Thermistors – Deep-Well Geothermal Applications

Challenge

A customer developing groundwater-based geothermal systems required a highly accurate thermistor sensor capable of continuous submersion in potable water wells up to 500 feet deep. Each well would include two sensors, exposed to temperatures ranging from 40 °F to 70 °F.
The sensors needed to deliver ±0.5 °C or better accuracy, maintain long-term electrical integrity under moisture exposure, and feature robust 20 AWG leadwires with color coded jackets for easy identification.

Solution

UE’s engineering team recommended a 10 kΩ thermistor assembly soldered to a two-conductor extruded PVC cable jacket for durability and flexibility. To prevent moisture intrusion that could cause shorts or open circuits, a PVC heat-shrink sleeve was applied over the thermistor, creating a reliable moisture seal suitable for potable water environments.
The design was field tested and approved after successfully demonstrating performance and zero failures.

• Reliable Long-Term Operation: Proven moisture seal prevents failures even after prolonged submersion in groundwater environments.
• High Accuracy and Stability: ±0.2 °C precision supports consistent temperature monitoring essential for geothermal system efficiency.
• Simplified Installation: Color-coded 20 AWG PVC cables enable quick identification and maintenance of multi-sensor well systems.