Index Austin

Further Information

Introduction

After nearly three years of research and development, ZLS has introduced a meter for airborne and marine applications. The ZLS Dynamic Meter™ is a completely new meter designed to eliminate inherent cross-coupling errors, frequent damper adjustments, and vibration sensitivity problems associated with beam-type gravity meters.

Features of The ZLS Dynamic Meter™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.

UltraSys™ Control System

UltraSys^TM is Fully Digital Transducer outputs are digitized with little or no 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.)

How UltraSys™ Functions UltraSys™ utilizes an embedded processor to perform all of the platform and sensor control functions. The power module may be located anywhere within 3 meters of the platform. A host computer, connected to the control module with a serial cable, completes the system.The embedded processor is connected to a host computer through a serial port. Using ZLS-supplied software, the host computer processes the data as required for high resolution or standard marine operations and archives the final data. Raw data from the accelerometers, gyros, and gravity transducer are digitized 200 times a second with a 16-bit A/D converter and processed by the embedded computer. Analog signal outputs to control the motor and gyros are provided by a 16-bit D/A converter, which is also updated at 200 Hz. Slightly filtered data are transmitted to the host computer once per second.

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 in the event of a serious malfunction.

Features of UltraSys^™ Controller System

Advanced control system uses an embedded processor.

Digital techniques replace analog hardware, eliminating electronic drift and enhancing system reliability.

Fully automatic system will start and function unattended after a power interruption.

Full manual control through menu selection.

200 Hz data sample rate accurately digitizes sensor, gyro and accelerometer signals assuring no loss of signal information.

200 Hz update of platform feedback loops provides superior platform control.

Simultaneous data output to video monitor, hard disk, serial port, and printer.

Graphic or digital format may be selected for printer output.

Alarm function shuts down system in the event of a serious malfunction.

Keyboard log records all keyboard activity for review.

Complete testing and final adjustment using the ZLS test facility.

Self-contained precision gyro power supply and servo amplifiers.

Two-year limited warranty.

ZLS GyroPack™

The ZLS GyroPack™ provides a cost-effective replacement for the traditional Honeywell GG49 gyro used on L&R dynamic gravity meters. The GyroPack™ comprises a modern two-axis dry-tuned gyro and companion servo board. The gyro is claimed to have an MTBF (mean time before failure) in excess of 70,000 hours at 70° C (approximately 8 years). Unlike floated gyros (i.e. GG49) the dry-tuned gyro is not degraded by on-off cycles. Unlike fiber optic gyros (FOG) the dry-tuned gyro does not slowly deteriorate causing a time dependent degradation of the gravity meter platform.

In the unlikely event that a gyro fails, the complete GyroPack™ may be replaced with a spare unit at sea. Simply remove three screws, remove the old, and install the new GyroPack™. No alignment procedures are required.

It is not advisable to change the gyro itself at sea because mating the gyro to its companion servo board should be performed on a stable surface. Although it is possible for users to replace gyros themselves, ZLS will perform this service for a modest charge.

Deliverables

ZLS Dynamic Sensor

ZLS Stabilized Platform

Spare ZLS GyroPack

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 manual

Limited two-year warranty

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.

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: Zero-Length Spring Hardened metal micrometer screw

Range: Standard: Worldwide 7,000 mGal Marine Optional: Worldwide 10,000 mGal Airborne

Temperature range: -15 to +50 C

Drift: 3 mGal or less per month after aging

Static Repeatability: 0.2 mGal

Stabilized Platform

Pitch: +/- 25 degrees

Roll: +/- 25 degrees

Period: Standard 2 or 4 minute, Optional 16 minute

Damping: 0.707 of critical

Accuracy at Sea

Accuracy of the ZLS Dynamic meter is difficult to specify, as it is dependent on the characteristics of the ship, the sea-state, and accuracy of navigation (typically better than 1 mGal).

Control System

Power Requirements: 87 to 270 Vac to 63 Hz single phase

Power Consumption; Operation: 1 A*, Maximum: 2.5 A (measured at 117 Volts 60 Hz)

Resolution of Recorded Data: 0.01 mGal

Clock and Gyro Power Source Frequency: 200Hz

Temperature stability: 5 ppm

Short term aging: 1 X 10-9/sec

Adjustability: sufficient for 5 years of aging.

External Inputs:

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

Minimum Host Computer Requirements:

80386 or compatible with math coprocessor and hard disk.

DOS and Windows operating systems are supported.

Dimensions and Weights (Outside Dimensions)

Dimensions:

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

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

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

Weight:

Stabilized Platform and Sensor: 185 lb +/- 5 lb (83.9 kg +/- 2.3 kg)

System Control Module: 6 lb (2.7 kg)

Power Supply Module (Desktop Package): 36 lb (16 kg)

Specifications are subject to change without notice.
Results may vary depending on conditions.
The following are trademarks or registered trademarks of their respective companies or organizations:
ZLS Dynamic Gravity Meter™ and UltraSys™, ZLS Logo / ZLS Corporation.
DOS, Windows / Microsoft Corporation.