The on-board microprocessor and non-volatile memory store all calibration factors and directly control a proportioning electromagnetic valve.

The digital interface operates via RS-485 (optional RS-232), and provides access to applicable internal data, including FLOW SET POINT, ACTUAL FLOW, ZERO ADJUSTMENTS, and LINEARIZATION TABLE ADJUSTMENTS.

A "Smart" Digital Mass Flow Controller automatically nulls (AUTO ZERO) the sensor zero offset whenever the flow set point is below 2% of full scale. To accommodate this feature, the control valve must fully close under that condition.

Provisions are made to either disable, force, or store the current auto zero via digital commands.

The firmware for the DFC provides functions to register total gas quantity (Totalizer). The total mass of gas is calculated by integrating the actual gas flow rate with respect to time.

Digital interface commands are provided to:

• Set the Totalizer to ZERO.
• START/STOP totalizing the flow.
• READ the totalizer.
• START the totalizer at a preset flow.
• STOP the flow at a preset total.

Multi-Gas Calibration: the DFC is capable of storing primary calibration data for up to 10 gases. This feature permits the same DFC to be calibrated for multiple gases, while maintaining the rated accuracy on each individual calibration.

Conversion Factors: conversion factors for up to 256 gases are stored in the memory of the DFC. Conversion factors may be applied to any of the ten gas calibrations via digital interface commands.

Flow Alarms: High and Low gas flow ALARM limits are programmed using the digital interface. Alarm conditions are reported via the digital interface or can activate the contact closure options.

Programmable Flow: Free Aalborg® software is included to support programmable flow modes, allowing execution of custom programming of up to ten steps. Various flow configurations include ramping, linearized increasing and decreasing modes.

The AUTO TUNE function allows the DFC to automatically optimize control response for the gas under actual process conditions, During the AUTO TUNE process, the instrument adjusts PID gains for optimum step response, and determine key control valve characteristics (only available on units with less than 80 L/min maximum flow).

Contact Closure: two sets of dry contact relay outputs are provided to actuate user supplied equipment. These are programmable via the digital interface, such that the relays can be made to switch when a specified event occurs (e.g. when a low or high flow alarm limit is exceeded or when the totalizer reaches a specified value).

Valve Override: means are provided to force the control valve fully open (purge), or fully closed via either the analog or digital interfaces.

Self-Diagnostics: whenever power is first applied, the DFC runs a series of self-diagnostic tests to ensure that it is in optimum working condition.

The flow set point, measured gas flow, and associated totalizer data is scaled directly in engineering units via digital interface commands.

The following units of measure are supported: % of FS, mL/min, mL/hr, scfm, scfh, sL/min, sL/hr, lbs/hr, lbs/min, and one user defined unit of measure.

Leak Integrity: 1 x 10-9 smL/sec of Helium maximum to the outside environment.

Balanced Power Supply: the DFC operates on ±15Vdc. The current requirements for the positive and negative power supplies are balanced such that the current in the power supply common connection is minimized. Maximum power consumption is 13.5 watts at ±15Vdc.