Abstract: A photometric analyzer for measuring differential total reduced sulfur in a sample gas stream is provided. It includes a supply for a sulfur bearing gas sample, an oven having an inlet connected to the supply for converting TRS to SO.sub.2 and an outlet through which the gas sample is discharged. A valve is connected to the outlet of the oven. An SO.sub.2 bypass line is connected between the supply and the valve. A sample cell with transparent ends has an inlet adjacent one end connected to the valve for alternately receiving sample gas from either the oven or the bypass line and has an outlet adjacent the other end. A pump connected to the sample cell outlet draws the gas sample through the sample cell. A light source at the one end of the sample cell directs light of a predetermined wave length through the sample cell. A light sensing device at the other end detects the amount of light passing through the sample cell at any given time and provides an output signal to an analyzer.

Abstract: The present invention relates to an apparatus which can be inserted between the stack and a transceiver of a transmissometer to provide zero and span measurements using the primary light source from the transceiver. The apparatus includes a calibration device mounted between the transceiver and one side of the stack and within the path of the light beam. A zero reflector is mounted within the calibration device for movement back and forth between an inactive position and an active position within the path of the light beam to reflect the same amount of light back into the transceiver as the retro-reflector would across the stack when the stack is clear of smoke. In addition, means is connected to the zero reflector for accomplishing this movement. A span filter is also provided within the calibration device which is movable between an active position in the light beam path to provide an upscale reference calibration check.

Abstract: A dilution extractive probe assembly for sampling a gas stream in a stack is provided. It includes a hollow tubular dilution probe having a first end for receiving a sample of the gas stream from the stack to be analyzed and a second end through which the sample is discharged after dilution. A first filter is provided at the first end of the probe for filtering the sample gas it passes into the probe. A critical orifice is located within the probe downstream of the first filter. A first heater is provided for heating the first filter to maintain the sample at a temperature above the dew point of the sample gas. A partial vacuum is created for drawing the sample through the filter and into the probe. An eductor is located adjacent the second end of the probe for mixing the sample with a dilution gas. A second heater for heating the eductor to maintain the sample gas at a temperature above its dew point as it passes through the eductor is provided.