Introduction

The new sensor eliminates the cross-coupling errors inherent in older beam-type gravity meters by constraining the proof mass to vertical linear motion.

Damper adjustments are no longer required.

The new sensor utilizes liquid damping that virtually eliminates the sensitivity to vibration common in air-damped sensors.

Residual imperfection errors, due to minute variations in manufacture of the system are typically three to five times smaller than those for beam type sensors. Unlike beam type meters, imperfection errors are stable with time and do not require regular testing to track changes.

The new design eliminates the “slope error” prevalent in beam meters that causes reading errors with beam position under dynamic conditions.

The host computer stores all data on hard disk and can simultaneously direct data to the video monitor, serial port, and printer in a variety of formats. Either a numerical or graphical format may be selected for display on the printer. In high-resolution marine and airplane modes, raw data are recorded once per second, allowing the user to custom filter the data for specific applications. In marine mode the data are filtered in appropriate manner for marine data and recorded at 10-second intervals.

Additional external data may be appended to the gravity data. The system accommodates up to four analog channels and a 24-bit digital channel. The system is fully automatic and will start unattended after a power interruption. Operation is as simple as turning on the switch. However, all system functions can be controlled manually through menu selections. All keystrokes are logged in a separate file for a complete record of system activity. System functions are continuously monitored and UltraSys will automatically shut down and activate an external alarm signal in the event of a serious malfunction.

UltraSys is Fully Digital

Transducer outputs are digitized with little additional analog processing. The ZLS system digitizes input signals 200 times a second. All processing, including filtering, is done digitally. All control-loop algorithms, for both the platform and gravity sensor, are performed digitally by an embedded computer. Eliminating analog circuits enhances reliability and simplifies servicing.

A Mature System

Herbert D. Valliant, co-founder of ZLS Corporation, developed the prototype at the Geological Survey of Canada (Geophysics, 50, 840-845, 1985.)

Accuracy of the Operating System

The accuracy of a marine gravity meter is difficult to specify as it is dependent on the characteristics of the ship, the sea-state, and accuracy of navigation (typically 1mGal).

ZLS’s full digital control system enhances overall system accuracy by eliminating the gain and offset drifts that are inherent with analog electronics. It permits the platform and sensor control parameters to be set more precisely. In analog systems, these parameters are adjusted by changing electronic components, whereas, in digital systems, they are adjusted by simply entering a number in the computer.

Specifications

Sensor

Type: Metal Zero-Length Spring hardened metal micrometer screw

Range: Worldwide 7,000 mGal marine

Temperature range: -15 to +50° C

Drift: 3 mGals or less per month after aging

Static Repeatability: <0.1 mGal

Stabilized Platform

Pitch: +/- 25 degrees

Roll: +/- 30 degrees

Period: standard 4 minute, optional 16 minute

Damping: 0.707 of critical

Control System

Power Requirements: 87 to 270 VAC   47 to 63 Hz single phase
Power Consumption: Operation: 1 Amp*, Maximum: 2.5 Amp* *measured at 117 Volts @ 60 Hz.
Resolution of Recorded Data: 0.01 mGal
Clock and Gyro Power Source: Frequency: 200Hz
Temperature stability: 5 ppm  -20°C < T < +70°C
Short term aging: 1 X 10^-9/sec
Adjustability: Sufficient for 5 years of aging.

External Outputs

Digital: 24 bit TTL compatible input
Analog: 4 channels, 16 bit resolution, gains of 1, 2, 4, or 8 may be selected by menu

Sample rate 200 Hz

Deliverables

• ZLS Dynamic Sensor

• ZLS Stabilized Platform

• System Control Module: attaches to the platform frame

• Universal Worldwide Power Supply: freestanding

• Host Software: processes data for high resolution or standard marine operations

• Comprehensive User’s Manual

• Limited two-year warranty

Dimensions

Stabilized Platform and Sensor: 27 in wide; 22 in deep; 25 in high (70 cm wide; 55 cm deep; 64 cm high)

System Control Module: 19 in. wide; 5.5 in. deep; 3.5 in. high (48 cm. wide; 14 cm. deep; 9 cm. high)

Power Supply Module (Desktop Package): 21 in. wide; 18 in. deep; 7 in. high (53 cm. wide; 46 cm. deep; 18 cm. high)

Specifications are subject to change without notice. Results may vary depending on conditions.