For use with ASAMS 3 and 12.
This instrumentation package is designed to enhance the integrity of sub-sea MPI by enabling measurement of magnetic eld strength, ambient visible light, and ultra-violet irradiance with a single sub-sea module. It has been proven over several years service in the North Sea and elsewhere. In practice, it allows the user to replicate previous work-face MPI conditions on subsequent inspections, thus reducing the probability of spurious or missed indications. Initial inspections benet from using a known and measured set-up. Power is from internal Nickel Cadmium cells, which will give in excess of 20 hours continuous use, recharging taking about 12 hours from ‘Battery Low’ indication.
The charging circuitry has been enhanced to give effectively penetratorless charging, the stainless steel switch knob being used as one contact and the grab-ring the other. Internal electronics double-isolate these contacts to ensure that no current can ow OUT of them, thus preventing both external discharging via the contacts and damage from charger misconnection. Additionally, a fuse has been incorporated within the battery pack that provides protection against both short circuits and excessive charging currents. Total safety is therefore ensured, and the elimination of a waterproof connector for charging provides cost and reliability advantages to the user.
The display is a 12.5mm back-lit Liquid Crystal, and ranges are selected by a rotary switch. This switch has no detents, and no end-stops, thus minimising the potential of damage by abuse. The selected range is clearly shown by indicators on the unit, as is the ‘Low Battery’ condition. The magnetometer is a surface magnetometer, working on AC elds and is generally thought to be the only type of device that will measure the eld below the surface of the parent metal. Other devices, such as Burmah-Castrol strips and Hall-Effect magnetometers can only detect the eld above the surface of the metal, and this will vary signicantly with proximity. By requiring a physical contact with the work-face, and only measuring the eld within the parent metal, the HCL magnetometer reduces the potential for inadvertent operator adjustment of the readings by manipulating the device in place of adjusting the eld current. Calibration is traceable via NAMAS certied test pieces.
The housing is machined from solid aluminium alloy, hard anodised to Defence Standard 03-26/2. It is tted with a stainless steel ‘grab-ring’ that serves to protect the port, penetrator and switch knob, and provides a handle, a tie-off point and the negative charging electrode. The grab-ring is sacricial, and in cases of severe impact is designed to deform and absorb the shock, thus protecting the pressure hull. Use of this instrumentation will allow diving contractors to ensure consistent standards of MPI, and its specication by structure will provide them with additional confidence in MPI results.