Shipboard Technical Support (STS) at Scripps Institution of Oceanography and the earlier groups which evolved into STS have operated a high-precision temperature calibration facility at SIO for half a century. Initially the facility was focused on the calibration of Deep-Sea Reversing Thermometers (DSRTs), but shifted emphasis in the last 25 years with the increased use of electronic instrumentation (CTDs). In addition to calibration of sensors and instruments within the department's inventory, we offer services to scientific groups at SIO and the oceanographic community at large. In recent years we have received instruments from across the US, Germany, the United Kingdom, Norway and Russia. Over the years, STS staff have worked with engineers from CTD manufacturers (i.e. Neil Brown, Falmouth Scientific and Sea-Bird Electronics) in developing our calibration procedures. The investment in equipment and personnel training was an operational necessity long before commercial CTD vendors began to offer this service, and as discussed below high-quality in-house calibration remains a necessity for the department.

The STS standard practice for calibration of a pressure or temperature sensor is to provide a complete record of every data point taken, including those that might not be used in calculating coefficients. This is the only way that one can really understand how a sensor is responding. Reports from commercial vendors sometimes include only the coefficients, or at best the data taken when the instrument is at complete equilibrium. This does not give an accurate picture of true sensor performance. During a cruise it is impractical to wait an hour at each isotherm for the instrument to equilibrate before recording data. In the STS Calibration Laboratory we typically record data taken soon after a temperature or pressure change, and follow the sensor until total equilibrium is reached. It is enlightening to see how sensors perform during simulation of real world conditions. 

The Ruska Deadweight Tester owned by STS had been in use since before 1998. It is very labor intensive to operate and maintain in calibration; modern versions have many automated features. Current budget restrictions have resulted in a downsizing of the staff trained to use the Calibration Laboratory. Upgrading the Deadweight Tester will permit the existing staff to keep up with the demand for pressure calibrations, both from within STS and from outside scientific groups.

A Fluke model P3125-BAR dual piston tester was been selected as best fitting our requirements. This model permits calibration to full ocean depth (1 to 1100 bar), with an accuracy of 0.015% of reading. The Fluke P3000 series incorporates over 50 years of experience in the design and production of primary pressure standards. The piston/cylinder assembly is manufactured from materials proven to provide stability, durability and low thermal expansion and distortion. The Fluke Deadweight Tester is accompanied with accredited calibration reports (ISO/IEC 17025) and will be trimmed to local gravity upon order.

The Fluke instrument was purchased with funds from this award and is in service.

Please report errors in award information by writing to: awardsearch@nsf.gov.