The probe has automatic temperature compensation for temperature-corrected buffer values. A calibration sleeve is used to calibrate DO in the wastewater laboratory before each sample event. The instrument automatically measures and compensates for temperature and total atmospheric pressure. The Orion Model 840 DO meter and the Orion Model 140 conductivity meter are used as backups if a problem with the main meters occurs in the field. USGS midsection methods, as described in the Water Measurement Manual, are followed.
Calibration is performed at the factory.
The amount of acid necessary to bring the sample pH down to 4.5 is proportional to the total alkalinity in the sample. The volume of acid required to change the color of the sample reflects the ammonia concentration of the sample. A small amount of dye is added to the sample, and buffer solution is added until the pH of the sample reaches 10. If calcium and magnesium are present in the sample, the sample turns red. The amount of EDTA required to turn the sample blue represents the hardness of the sample.