Digitilt AT System FAQ
Yes, if you upgrade your DigiPro software to DigiPro2. DigiPro2 can import all of your classic surveys. After that, you can keep AT surveys and Classic surveys in the same project database; however, it is not recommended that surveys taken with one probe (classic or AT) be compared to initial readings taken by another probe (classic or AT).
No. The Classic probe is analog and the AT probe is digital. They have different power requirements and different readouts. Thus they are not freely interchangeable.
We do not recommend interchanging probes, in any case. Differences between probes are amplified by tilt and curvature of the casing, even with probes of the same type. The AT system features new cable marks and a cable gate, which introduces even more differences.
Best Practice: Some users obtain separate baseline surveys with two systems: an "active" system and a "backup" system. Subsequent surveys are taken with active system only. If that system fails, the backup system and its baseline survey can be used to continued the monitoring program. In this scenario, AT and classic systems would work well as either active or backup systems.
Yes, there are three main differences:
- AT cables are lighter and easier to carry, but permanently attached to the cable reel.
- AT cable marks are designed to work with a cable gate.
- AT cable marks are measured from the top wheels of the probe, rather than the middle of the probe.
The AT system displays readings as mm or inches of tilt, and this reading applies at the depth of the top wheels. Scroll downwards to see a technical explanation with a graphic. Classic cable marks are measured from the middle of the probe, but this has some unexpected effects when readings are plotted:
- AT system: A reading taken at 10 m is correctly plotted at 10 m, as you would expect.
- Classic system: A reading taken at 10 m is correctly plotted at 9.75 m, which you would not expect.
- AT system: A reading taken at 30 feet is correctly plotted at 30 feet, as you would expect.
- Classic system: A reading taken at 30 feet is correctly plotted at 29 feet, which you would not expect.
The cable gate provides an easy way to align cable marks to the top of the casing. With the pulley assembly, depth marks are typically aligned with the cleats at the top of the pulley, which is 0.3m or 1 foot above the top of the casing.
- AT system: When the cable mark shows 10 m, the probe is 10 m down hole.
- Classic system: When the cable mark shows 10 m, the probe is only 9.7 m down hole.
- AT system: When the cable mark shows 30 feet, the probe is 30 feet down hole.
- Classic system: When the cable mark shows 30 feet, the probe is only 29 feet down hole.
Summary: If classic surveys are not corrected for the pulley offset and the middle of the probe measurements, plots will show displacements a full interval deeper than they actually are.