| 1 |
MEASURING OF ELECTROSTATIC EFFECTIVENESS OF SHIELD : This can be done through Noise Rejection Ratio test. This NRR Test is a type test which establishes the efficiency of element shield & hence should be offered for cables with shielded individual pairs/triads. |
| 2 | SIGNIFICANCE
OF CABLE IMPEDANCE FOR UNDISTORTED TRANSMISSION OF SIGNALS: It
is necessary that the cable has a matching Impedance as that of
terminal devices, since a mismatch can lead to serious distortions
of signals.
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| 3 |
COMPATABILITY OF IS:1554 FOR SIGNAL & INSTRUMENT CABLES : IS:1554 is essentially a standard for Unshielded Power and Control Cables. It therefore is not adequate for specifying even the most ordinary Signal & Instrument Cables leave alone the Intrinsically Safe Circuit Instrument Cable. |
| 4 | PVC
TEMPERATURE RATINGS DEFINED IN EUROPEAN STANDARDS : Due to prevailing climatic conditions, Ambient Temperatures rarely shoot up beyond 25-30ºC in European countries. Hence European Standards prefer to specify lower range of Temperature Ratings for PVC used in cables. For application in tropical countries, it is necessary that one refers to the relevant Indian Standards. |
| 5 | VOLTAGE
GRADE FOR SIGNAL & INSTRUMENT CABLES : Many times, consultants specify a voltage grade of 1100 V for Signal & Instrument Cables. Pair/Triad
Instrument Cables with Individual and/or Overall shielding carry
signal energy levels in the range of 4 to 20 mA/4 to 20 mV and as
such, voltage grade of 300/500 as specified in BS:5308 is more than
adequate. What is most important for such cable is to have adequate
insulation resistance BETWEEN ADJASCENT SHIELDS/ARMOUR since that
alone ensures signal integrity and performance. |
| 6 |
ADVANTAGES
OF MULTI-STRANDED DRAIN WIRE :
For shielding, drain wire in the form of fine wire bunched Tinned Copper conductor is far more effective and functionally integral because of its flexibility and improved contact area with shield as compared to a Solid or less flexible drain wire. |
| 7 | EFFECTIVENESS
OF BRAIDED SCREEN : Effectiveness of braided screen depends on the coverage offered by the braiding. Marginal reduction in fill factor (coverage) of Copper braiding may reduce cost substantially but, seriously compromises the critical parameters of these cables. |
| 8 | THERMOCOUPLE
CABLE - EXTENSION OR COMPENSATING ? Except for B type, Extension Cable is made essentially of the same Alloy as the thermocouple element which makes the cable far more expensive than the Compensating Cable which offers comparable thermal emf characteristics at much lower costs. |