Commercially available in-stack transmissometers for opacity measurements presently only have the capability of a one point dynamic upscale check or no dynamic upscale check during operation. Sin order to perform necessary multi-point audits or linearity checks, the instrument must be removed from service or manually fitted with an external audit device. This requires access to the instrument which is often located at elevated stack heights with limited access and safety provisions. Thus, routine audits that should be performed are often not performed, with the accompanying production of low quality data. Transmissive liquid crystal displays have been determined to have accepted long term stability, thermal stability, spectral characteristics, and uniformity for use as calibration audit devices. By designing the proper pattern and multiplexing, stepwise attenuation of light is possible for multipoint calibration of the transmissometer.Eastern Technical Associates (ETA) proposes to develop and field test on industrial stacks a retrofit dynamic audit/calibration device that will fit major commercial transmissometers. This device will be capable of remote activation to produce three upscale points for audit, calibration and diagnostic purposes. The increased ease and safety in performing these audits will result in an increase in high quality data from opacity monitors.
