Decoder System Design

Overview of Decoder Operation

Decoder in Valve Box

Two-wire decoder technology permits control of large irrigation systems, over relatively long distances, by inserting waterproof decoder modules as needed in a low voltage, direct burial two-wire path. The wire is cut wherever station control is needed, and the decoder wires are spliced into the path. The decoders are then connected to local standard 24 VAC solenoids for individual operation of valves and similar devices. Each decoder is uniquely addressed, and both the signal for their address, and the power required for solenoid operation, are sent over the single pair of wires. Up to 99 decoders can be individually operated over a single pair of wires in this manner.

Decoder Benefits

  • Decoder systems save wire. The greatest attraction to many users is the ability to operate 99 stations with only two wires (usually 14 AWG/2.08 mm2 solid copper), instead of 100+ wires. They can also save connectors and labor associated with large numbers of individual wire runs.
  • Decoder systems are electrically efficient. They have the ability to operate large numbers of solenoids over relatively long distances. 
    • With 14 AWG/2.08 mm2 solid wire, a controller can activate solenoids up to 10,000 ft/3 km away (metric diameter based on commonly available wire sizes in international markets. IDWIRE1 is technically 1.63 mm diameter, or 2.08 mm2 area).
    • With 12 AWG/3.3 mm2 dia. wire, they can operate up to 15,000 ft/4.5 km. Longer runs are possible with even heavier wire, but not practical.
    • The ACC family of decoder controllers provides up to 6 two-wire paths to the field. Therefore, a controller can operate up to 15,000 ft/4.5 km in each of 6 different directions.
  • Decoder systems are lightning resistant. While no irrigation system is immune to lightning, decoder systems have less wire in the ground and, when properly installed, have excellent grounding and surge suppression. They are popular in regions with high lightning exposure.
  • Decoder systems are relatively easy to troubleshoot. There are only two wires per path, and a single output module for the decoder functions, equipped with diagnostic LEDs. The controller operating system is the same as a conventional ACC, and for customers who are already familiar with ACC operations there is little new to master in decoder programming.

Typcail Field Decoder Wiring

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