TROD: Temperature Profiling Probe

Design

The TROD can generally be described as a set of six self-logging iButtons placed at fixed locations inside a 3/4 inch diameter schedule 80 PVC pipe with a solid PVC drive point and a 2 inch diameter head that is sealed to resist the ingress of water. The iButtons are connected in series to a heavy duty submersible communication cable (16 AWG Super VU-TRON Supreme Type S00W) that allows for downloading the temperature data via USB port. Without the cable, data can also be retrieved the head of the probe while the probe is submerged. We tested communication cable lengths 1.5–7.6 m (5–25 ft) with the assumption that data retrieval could occur at a variable distance to TROD. Without the communication cable, connection is made using a commercially available iButton reader (Connection Clamp, Alpha Mach, Inc). The iButtons are positioned on a printed circuit board (PCB) just beneath the head at a depths of 0.0, 0.1, 0.2, 0.5, 0.75, and 1.0 m. However, the sensor spacing and location are flexible and can be customized to any depth at an interval spacing of 0.05 m. They are positioned on the PCB to minimize the distance between the inner wall of the pipe and top of the iButton sensor where the temperature is measured.

TROD components and materials. Photo on right shows a TROD with and with out the communication cable. The extension bar was a re-purposed hardened steel grounding rod with a stainless steel bolt, nut and washer to prevent the rod from passing through the installation cap when applying force.

The TROD was designed with the recognition that the low-cost iButtons will likely need replacing every 2–4 years, depending on use. In this probe, the 6 iButtons can be easily replaced by removing the head bolt and pulling out the PCB assembly, and sliding them out of the clip holders (See a and c on the above figure). The PCB clip holders allow the sensors to be snapped into place for easy removal and replacement. The TROD design provides:

1. The ability to replace the sensors without needing any rewiring or soldering.
2. The ability to add new sensors at other depth intervals.
3. Eliminates the possibility of losing connection during field installation because once the sensors are snapped into place, they do not become dislodged. The iButtons remain at fixed locations and will not shift or move during installation or monitoring. Once reassembled, it is necessary to reapply sealant to the threads on the head bolt to prevent water from entering the TROD.

Software

A software application, WeeButton was developed specifically for the TROD to simultaneously program and download temperature data from all iButtons and export data to an Excel spreadsheet. Functionality of software also includes storage of iButton unique serial numbers, calibration corrections, and TROD identification. Therefore, upon connecting to each TROD, the WeeButton software searches for each iButtons unique serial numbers stored within the database and automatically applies the sensor specific calibration corrections. During each download, the software recognizes the TROD number and position of the iButtons and formats the output into a table with date, time, and respective calibrated temperatures for each depth. The program can customize settings for each depth on the TROD for variable time monitoring. Calibration corrections can also be provided by Alpha Mach, Inc for a small fee.