• FEATURES: The remote controlled tidal superconducting gravimeter (RSG) is a major advance in the design of the superconducting gravimeter. Compared to previous superconducting gravimeters, it offers:

• Reduced size - it is easily moved and fits in most geophysical or seismic stations;
• Integrated electronics and data system - all control electronics have been redesigned to increase long-term stability and to reduce noise and response to temperature changes;
• Remote control - a single user can control and monitor multiple remote instruments from his home office or laboratory;
• No liquid helium refills - after an initial fill with liquid helium, the system will operate indefinitely without any need to refill with liquid helium;
• Simple and infrequent maintenance required - typically 10,000 hours between preventative maintenance visits.

USES: Combined with the well known high sensitivity and long term stability of the superconducting gravimeter, these features make the RSG the ideal choice for:

• Short term (1 to 6 month) and long term tidal measurements to map variations of tidal loading versus geographic location;
• Operation at a site of sudden geophysical interest produced, for example, by the appearance of volcanic or earthquake activity;
• Extended operation at remote sites where it is difficult or impossible to obtain liquid helium;
• Measurement of long term secular changes of gravity associated with crustal uplift, water table variations, oil and gas reservoir depletion and hydrothermal aquifer condition.

DESCRIPTION: The RSG design is based on the gravity sensor used in the GWR Compact Tidal Gravimeter which is currently being operated worldwide. However, major improvements have been made to simplify use, increase reliability and reduce manpower requirements. All major subsystems of the RSG, including the gravity sensor, electronics and data system, may be controlled remotely via computer modem. Additionally, changes have been made to the design and operation of the instrument which eliminate the need for highly-trained personnel to be present at the remote site in order to set up and operate the instrument. To begin operation, the instrument is first moved to the remote site of operation, set in place and roughly leveled using two micrometers. Next, the cryocooler is inserted into the neck of the dewar. This Gifford-McMahon type cryocooler uses an advanced regenerator and provides substantial cooling power at 4.2 ^OK. Its mechanically-driven piston offers superior cooling performance, as well as greatly reduced noise and vibration compared to previous gas driven cryocoolers. Within hours after application of power, the lower stage of the cryocooler operates below the vaporization temperature of helium so that the evaporated helium gas is re-condensed and drips back into the dewar’s storage reservoir. Therefore, during normal operation, the system consumes no liquid helium. During power failures, evaporated helium can be stored in helium recovery bags and reliquefied when power returns. In this way, the dewar’s 25 liter storage volume protects against power failures without any need for on-site operator intervention.

Maintenance of the cryogenic refrigeration system requires replacement of the compressor adsorber annually and replacement of the coldhead every three to five years. Both procedures are straightforward and simple to perform and do not interfere with the continuous gravity data record. After being rebuilt at the factory, the cryocooler can be used for the next maintenance exchange. The RSG requires no other scheduled maintenance.

After the system has been placed at the remote site, it can be initialized by either an on-site operator or remotely by computer modem. All required operations, including: sphere levitation, fine tilt alignment and centering the signal at the mean of tidal variations can be completed automatically or manually by the remote user. After a month long record is obtained, the data can be analyzed to determine the most important station parameters. These parameters can then be used to predict tidal variations and to subtract them from the data. Daily, weekly, or monthly examination of differences between predicted and actual gravity enables the user to examine gravity variations at the sub-microgal level, practically in real time.

The RSG has the same low noise and low drift specifications achieved with the earlier Compact Tidal Gravimeter. Now, with the addition of remote control, simplified operation and a dewar that requires no liquid-helium refills, a single user can operate an array of superconducting gravimeters from any convenient location.

SPECIFICATIONS:

Specifications subject to change without notice

PRICES:

Single Sphere RSG................................................Consult Factory

Dual sphere RSG: ..................................................Consult Factory