Arc

Learn what Arc is, what it is for, where it runs, and when to use it.

Arc is the Synnax language for automations. An Arc automation reads channels, computes values, and writes channels. It runs on the Synnax Core or on a Driver, where the data arrives, so its timing does not depend on your computer or the network. You write Arc in the Console, as text or as a graph of blocks.

What Arc is for

• Test sequences -> Open and close valves in stages, and go to an abort stage on unsafe values.
• Bang-bang control -> Hold a value between a low and a high limit.
• Computed values -> Write averages, rates of change, and unit conversions to channels that Synnax stores.
• Alarms -> Set a status when a value goes out of limits.

Flows

A flow sends values from channels, through expressions, to a channel with ->. The flow runs each time one of its channels gets a new value, after each channel has its first value. This flow writes the average of two pressure sensors to a third channel:

(tank_pt_1 + tank_pt_2) / 2 -> tank_pt_avg

Sequences

A sequence runs its steps in order: writes, waits, and stages. A stage holds until one of its conditions is true, and => next moves the sequence on. When the last step finishes, the sequence stops, and start_cmd can start it again. This sequence runs each time start_cmd becomes 1:

import time

sequence press {
    stage pressurize {
        1 -> press_vlv_cmd
        tank_pt > 300 => next
    }
    0 -> press_vlv_cmd
    time.wait(duration=10s)
    stage vent {
        1 -> vent_vlv_cmd
        tank_pt < 5 => next
    }
    0 -> vent_vlv_cmd
}

start_cmd == 1 => press

See the execution model for how stages, conditions, and writes run.

Where an Arc automation runs

You choose where each automation runs in its Driver list:

• The Core -> The entry Node 1 (or the number of your Core) runs the automation inside the Core. It needs no Driver. When the automation has an error while it runs, the Core logs a warning and keeps it running.
• A Driver -> The entry Node 1 Embedded Driver is the Driver that runs with the Core. A standalone Driver shows with the name of its computer. A Driver runs the automation next to the hardware it connects to, and can run it on a real-time loop. When the automation has an error while it runs, the Driver stops it.

Text and graph editors

When you create an Arc automation, you choose its Editor mode. You cannot change it later.

• Text -> You write Arc code. Use it for sequences and for automations with many conditions.
• Graph -> You connect blocks for channels, comparisons, and statuses. Use it for simple automations, such as alarms.

Arc, calculated channels, or Python