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STM-12B Mercury Sorbent Trap Monitoring System

STM-12B Mercury Sorbent Trap Monitoring System

The automated STM-12B MercSampler™ for Sorbent Trap Monitoring Systems is designed for continuous dual sampling of vapor-phase mercury emissions from stationary combustion sources, in accordance with the U.S. EPA MATS published in 40 CFR, Part 60-63, Appendix A, Subpart UUUUU and Performance Specification 12B.

The Apex Instruments STM-12B MercSampler™ simplifies most sampling requirements by automating data acquisition, sample flow adjustments, leak checks, calculations, temperature control, and calibrations. Data is easily transferred to a Microsoft Windows based PC through Ethernet, USB or an optional Wireless Interface. The STM-12B MercSampler™ captures all data necessary for paired sorbent trap sampling in accordance with PS 12B. The sample flow rate is controlled proportionally to the stack flow rate and determines the standardized volume extracted through each sorbent trap. To collect the samples, two diaphragm vacuum pumps which work with the proportional valves and mass flow sensors, pull the samples through sorbent traps.

All applicable components are rated 120V/60Hz or 240V/50Hz.

SKU: STM-12B Category:


Performance Specification 12B – Specifications and Test Procedures for Monitoring Total Vapor Phase Mercury Emissions from Stationary Sources Using a Sorbent Trap Monitoring System – EPA Literature PDF


Sampling unit:

  • Fully automated paired sampling
  • Proportional flow control
  • Customer configured alarms
  • Dual gas meters with optical encoders (1 cubic cm resolution)
  • External inputs: stack flow, remote pause, moisture analyzer

Stirling cooler:

  • Robust, closed, dual-channel gas conditioning system
  • Cools gas to constant dew point
  • Removes moisture and acid gases
  • Uses acid-scrubbing sorbent

Heated sample probe:

  • Dual-trap probe
  • Dual-zone heater
  • Insulated junction box
  • Stack, trap, and probe thermocouples
  • C276 alloy (Hastelloy)
  • Cam-lock port connecter

Heated umbilical/sample line:

  • Heavy-duty, lightweight
  • Self-regulated
  • Replaceable sample lines
  • Flexible, robust construction with high-temperature jacket


  • Powder-coated aluminum
  • Easy-access door
  • Durable compact design
  • Optional heating and cooling system
Condensation bottles that collect knockout moisture from the stack sample allow for accurate Method 4 to be performed without additional testing.


Designed with easy access to internal components for field service and maintenance.


  • Dry gas meters:
    • Model SK25EX series, positive displacement type
    • 0.7 liter per revolution
    • Optical encoder sensor with quadrature pulse output
    • 8-digit LCD display, 1 cubic cm resolution
  • Sample pumps:
    • BTC diaphragm, brushless motor – 12 VDC, 20 inHg vacuum, 10,000 hour MTBF, 3900 RPM, Max. PSIG 24″
  • Sample flow control:
    • Stainless steel sample manifolds fitted with mass flow sensors, vacuum sensors, and proportional valves
    • Proportional or constant flow sampling
    • Mass airflow: proportional flow control, 100 to 2000 ccm, port-style, manifold mount
    • Proportional valve: voltage-sensitive orifice (VSO), 12 VDC
  • Data acquisition control board (DAC):
    • Enhanced flash 16-bit RISC based microcontrollers; main and digital signal processing (DS), real-time clock with auto backup and write protection to external SRAM
    • High-speed 14-bit A/D converter with parallel DSP interface
    • SD memory card for data storage – stores up to 99 tests (30-day test runs), embedded ethernet port with full TCP/IP protocol and 256-bit encryption
    • USB 2.0 comm input connection
  • Thermocouple multiplexer:
    • Accepts type-K thermocouple inputs; input protection includes gas discharge tubes for ESD and surge protection
    • 11 pic microcontrollers, 1 for each channel and MUX circuitry
    • MUX circuitry to receive multiple inputs and transmit selected output
    • 10 microcontrollers, one for each optically-isolated channel
  • Integrated temperature control:
    • Designed into DAC for probe/trap heat control output via 25-amp solid-state relay
  • Barometric pressure:
    • 600 to 1100 mbar, 17.7 to 32.4 inHg, temperature compensated, amplified output
  • Vacuum:
    • 0 to 30 inHg, 0 to 101 kPa, 2% accuracy
  • Communications:
    • PC user interface via Ethernet
    • Remote access and control via an onboard configurable router to owner’s network computer
    • Optional TCP/IP MODBUS (ASCII or RTU) communications to the DAS
    • Optional interface to DAS system via TCP/IP Modbus


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