Appendix H.Commonly Asked Inclinometer Probe Questions

Can inclinometer probes be swapped freely to perform surveys in the same borehole?

Immediately after leaving the factory, probes may be swapped freely as they will meet the system accuracy specification, which is ±3 mm/30 m (±.125'/100").

Can corrections be made to the data when instruments are swapped? Such as an offset or formula?

As time passes, correcting the output of one probe to match that of another probe becomes quite difficult, and would involve a tremendous amount of time and effort spent recording, calculating, and converting every data point for every level in every survey.

Unfortunately, there is not a universal formula, any simple corrections, or offsets that can be used to correct one probe to another.

We recently sent our probe in for calibration. After receiving it back from geokon, the old surveys do not match up with the newly calibrated probe’s surveys and are showing significant displacement. It is the same probe, so why don’t the surveys match?

For the same reasons that two different probes will show differences in the same borehole, a newly calibrated probe will also show differences (from its old calibration) even though it is physically the same piece of equipment. Essentially, after a recalibration you are working with a "new" probe.

How can I compare my old data with my new data?

The recommended method to check compatibility between two sets of probes is to take at least three surveys with the new probe and compare them to the most recent survey taken with the old probe. If the resulting cumulative displacement plots performed with the new system overlay the latest survey from the old system, consider yourself lucky. However, if you see significant differences, we recommend the following method.

From the old series of surveys performed with the original system, create a final summary of cumulative displacement and a summary of displacement vs. time. Also, create a comparison of the final survey with the old system to the initial surveys taken with the new system. Then archive these summaries and data.

Next, use one of the three surveys obtained with the new system that you feel is most accurate. Use that survey to establish a new baseline survey and start a new series. This is the most accepted method in the long term.

The reason geokon recommends this method is that you already know the magnitude and rate of movements you were detecting with the old system. This will be based on the final cumulative displacement plot and the displacement vs. time summaries created earlier. When movements occur, you will catch them with the new series based on the new system.