The Azbil KFDB is a field-mounted pneumatic differential pressure controller — a technology that has persisted in process industries because it needs no electricity to function. A differential pressure element (diaphragm or bellows, depending on the range) converts the process DP into mechanical displacement via a torque tube. This displacement drives both the local indicator — a 150 mm scale with red process-variable and green setpoint pointers — and a pneumatic flapper-nozzle transmitter that outputs a proportional 20–100 kPa air signal. The entire control loop runs on compressed air: the supply input at 140 kPa powers both the measurement and the output stages.

What control actions can the KFDB execute?

The KFDB supports the full complement of pneumatic control actions: proportional-only with manual reset, PI, PID, PD with manual reset, ON/OFF, and differential gap. The proportional band is adjustable from 5 to 500% in direct or reverse action. Integral and derivative times each range from 0.05 to 30 minutes. These functions are implemented on a modular pneumatic circuit board — individual control units can be added or removed to change the control law without replacing the entire instrument. A local setpoint knob on the front panel or an internal adjustment provides the target value, with an optional remote pneumatic setpoint input.

Where does the KFDB fit in a modern plant that is mostly electronic?

Pneumatic controllers remain specified for hazardous areas where intrinsic safety is simpler with air than with electronics — no ATEX barriers, no galvanic isolators, no certification paperwork for the instrument itself. The KFDB's IP54 / NEMA 3 enclosure and -30 to +80 °C operating range make it viable outdoors and in unconditioned plant environments. The 20–100 kPa output can drive a pneumatic control valve directly, or be converted to 4–20 mA via an I/P transducer for integration with a DCS. The twin-bellows detector and damped spiral elements provide inherent resistance to process pulsation without narrow constrictions that could clog in dirty service.