. This guide has been developed
to provide an overview and detailed notes and tips for contractors and specifiers who are working with
Weathermatic Two-Wire systems.
This guide includes the information necessary to specify a Weathermatic Two-Wire systems. Written
specifications in CSI and Microsoft Word format as well as CAD details reference herein are available on
the Weathermatic website at www.weathermatic.com
INTRODUCTION
Two-wire decoder technology has been around the irrigation industry for more than three decades
beginning in the golf industry (primarily in Europe) in the mid 1980's as a cost effective method for
wiring irrigation valve-in-head rotors used extensively in golf irrigation systems. The cost savings was a
result of eliminating thousands of feet of copper wire used to control valves. Two-wire systems also
made it far easier to trace and connect wire from the irrigation controller to the sprinkler head without
having to use specialized tone equipment and multiple installers.
By the late 1990's, manufacturers began to bring two-wire technology to the U.S. Early systems
primarily used DC current, which is highly susceptible to faults in wiring, which led to a number of
system failures as contractors had to learn to be diligent with wiring. Additionally, DC latching solenoids,
which are highly susceptible to "sticking" open, were required to be used on each irrigation valve.
Fortunately, irrigation manufacturers figured out how to convert the two-wire DC signal to AC thus
eliminating the valve failure problem.
Today, two-wire irrigation system are a high majority of the types of new irrigation systems being
installed in the U.S. especially in the Central and Eastern U.S.
WHAT IS A TWO-WIRE IRRIGATION SYSTEM?
In a two-wire decoder system, a single pair (thus the name "two-wire") of poly insulated wires is run to
all valve locations on a "wire path". At each irrigation valve location, a valve "decoder" is wired to each
valve. Each decoder has a programmable address (typically the zone number), which identifies it to the
two-wire decoder irrigation controller. The two-wire cable is connected to all these decoders on the
wire path.
During operation, the controller broadcasts an "ON" command to activate a specific address. All of the
decoders wired on the same two-wire path "decode" the message, but only the appropriate decoder
responds and turns the attached valve on. The decoder also reports back to the controller that it
received the command and has responded. The lack of response or an electrical issue will trigger an
error code on the controller to aid in troubleshooting. When the irrigation cycle is finished, the
controller stops sending the "ON" command and decoder responds by turning the valve off.
Electrically a two-wire controller actually sends the "ON" command hundreds of times per second thus
enabling the system to communicate to multiple decoders at the same time over the same wire path
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