Model 106-L Ozone Monitor Manual Rev. E
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up, fluctuations in photodiode voltage should be limited primarily to the last digit
displayed. The lamp test also calculates an electronic offset and standard
deviation of the measurement itself, displayed in the above example as 1.2 ppb
for the electronic offset and +/-1.85 for the standard deviation. The standard
deviation is a quantitative measure of the lamp and associated electronic noise.
Electronic offsets should normally be -5 to 5 ppb equivalent. After running the
lamp test for a few minutes, values above 2.50 for the standard deviation
usually indicate an excessively noisy lamp. Lamps seldom “burn out” but may
become noisy with time and need to be replaced. Some lamps become noisy
after only a short period, while others will be extremely stable for years. If your
lamp fails the lamp test during the first year of operation, contact us for a new
lamp under the instrument warranty. Contamination of the detection cell may
also cause a high standard deviation, in which case the flow path should be
cleaned with methanol and the internal ozone scrubber replaced. Please
contact us for detailed procedures if you want to perform these operations on
site.
