Device integrates gas flow control functions with mass flowmeter

Simplifies basic flow control installations and helps network multiple instruments.


The Compod from Sierra Instruments serves as a programmable control module working with mass flow meters to create gas flow control systems.

The company says that with its advanced capabilities, coupling the Compod with Smart-Trak mass flowmeters and controllers greatly simplifies basic flow control installations and permits networking of multiple instruments using open-source Modbus RTU protocol. With two digital outputs and one analog input, the Compod can be configured by the end user for a wide variety of process controls including:

  • Gas mixing and blending;

  • Gas ratio control;

  • Simple batch processes;

  • Triggering alarms;

  • Starting or stopping gas flows automatically under user-defined conditions; and

  • Gas flow totalization.

Compod also monitors the functionality of the mass flowmeter or controller and includes diagnostics, notifying users of faults or system updates.

The Compod mounts to any Sierra Smart-Trak 100 Series unit, converting the instrument’s internal RS-232 communications into multi-drop RS-485/Modbus RTU. With Modbus, multiple instruments can be daisy-chained over a single network. When used with a PLC or master computer, each instrument equipped with Compod becomes a node capable of sending and receiving data and commands.

Users can use Sierra’s provided software or write proprietary software using open-source Modbus protocol to configure standard functions for the Smart-Trak 100 Series. Compod’s two digital input/output channels and the analog input channel and a configurable pulse output channel can automate gas processes without the need for an external PLC or computer.

—Edited by Peter Welander, process industries editor,
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