User manual

User Manual

Data Reduction Section 5 :

The Soil Instruments tiltmeter sensor is calibrated over ±5 or ±10 arc degrees (approx. ±87

or ±175mm/metre) and has a DC voltage output dependant on tilt.

The sensors are calibrated for tilt only (please see note on temperature below) and the unit

of calibration (either Arc Degrees or mm/metre) is specified at the time of order. The

calibration certificate supplied with the sensor (please see section 6) contains the following

information:-

 Instrument Type

 Serial Number

 Range

 Calibration Data (both raw and reduced)

 Conversion Formula

 FS Error % at each calibration point

 Wiring Code

Note: As the tiltmeter is based on an IPI sensor, the calibration takes place in the IPI

calibration jigs, therefore the calibration certificate will evidence an IPI sensor, this is

quite normal and all of the factors are correct.

A positive resultant indicates movement towards the A+ (+mm) direction; a negative

resultant indicates movement towards the A- (-mm) direction.

The calibration factors can easily be loaded into a spreadsheet and data added via cut and

past or an automated program such as I-Site can be used, in which case the application of

calibration factors and gauge length is fully automatic.

The MEMS Accelerometer chip used in the tiltmeter sensor is calibrated for temperature as

part of the micro-machine manufacturing process by the chip manufacturer. As well as the

MEMS tilt element the sensor contains a microprocessor and a look up table to apply

correction for temperature changes to the silicon substrate within the sensing element. Soil

Instruments has no control over this process other than by the QA procedures followed by

the chip manufacturer, which specify the correction and rejection criteria.

The sensor output is therefore corrected automatically for the effects of temperature on the

accelerometer chip. Please note that this correction will not apply to unknown factors within

the sensor string or borehole where an external change may well be occurring. Soil

Instruments do not offer the sensor with an on-board temperature sensor. If temperature

measurement is desired, then a separate temperature sensor must be installed additional to

the tiltmeter sensor.