Calibration of Soil Instruments Inclinometer System
This article further explains our recommendations for calibration of our Inclinometer systems and how checks can be performed to test the accuracy of our Inclinometer system
2. Recommended calibration frequency
Calibration is completed to ensure the accuracy of the Inclinometer is of a high standard, the UK market dictates that Digital Inclinometer systems should be calibrated annually however this is not always the case and varies from site to site.
To remind the user that the system should be calibrated, after 12 months from the last calibration, when In_Port is started on the field PC a warning message will appear. To keep work interruption to a minimum, this message will appear once every 7 days. This message can be cleared by tapping the confirmation tab below the message and the system will then respond completely as normal. It is recommended though that the system is returned for calibration as soon as possible.
3. Why inclinometers require calibrations
There are a few things that this will depend on. Firstly this will depend on the amount of use that the inclinometer is subjected to; if the Inclinometer is used heavily then the rate of general wear and tear in the Inclinometer will be increased.
A further consideration on how regularly the Inclinometer will need to be calibrated is how well it is maintained. Recommended maintenance of an Inclinometer system varies from wiping off dirt and moisture from the probe and cable after use and checking that the Inclinometer probe is mechanically sound and lubricate the wheels with light machine oil to remembering to lubricate the wheels prior to every use. Soil Instruments also recommends always ensuring that the Inclinometer and field PC are protected from shock during transit. Although the system is robust, dropping the probe may cause damage to the sensors, always secure the probe in the probe holder on the cable reel.
4. How to check if your inclinometer requires a calibration
Essentially there are two ways that you can check if your Inclinometer would benefit from a calibration. The most easy and apparent method of checking your Inclinometer is to use the checksums presented on screen when taking readings in the A180 direction. The readings screen on the field PC shows two checksum boxes when recording you 180° readings. 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 value 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, given the accuracy of the readings presented, it is highly unlikely that the probe will be positioned in the exact opposed position, so the readings are never exactly opposite values. Primarily the checksums are of use to the user 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 system is not showing any sign of fault 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. It should also be considered that if readings are taken close or on a casing joint, then checksums for these readings may not be repeatable, if all of the other checksums are consistent, then this also is quite normal. We generally recommend that if the checksum values consistently exceed 5mm then this could indicate a deterioration in the condition of the Inclinometer system and we recommend that the system is returned for an inspection and calibration.
A second method of checking whether your Inclinometer has drifted since its last calibration is by using a Soil Instruments Reference Frame (catalogue code C10-3.8). If you do not have a Reference Frame and would be interested in purchasing one please either contact sales for a quote or let us at the support centre know and we shall forward on your request. The Reference Frame allows the user to systematically cycle through three positions (-10deg, 0deg, +10deg) comparing the results from the field PC screen to the results on the Inclinometer calibration certificate allows the user to check if the readings correspond or not correspond depending on whether the calibration is still valid.