Use of a photoionization detector may be more appropriate. In drying ovens or unusually hot locations, solvent vapors with high boiling points may condense in the sampling lines and produce erroneous (low) readings. Meters typically have interchangeable probes for measuring electric and magnetic fields. The chamber is deployed directly in the area to be measured. Interference from other gases can be a problem. Some interfering compounds can result in false positive readings. In other cases, the sensor can be damaged, or «poisoned» by exposure to certain compounds, in which case it will need to be returned to the CTC for sensor replacement.
The response factor is the ratio of the detector response for a particular chemical relative to a reference gas, usually isobutylene. Annual calibration is handled through the CTC. Maintenance Reagent-grade isopropyl alcohol for use in these types of instruments can be obtained from the CTC AESP. Isopropyl alcohol must be added to the unit after five to six hours of operation under normal conditions. Wipes and Sponges Wipes and sponges are often used because they can sample larger surface areas and have a higher collection efficiency compared to swabs. They can also be used in a dry or wet fashion.
Smoke released inside an enclosing hood, such as a laboratory fume hood or spray booth, or outside an exterior hood, such as a snorkel, slot ventilation, canopy hood, downdraft table, or side draft hood, will help visualize whether contaminants will be effectively contained and/or captured. Maintenance When the photodetector is not being operated, it should be placed in its plastic bag, which should then be closed. They are valuable when evaluating laboratory hoods for adequate face velocity. Refer to the CTC ALEP for specific information, or to the SLTC. Instrument Use Physical Measurements Type of Instrument Measured Substance Application Stop time meter Time Calibration Tachometers Mechanical speed Flywheels, belts, cylinders, lathes, etc.