Knowledge Base

Checksums or face error message (see Figure.1) is a way of the Inclinometer communicating to the user that the readings they are receiving may not be what they are expecting. A "face error" message this indicates that the checksum value is outside of the recommended threshold for the C17 Digital Inclinometer System.

The readings screen on the field PC shows two checksum boxes. The checksum is the 0° direction reading (e.g. A+) at each depth added to the 180° reading (e.g. A-), in an ideal world, these two readings would be exact opposites of each other and cancel out, giving a checksum of zero. In the real world however checksums are rarely zero due to manufacturing tolerances in the probe and very small differences in both the 0° and 180° position of the probe wheels, in other words, the probe is never exactly in the same place, so the readings are never exactly opposite. Where the checksum is of use to the user is as a check that all depths have been correctly read for 0° and 180° (if a depth is missed, the checksums from this point will be very large) and that the probe is not showing any sign of deterioration as the checksums at each depth should be (a) roughly the same, and, (b) consistent along the length of the borehole.

Checksums should only be a concern, no matter what their actual numeric value, if they fall outside the parameters above. Please remember that if readings are taken about a casing joint, then checksums for these readings may never stabilise, if all of the other checksums are consistent, then this also is quite normal.

Figure 1. Face error message

2. Increasing Checksums and the Possible Causes
Increased wear and tear on the Inclinometer System. Wear a tear can be caused due to minimal maintenance of the Inclinometer probe. The probe should be cleaned and maintained at regular intervals, generally after each days use. This is described in section 7.01 of MAN-180 supplied with each unit. The user should ensure the wheels are in good condition, have no wear or flat spots, and they spin freely. The user should also ensure that the wheel arm’s spring back into place without resistance. If they do not, the user should free the wheels and wheel arms by applying the oil supplied. If this has little effect then contact us. 

Another common cause for gradual increases in checksum errors can be due to damage to the probe. These systems are often used in harsh environments, if the probe has experienced a knock/drop or has not been transported correctly the systems checksum value may increase. This is a mechanical influence that can only be repaired by returning the system for service/repair.

An important variable of checksums is the repeatability of the checksum value i.e. it should remain consistent. If the checksum value is not repeatable, this indicates a possible issue with the Inclinometer or there is a strong possibility that the probe is not currently at the correct depth. Please ensure that the probe is raised through each depth and no measurements are missed throughout the reading process.
If your Inclinometer's checksums are gradually increasing, the issue may be due to maintenance and general wear and tear on the probe. To alleviate this we recommend a yearly calibration of our C17 Digital Inclinometer Systems. 

3. Tests to perform if you believe there to be a problem with your Inclinometer
If the error message persists or you believe that there is an issue with your Inclinometer we advise running a short bore hole run of 5 metres and sending us the RPP files to examine further, as well as the borehole runs that you believe there to have been issues with.