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Marking of New
Cables

Magnetic Marking

Magnetic Marking
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Magnetic Marking

The system used by Camesa Cables U.K. Ltd, for Magnetic Marking of logging cables, is based on the equipment manufactured and equipped by Wayne Kerr and Associates Inc. of Houston, Texas.

In order to verify the accuracy of the Harks which are automatically put onto the cable with the Wayne Kerr Systems, Camesa's spooling equipment Is set up to allow us to measure the distance between any two 'one hundred foot marks', and this distance can be checked with a calibrated 100 ft steel tape measure, with a tension of 15 Ibs held on the tape.

When a cable Is to be Barked, the first three marks put onto the cable are checked with the calibrated steel tape, to ensure that the equipment Is working accurately.  On completion of the Barking operation, the final three marks' are similarly checked, to verify that the distance between Barks Is still within tolerance. A written record of the actual Measured distance between marks, both at the commencement of Barking and on completion, Is recorded on the Cable Installation/Inspection Report which Is provided to the customer with each cable serviced or each new cable Installed.

Currently, all- of our Magnetic marking Is done with the cable at a constant tension of 1.000 Ibs, and this is achieved using two capstans. A small capstan is used to hold the 1,000 Ibs Barking 'tension, and the Bain capstan is used to regulate the correct tension for spooling the cable onto the logging drum.

Since the dimensions of our workshop oblige us to use a diagonal rig up In order to have a continuous 100 ft section for checking, a correction factor Bust be applied to the weight Indicator .to ensure that the cable tension Is 1,000 Ibs. The Included angle between the cable entering and leaving the bottom sheave Is 32 degrees, so a correction factor of Cos16° must be used. The weight Indicator must therefore read 962 Ibs for 1,000 Ibs true tension in the cable.

Multiconductor logging cables have been shown to have a temperature coefficient of expansion of almost zero for a range of ambient temperatures from about 40"F to 80 T, due to the fact that although the amour wires contract with a reduction of temperature, the core similarly contracts, (and vice versa), resulting in a slight decrease In diameter, which compensates for the, length change of the amour. However a correction Bust be Bade for the difference In temperature of the steel tape at the time of checking the Barks, and the 68* Fahrenheit calibration temperature of the tape. The coefficient of expansion of the steel tape is 6.2 x 10-* per T, and the correction to be applied is:

(68°F - Actual temp.) x (6.2 x 10-⁶) x 100 = 0.00062 x (68 - T) feet

This correction must be subtracted from the indicated tape reading.

Tolerances for the marking process are as follows:

Overall accuracy that can be achieved on a 15/32 inch logging cable is 0.168 in made up as follows. (line stretch = 0.8ft/1000ft/1000 lbs)

Therefore overall accuracy is of the order of 0.1681n/100ft = 0.0141

This accuracy is within the Halts specified by major logging companies such as Dresser Atlas, and Camesa Cables U.K. Ltd alas to nark: any 15/32" logging cable to within 0.2 inches per 100 ft.

For metric measurement, cables can be marked at 50 meter or 25 meter intervals. Similar standards of accuracy apply to metric marking, and the corresponding tolerances are:

Please note that Camesa equipment is regularly checked and recalibrated to ensure that we can consistently provide levels of accuracy, which meet or exceed the requirements of our customers.

February 1987

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