Cable Deterioration
The VibWire-108 supports sensor excitation into high impedance loads. The basic sensor coil impedance is 100 ohms as standard and can be excited even when the load reaches a level of 2K ohms ie an increase of a factor 20 in the circuit resistance.
Cable type
BS 6360, class 1, 2 or 5, Instrumentation cable Low voltage
Construction
Plain annealed copper wire conductors to BS 6360, class 1,2 or class 5, PE insulation, cores twisted into pairs or triples, each pair/triple foil screened with a drain wire, overall foil screen and drain wire, LSHF sheath – Black or blue.
Conductor Plain annealed copper to BS6360 class 1, 2 or class 5
Mutual Capacitance
Collective screened cables except 1 & 2 pair
0.5mm² 0.75mm² 1.0mm² 1.5mm²
75pF/m 75pF/m 75pF/m 85pF/m
1 & 2 pair collective screened and all individual screened cables
0.5mm² 0.75mm² 1.0mm² 1.5mm²
115pF/m 115pF/m 115pF/m 120pF/m
Resistance Ohms/Km
36 24.5 18.1 12.1
Deterioration before signal failure 0.036 mm²
Category 5 Cable
Low quality cable as used in the line simulator
Mechanical Data
Inner Conductor 0.52 mm² plain copper
Deterioration before signal failure 0.09 mm²
Electrical Data
Capacitance(s) : 55nF/Km.
Inner Conductor(s) : 94 ohms/km.
Velocity Ratio : 76%.
Results
The VibWire-
Cable type
BS 6360, class 1, 2 or 5, Instrumentation cable Low voltage
Construction
Plain annealed copper wire conductors to BS 6360, class 1,2 or class 5, PE insulation, cores twisted into pairs or triples, each pair/triple foil screened with a drain wire, overall foil screen and drain wire, LSHF sheath – Black or blue.
Conductor Plain annealed copper to BS6360 class 1, 2 or class 5
Mutual Capacitance
Collective screened cables except 1 & 2 pair
0.5mm² 0.75mm² 1.0mm² 1.5mm²
75pF/m 75pF/m 75pF/m 85pF/m
1 & 2 pair collective screened and all individual screened cables
0.5mm² 0.75mm² 1.0mm² 1.5mm²
115pF/m 115pF/m 115pF/m 120pF/m
Resistance Ohms/Km
36 24.5 18.1 12.1
Deterioration before signal failure 0.036 mm²
Category 5 Cable
Low quality cable as used in the line simulator
Mechanical Data
Inner Conductor 0.52 mm² plain copper
Deterioration before signal failure 0.09 mm²
Electrical Data
Capacitance(s) : 55nF/Km.
Inner Conductor(s) : 94 ohms/km.
Velocity Ratio : 76%.
Results
For example a BS6360 type instrumentation cable of length 4 km and cross sectional area 0.5 mm2 will have to reduce 0.036 mm2 i ie to 7.2% over its original diameter before there is a failure. When shorter sensor cable lengths are involved a cable diameter smaller than 0.036 mm2 will still maintain instrument readings.
Sensor Life
Vibrating wire sensors only have a finite life and the lower the strain put onto the sensor coil the longer it will operate before failure. The Keynes control sensor excitation provides a very good compromise between sensor wear and signal strength echo response. Using a lower excitation signal but with the energy concentrated at resonance frequency ensure that the VibWire-
