Raw TPC temperature data were converted to thermistor resistance (R, ohms) using a fourth-order polynomial equation fit with empirically derived calibration coefficients:
Temperature (K) was calculated from thermistor resistance using the Steinhart and Hart relationship (Anonymous, 1980):
The manufacturer-supplied coefficients for the thermistor used for all the tool runs at Site 1226 (serial number 0047-25) are
TPC pressure in psig was computed from raw bit count data using an empirically derived constant = 0.1785 psi/bit. Because local hydrographic profiles were not obtained, depth (meters below sea level [mbsl]) was computed from measured pressure (psig), assuming an average seawater density of 1.025 g/cm3.
Output from the conductivity sensor was digitized by the 12-bit Maxim MAX147 A/D converter, and values were recorded as raw bit counts. Because the conductivity circuit was designed to avoid polarization and electrode corrosion in seawater, measured values oscillate rapidly between two extreme values. A change in the difference between the minimum and maximum values indicates a change in the conductivity of the medium contacting the electrodes. Conductivity data for each sensor were normalized by subtracting the mean value from each data point and then taking the absolute value. These normalized conductivity values, expressed in bits, should not be confused with standard seawater conductivity measurements. Large values of normalized conductivity correspond to a gas headspace and small values correspond to the presence of seawater at the sensor electrodes. This is the opposite of what would be expected and is simply an artifact of the sensor electronics. Visual calibration of the conductivity signal was accomplished during a Monterey Bay Aquarium Research Institute remotely operated vehicle dive in October 2000 using an actual TPC tool assembly.