​The ML®670 or 670 ®Open Architecture (OA) is a pre-engineered Continuous Emissions Monitoring System (CEMS) designed for use in EPA 40 CFR Part 60 and Part 63 compliance applications and for process control. This dilution based system can be configured to accurately measure Total Reduced Sulphur (TRS) with SO2​ and O2 on a dry basis. Additional gasses such as NOx, CO, CO2 can also be measured.

Both configurations of the ML®670 CEMS consist of a heated probe, heated sample umbilical, single bay cabinet, analyzers, control equipment, and a dilution air cleanup package. The Open Architecture version has the dilution air cleanup package mounted on a wall instead of the cabinet.

In order to measure TRS, sample is extracted from the process, filtered and dried, and then diluted with air. Using dilution extractive principles, pressurized dilution-air is used as the motive force to provide suction that mixes a small amount of stack gas into the same dilution air stream. The diluted sample is split between two streams. The main part of the sample is routed to a sample manifold so gasses such as NOx and SO2 can be measured. The TRS sample is scrubbed of any SO2 and then heated to oxidize the TRS compounds into SO2. The resultant SO2 measurement is then equal to the TRS concentration. An O2 sensor is located after the moisture removal, but prior to dilution in a separate stream, to provide a corresponding diluent measurement. A precision mass flow meter is used to determine an accurate, real time dilution ratio.

A programmable logic controller (PLC) performs all automatic sequencing of the sample cycle, daily calibration cycle, and back purge cycle. During calibration mode, zero and span gases are injected into the probe head to comply with EPA calibration requirements. Back purge air is delivered to the probe on a periodic basis to clean the heated probe filter, providing months of continued operation without maintenance.

In addition, the PLC has the ability to log fuel flows and provide the required analog outputs in units of diluent corrected ppm concentration (ppmc), lb/mmBtu, and lb/hour. Standard relay outputs that signal system status and fault information are also generated from the PLC. A RegPerfect® Data Acquisition System (DAS) may be attached to the PLC via Ethernet to provide long term data collection, compliance report generation, remote control and diagnostic information.​

The ML®670 is a self-contained system requiring single point attachment for power, instrument air, and calibration gases. All utility distributions are routed through the ML®670 internally. No duplication of utilities is required on the stack.​​