Problem
An oceanographic researcher wanted a small battery operated temperature measuring data logger that would operate at most ocean depths and at -50°C at the poles. The instrument must have a simple means for attaching it to a cable.
Solution
We designed the electronics around an off-the-shelf low power processor and memory module. This was mated to a circuit board produced by Alpha Omega that carried the analog to digital converter, power control, and communication circuit. This circuit board carried cradles for fastening batteries to the assembly.
The electronics were designed to operate over a temperature range of -50°C to +50°C operation, but finding a battery that delivered current at -50°C was a bit of a challenge. We used a DD size 30 Ampere hour lithium-oxyhalide battery that is rated for operation at extremely cold temperatures. The unit could also be operated on three ordinary alkaline C cells at warmer temperatures.
The unit was packaged in a machined Noryl plastic pressure case with the temperature probe recessed in one end to protect it during handling. The case had two shallow grooves that fit Delrin clamps that fastened around the case. These clamps could be locked around a cable to hold the unit in position. Other types of clamps could be produced to attach the case to different features.
Data was recovered by opening the case and connecting the unit to a standard serial port on a PC. We supplied a program to extract the data and save it in a common file format. Some versions contained an inductive communications circuit for use with the AO Inductive Communications Interface.
Results
The 9102 was used in a variety of applications. One of the most interesting was at the poles where strings of 9102s were lowered into the ocean through cracks in the ice to measure temperature differences at different depths. In this application the unit was subjected to a sudden approximately +50°C thermal shock as it left the atmosphere and plunged into the near freezing water.
