MEASUREMENT & MONITROTING
TEMPERATURE SENSORS
LABFACILITY
THERMOCOUPLE TEMPERATURE SENSORS
Where does the humble thermocouple stand
in the high-tech world of measurement
and control? The funny thing is that the
temperature instrumentation market is
dominated by complex, sophisticated
measurement and control systems which
provide a great degree of versatility and
accuracy but, in many applications rely on
a simple thermocouple (base-metal type
usually) as the temperature sensor.
Surprising really since instrumentation
is typically accurate to a fraction of a
degree centigrade whereas a base-metal
thermocouple has uncertainties of ±2oC
before it even sees the process.
Since measurement accuracy of the entire
process is only as good as that of the sensor,
why rely on something that, in principle, at
least, has not significantly changed in nearly
200 years (Thomas Seebeck discovered the
principle of the thermocouple in 1821).
Why indeed especially when you are
presented with a feeble output (typically
40µV/oC), a non-linear transfer characteristic
and the need for automatic “cold-junction”
compensation or some external ice
reference; also, one of several types must be
selected for each application, complete with
a dedicated type of extension cable.
98
PECM Issue 33
The answer to these questions is a
surprisingly simple one – nobody has yet
been able to come up with anything better
to cope with harsh environments and wide
temperature ranges.
The entire range of commonly used
thermocouple types (J,K,T,E,N,R & S) span
–200oC to 1800oC depending on their
construction; they are generally rugged
thanks to sheathing options and can operate
in corrosive media; replaceable world-wide;
reliable and, in Mineral Insulated form,
flexible and versatile. All thermocouple
types are supported by the majority of
microprocessor based instruments; they
do not require excitation since they are
thermoelectric and can operate with
reasonably long cable runs.
There are, of course, many alternative
types of temperature sensor on the market
including resistance thermometers,
thermistors, infra-red devices; all valuable
in particular applications. However, none
of these alternatives to the thermocouple
can compete in terms of temperature range,
versatility and cost-effectiveness.
Labfacility has been manufacturing
thermocouple and resistance thermometer
assemblies for over 47 years.
B ognor Regis Tel: 01243 871280
Sheffield Tel: 01909 569446
[email protected]
www.labfacility.com