Technology for the higher dust loadings found after unabated combustion processes or after Electrostatic Precipitators

A light source (typically an LED) shines light through the particulate in a stack and the amount of transmitted light is measured by a receiver. In a single pass instrument the receiver is mounted on the opposite side of the stack while in a double pass instrument (UP EPA PS-1 compliant), the light is reflected back to the transceiver by a retro-reflector on the far side of the stack. There are two parameters that Opacity instruments may be designed to measure:

• First a measurement of the Stack Opacity (stack blackness) according to the simple equation:
  Opacity = 100 (1 – Received Light/ Transmitted Light) %
• Secondly, a measure of the stack extinction which has a linear relationship with dust concentration for a particular type of dust and dust size:
  Extinction = Natural Log (Received Light/ Transmitted Light)

• Compared to other Opacity systems, PCME’s PS-1 compliant instrument has lower long term zero drift, meaning that it can be used to monitor dust levels as low as 10mg/m³ in a 5m stack without suffering from zero drift which causes errors when calibrating an instrument.
• The Opacity and DynamicOpacity™ measurement algorithms can be combined in certain instruments to provide a more reliable solution for dust measurement than pure opacity system.

PCME’s Double Pass Opacity instruments are available with a range of quality assurance features as required by US EPA PS-1 standards:

• Automatic Opacity zero check which challenges the full operation of the transceiver by measuring the signal when a mirror is automatically inserted into the beam after the final lens.
• Automatic span checks, to check ability of the instrument to correctly measure attenuation caused by an optical filter inserted ahead of the zero mirror.
• Audit filters which may be manually inserted into instrument for zero and linearity checks.