Instrumentation: transmitters and controllers on the canvas

Field instruments are first-class wireable nodes here, not annotations. A flow transmitter and a pressure transmitter sit in the line, pass their stream through completely unchanged, and report their reading on a signal wire — a distinct edge kind that carries information rather than material — to a controller. In this let-down station the FT reads the 200 mol/s flowing through it and the PT reads the 20 bar downstream of the control valve. Each controller compares its reading against a setpoint and reports the measurement, the setpoint and its output. These two controllers are report-only, deliberately. Neither has an OUTPUT wire, so nothing is written back and the flowsheet solves once — this is the instrumentation and measurement layer on its own. Give a controller an output wire plus an output_param and the same machinery becomes a genuine closed loop: the output is written into the manipulated variable and the flowsheet re-converged through a Wegstein outer loop. Bounded: a signal edge never carries material, so it can never affect a mass or energy balance — which is exactly why a transmitter is safe to insert anywhere in a working flowsheet. The steady-state controller is proportional by default and therefore keeps a genuine offset (it converges the self-consistent operating point, not the setpoint); integral removes that offset. Derivative action needs a time history a single steady-state solve does not have.