The Automated Burris Gravity Meter for single and continuous observation

The Burris Gravity Meter™ manufactured by ZLS Corporation, Austin/Texas, USA, is based on the invention of L. LaCoste and A. Romberg: The zero-length spring (ZLS). A digital feedback system (range of about 50 mGal) is used to null the beam. Now, more than 120 gravity meters of this make exist worldwide and are used successfully in exploration, volcanology and surveying.

The sensor is made of the well-known (L&R) metal-alloy zero-length spring because of its low drift characteristics. The drifts observed are comparable to L&R gravimeters and are less than 0.5 mGal per month. Thus, they are much lower than the drifts known for the fused quartz sensors (e.g. of the Scintrex gravimeters).

The dial is calibrated every 50 mGals over the entire 7,000-mGal meter range. Thus, there are no periodic errors. By a fourth heater circuit temperature effects are totally avoided. The gravity meter is controlled via Bluetooth either to a handheld computer (smartphone) or a notebook computer.

The feedback responds with high stability and accuracy. The nulling of the beam is controlled by the UltraGrav™ control system which incorporates an inherently linear pulse-width modulated (PWM) electrostatic feedback system. In order to improve the handling of the gravimeter we have developed two Windows based programs which serve for the same purpose: AGESfield for single measurements and AGEScont for continuous readings.

Calibrated ultra-miniature electronic levels are used for correction of horizontal misalignment to insure accurate and reliable operation of the gravimeter. The check of the feedback on the calibration line in Hanover, Germany, provided reliable results below the 3 µGal level, and the accuracy of the calibration factor was 10^-4. The observed drifts during field measurements are very small and stable.

We will discuss some results obtained for survey measurements (single points) and continuous recording.