Dynamic Meter Upgrade for L&R Air/Sea Gravity Meters

The ZLS Dynamic Meter Control System, UltraSys™

The ZLS Control System for L&R Air/Sea Gravity Meters – Improves Accuracy, Increases Efficiency, and Enhances Reliability


UltraSys™ Highlights

  • Large (55 conductor) main cable eliminated.
  • High resolution marine and airplane modes.
  • New DC heater control circuit.
  • Smallest and lightest system available.
  • Completely automatic.
  • Greatest precision.
  • Fully digital control system.
  • 200 Hz sample rate.32 bit processor; 16-bit A/D and D/A.

UltraSys™ is Fully Digital

Transducer outputs are digitized with no additional analog processing.  The new 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: Accurate and Reliable

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 a 32-bit embedded processor to perform all of the platform and sensor control functions.  The system control module is attached to the platform frame, thereby eliminating the 55 conductor main cable that connected the sensor to the computer in older systems.  The power module may be located anywhere near the platform.  A host computer 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.  The embedded computer calculated the cross-coupling monitors at a 25 Hz rate.  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 record at 10-second intervals.

Additional external data may be appended to the gravity data.  The system accommodates up to four analog channels and 24 digital channels.  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 key strokes 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.

ZLS Upgrades the Sensor and Platform

The Gimbal Assembly

The gimbal mechanism is completely disassembled and cleaned.  All moving parts are examined and replaced as necessary.  Bearings, shock cords, shock mounts, level adjusters and damaged frame members are replaced.  All metal fittings are replaced with stainless steel counterparts.  The gimbal cable is replaced with a new, more flexible cable manufactured from materials resistant to oil and salt water.

The Sensor

The sensor is fully tested and adjusted for optimum performance using the ZLS test facility.  All moving parts are examined, cleaned, lubricated, and replaced when necessary.  All internal work is done in the ZLS clean room.  Original point-to-point wiring is replaced with printed circuit boards.  The optical beam position sensor is replaced with a capacitance position transducer.  The synchro motor is replaced with a stepping motor.  Anomalous heat sources near the sensor are removed to provide better temperature control.  An improved sealing system featuring metal tubing and backfilling with dry nitrogen eliminates the need for pressure equalization at sea.  This prevents the accumulation of contaminants in the sensor and assures greater reliability and accuracy.

Features of UltraSys™

  • 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.
  • 25 Hz computation of cross-coupling monitors assures accuracy.
  • 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 and provides a remote alarm signal in the event of a serious system malfunction.
  • Keyboard log records all keyboard activity for review.
  • Complete testing and final adjustment using the ZLS test facility for vertical, horizontal circular and ramp testing.
  • Self-contained precision gyro power supply and servo amplifiers.
  • Two-year limited warranty.


  • System control module – attaches to the platform frame.
  • Universal worldwide power supply – freestanding.
  • Host computer software – processes data for high resolution or standard marine operations.
  • Dot-matrix color printer (optional).
  • Complete calibration of cross-coupling parameters.
  • Host computer (optional).
  • Upgrade of gimbal assembly.
  • Upgraded junction box – attaches to sensor.
  • Sealing of the gravity sensor and backfilling with dry nitrogen.
  • 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 components, whereas, in digital systems, they are adjusted by simply entering a number in the computer.

Users of the ZLS system have reported accuracies (rms differences from ground-truth data measured with a bottom gravity meter) substantially better than one mGal.


Outside Dimensions

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



System Control Module: 6 lb. (2.7 kg.)
Power Supply Module (Desktop Package): 36 lb. (16 kg.)

Power Requirements:

87 to 270 Vac 47 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:

Frequencies available: 200, 400 and 800 Hz
Temperature stability: 5 ppm -20C < T < +70C
Short term aging: 1 X 10-9/sec
Optional Rubidium Time Standard available

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:

Windows XP

Minimum Clock Rate: 900
Minimum RAM: 128 Mb
External Storage: CD ROM
One Serial Port:* RS_232



Processor: 80386DX
External Storage: Floppy
One Serial Port:* RS_232

*A second serial port is required to transmit data serially. A USB to Serial adapter is acceptable.

Limited Warranty

A two year warranty including parts and labor is provided on all ZLS services and parts. Exceptions include new original equipment, such as the computer and the gyros, where original warranties are passed on to the purchaser. The warranty does not include damage or other faults due to negligence. As cross-coupling parameters are subject to rough handling during shipment, ZLS does not warrant the cross-coupling calibration. ZLS will, however, perform cross-correlation analysis free of charge during the warranty period and, if necessary, supply revised cross-coupling coefficients based on this analysis. Any software updates issued by ZLS during the warranty period will be supplied free of charge.

The following are trademarks or registered trademarks of their respective companies or organizations:
DOS, Windows / Microsoft Corporation
QNX / QNX Software Systems, Ltd.
UltraSys™, ZLS Logo / ZLS Corporation

Specifications are subject to change without notice.

7801 North Lamar Blvd. Suite E-184 | Austin, Texas 78752 USA | Phone: 512-453-0288 | Email: info@zlscorp.com

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