Development of a cave auto-sampler

Abstract

Researchers at the University of Waikato visit caves on a periodic basis to collect samples of drip water, which over geological time frames form stalagmites and other formations. However, most caves are remotely located, which makes it an arduous task to reach the study site and is economically infeasible for frequent visits. This thesis presents the development of an autonomous cave autosampler deployable inside caves for extended periods to collect drip water and log the atmospheric conditions such as temperature, pressure, and carbon dioxide. The auto-sampler is developed from two various aspects. Firstly, the collection and storage mechanism. Secondly, control systems, power management, and data logging. The sample drip water is collected from a positioned funnel and stored in an airtight 20ml sample vial through a syringe needle; a new sample vial comes into position on a weekly basis. A carousel styled turntable is designed to store fifty 20 ml sample vials in the minimum possible size. The sample vial position on the turntable is controlled by a stepper motor to maintain precise position relative to the syringe needle. Acrylic is selected as the primary material to reduce weight. Temperature, pressure and carbon dioxide readings are logged during switching operations. The electronics on the auto-sampler are turned off in an idle state, and the Arduino microcontroller is put into sleep mode to minimize power consumption. The auto-sampler has been tested in lab conditions extensively for position control, power consumption and overall performance. During position control testing, the sample vials made it to the desired position relative to the syringe position on most of the cycles. There are few minor issue which a affects the consistency of the auto-samplers operation such as back play in the linear actuator and flexing of the turntable during piercing of the sample. Based on a 50 week deployment, the auto-sampler has an energy requirement of 113.6Ah.