In-rack liquid and gas flow computers

07 July 2008

ProSoft Technology’s line of single-slot in-PLC chassis flow computers are the only full-function in-rack flow computers on the market, and are significantly less expensive than stand-alone options.

The modules act as an add-on calculator using AGA and API calculation standards, without burdening the PLC with complicated flow algorithms.

There are versions for both Schneider Electric and Rockwell Automation PLCs. The new version 2.05 modules for Rockwell PLCs provide the following enhancements:

Modbus Dictionary: The flow computers provide a Modbus Master port to allow users to poll data from a remote chromatograph device. The modules have a vast internal Modbus map, so for the convenience of the user the upgrade was equipped with a Modbus Dictionary, which acts as an index for users to locate needed data.

Multi-Meter Runs: Stand-alone flow computers are often limited to a few meter runs, which increases implementation and maintenance costs, and creates more potential points of failure by complicating wiring designs. Alternatively, the inRAx supports anywhere from 8 to 16 meter runs, and now supports multiple streams (up to 4 per meter), and allows the PLC to switch the active stream via the module over the backplane of the controller.

Data Archival/Event Logging: Version 2.05 modules have an expanded data archival and event logging feature, which allows 35 regular daily and 48 regular hourly archives, and 1,440 daily and hourly extended archives per meter.


The in-rack flow computer version PTQ-AFC for Schneider Electric’s Quantum platform (shown in the photo) is now certified for custody transfer in Canada due to its accuracy in calculations and measures.

The module, which complies with AGA 3, 7, 8 and API 2540 measurement standards, operates with a precision keen enough to use when establishing prices for the gas being measured. Additionally, the PTQ-AFC module supports 16 meter runs, another means for better facilitating custody transfer of products between two parties and line balance for pipeline leak detection.

The PTQ-AFC module allows integrated process control and flow computer capabilities in a single-slot, in-rack solution. The module is equipped with three built-in Modbus ports which provide users with on-line meter configuration access for the defined meter data table. One Modbus port can be configured as a Master, providing a Modbus interface to gas chromatographs (for gas analysis) or to any other Modbus Slave devices. This level of flexibility in communication between the flow computer and Modbus devices is critical for pump stations and process plants.

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