Monitoring the degradation of the antioxidant in transformer insulating oil can result in substantial savings by extending the service life of the oil and by slowing down the transformer aging process. Common inhibitors that prevent oxidation of the electrical insulating oil in transformers include 2,6 ditertiary-bytyl paracresol (DBPC) and 2,6-di-tert-Butyl Phenol (DBP). ASTM Method 2668 specifies measuring

DBPC and DBP concentrations by infrared analysis, which has typically been done using an FT-IR spectrometer. However, regular testing is typically not done as often as it should because of the time and expense to transport samples to a laboratory. Due to its complexity, cost and environmental requirements, an FT-IR spectrometer is usually impractical to move out of the laboratory into the field.

The InfraCal Filtometer from Wilks Enterprise, with a 2.7 micron filter specific for the OH absorbance band (common to DBPC and DBP) and a 0.2 mm pathlength sealed cell, can accurately measure the inhibitor on site from 5% down to 0.05% in less than one minute. It is an inexpensive, easy-to-use field analyzer. The InfraCal Filtometer enables more frequent testing of the antioxidant inhibitors and permits measurements to be made on-site with a substantial cost savings over laboratory analysis.

The InfraCal Filtometer is a fixed filter infrared analyzer that, unlike an FT-IR spectrometer, has no moving parts and an insignificant optical air path. This makes it portable, rugged and suitable for use in a field environment. An internal calibration table and easy-to-use operator interface allows for analysis by non technical personnel. DBPC and DBP have a characteristic infrared absorption band at 2.7 microns (3650 cm-1). As the inhibitor is depleted, the infrared absorbance decreases. An internal calibration table in the InfraCal Filtometer allows for a digital readout in % DBPC or DBP.