SPECIAL HI-TECH CABLES
The measurement of temperature
is becoming important in many fields of activity. The needs of
better techniques and improved accuracy is also constantly present.
Extension cables are a convenient
and frequently economic way of extending thermocouple circuits
from the sensor to the reference unit in the form of wiring cables
with similar conductor materials to those of the sensor. Alternatively
they may incorporate quite different conductor (alloys) materials
which in combination develop similar out puts to be experienced
at the thermocouple to extension wire connections, where ever
compensating cables are having cheaper alloys of different types
in combination match the thermocouple characteristics as closely
as possible, but over a limit temperature ranges.
An obvious example of the use
of compensating cables is with platinum. Metal thermocouple where
the cost of the thermocouple materials is high and it is usually
an economic necessity to extends the circuits using lower cost
compensating cables, however if the temperature of the connecting
box is allowed to increase the out put from the compensating
wire will be diverge from that of the platinum thermocouple and
errors in the temperature determination will increase correspondingly.
Another example of the use
of compensating cables is where the output of 'K' type thermocouples
is closely matched at low temperatures by the combinations of
Cu/Cu-Ni alloys. As one conductor is already copper the number
of reference junctions is halved, an advantage with large multi-thermocouple
schemes. The loop resistance of this cables is also same what
less than with the equivalents 'K' type thermocouple alloys.
Extension cables are produced usually in a convenient form for
carrying over long distances e.g. as wire cables or multi-core
cables, with extension cables this mismatch errors arising from
high connecting box temperature are likely to be less than with
compensating cables.
Note : These cables are available in various
insulations i.e. PVC, HR-PVC, FRLS-PVC, Fiber Glass, PTFE (Teflon)
& Rubber Compound.
