CableDataSheet, Cable and Wire Technical Consulting Service

i see L/R ratio at the cable catalog why we use this ratio?

Do you know this?

thanks

Actually i dont know more about signal cable but it can be below,

The L/R or inductance to resistance ratio of a cable is defined as follows:

L/R ratio = Inductance per unit length ( H )/Loop resistance per unit length (Ω)

With the loop resistance being the sum of the resistances of both conductor s to the load. Normally twice the cable length. Australian standard AS2381.7 Appendix A defines intrinsically safe system. In them associated electrical equipment is connected to the intrinsically safe electrical equipment in the hazardous area by cable. As these cable have both capacitance and inductance, they can store energy and hence maximum capacitance, inductance and inductance to resistance ratio need to be specified and known. The total cable capacitance and either the total lumped cable inductance or the L/R ratio must be less than those shown in the certificate or  installation diagram.

The L/R ratio is dependent on conductor spacing within the pair and conductors size, both of which are fixed at the design stage.Typical values
of instrumentation cable are 13 for the B50 range and 31 for the B51 range.


and.


Cables

Because cables have inductance and capacitance, and hence energy storage capabilities, they can affect system safety. Consequently the system design imposes  restrictions on the amount of each of these parameters. A great deal has been written on this subject but only rarely is there a serious limitation placed on the available cable. As cable faults are taken into account during the system analysis, the type of cable in individual installations is not closely specified in the system standard. The choice is therefore determined by the need for reliable system operation. Where intrinsically safe systems are combined in a multi-core, then there are special requirements. These determine which additional faults have to be considered.

have to search more or if someone know this maybe explain.

What is L/R Time Constant.
When a short-circuit occurs across the terminals of a DC circuit, the current rises from the load current (y In) to the short-circuit current Isc over a period of time that depends on the value of the resistance R and inductance L of the short-circuited loop.

The equation determining the current in the loop is:
U = Ri + L Di/Dt

The curve of I versus time is defined (neglecting In) by the equation:
I= Isc (1 - exp(t/t))
where t = L/R is the time constant for the rise to Isc.

Practically speaking, after a time t = 3t, the short-circuit is considered to be established, because the value of exp(-3) = 0.05 is negligible compared to 1 (see the
curve opposite).

The lower the time constant (e.g. battery circuit), the shorter the time required for the current to rise to Isc.

To express breaking capacity, the interrupted short-circuit current with the following time constants is used:
L/R = 5 ms, fast short-circuit
L/R = 15 ms, standardised value used in standard IEC 60947-2
L/R = 30 ms, slow short-circuit.