- What temperature range
should I work with?
- Do I need a
quick reading?
- Do I need accurate data measurement,
or is an approximate measurement sufficient
?
- Do I need to measure the intrinsic temperature of the
material and therefore in contact with or at the
surface?
- What is the environment in which the process to
which the probe is connected is taking place?
- What type of instrument do I need to connect the probe to,
and what type of sensor does it support?
These questions will provide answers that
will easily lead me to the right choice between
a thermocouple and a resistance thermometer:
Why
choose a
THERMOCOUPLE:
ADVANTAGES:
- various sizes
- wide range of detectable temperatures
- high data response speed
- low cost
DISADVANTAGES:
- lower accuracyin
data detection
- expensive wiring as it requires the use
of cold solder compensation cables (compensated cables
)
The working environment also has a significant impact on the
operating mode of THERMOCOUPLES. In fact, as we have noted, one of the
questions to ask when choosing a probe is
what environment we are working in. Why
this? Simply because the various types of probes (THERMOCOUPLES in
this case), in addition to differing in terms of the temperature range
measured and the type of material they are made of in order to
work at various temperature ranges, show
differences in durability depending on the type of environment to which they are
exposed; they are divided into:
TIPOLOGIA
AMBIENTE DI
LAVORO
COMPOSIZIONE
CHIMICA
RANGE TEMPERATURA
-
J
atmosfere riducenti e
vuoto
ferro/costantana
da
-100 a 760°C
-
K
atmosfere neutre o
ossidanti
chromel/alumel
da -100 a 1260°C
-
T
atmosfere riducenti, inerti/sottovuoto,
ossidanti rame/costantana
da -200 a 400°C
-
N
sostituiscono le tipologie K in ambiti
gravosi nicrosil/nisil
da -100 a 1260°C
-
E
atmosfere inerti o
ossidanti
chromel/costantana
da -200 a 1000°C
-
R
atmosfere in alte temperature usate nei processi
industriali
platino-rodio
(13%)/platino
da 260°C a 1760°C
-
S atmosfere
in alte temperature usate nei processi di
laboratorio platino-rodio
(10%)/platino da
260°C to 1760°C
-
B
atmospheres at high temperatures exceeding
types ‘R’ and ‘S’ platinum-rhodium
(30%)/platino-rodio (6%) da 870°C a
1820°C
-
C atmosfere a
vuoto
spinto
tungsten-rhenium
(5%)/tungsten-rhenium (26%) from 0°C
to 2315°C
Why
choose one
HEAT RESISTANCE:
ADVANTAGES:
- high precision in detecting
data
- simple wiring possible using
simple copper wires
- good stability
DISADVANTAGES:
- limited temperature range
- sensitive to vibrations
- power supply required
- high cost
What are the main
types of
THERMAL RESISTANCE?
Essentially, thermoresistances are
classified according to the type of material used in
their composition, which can be PLATINUM
(Pt) or NICKEL (Ni). Of the two types, the
most commonly used is the former, i.e. PLATINUM, because, unlike
NICKEL, it has excellent corrosion resistance and
long-term stability, as well as a good
measurable temperature range, from -200 to +850°C. The alternative
to NICKEL is lower in terms of production costs,
but it is less stable over time, showing lower measurement accuracy
at high temperatures. It should also be noted that
NICKEL thermoresistances have a lower measurable temperature range,
ranging from -80 to +260°C.
Thermocouples can be
configured in three different variants,
namely::
- 2-wire:
mainly used where accurate
measurement precision is not required and on short connection sections
- 3-wire:
used where more accurate measurement precision is required
and on medium-long connection sections
- 4-wire:
used where high measurement accuracy is required
The most commonly used thermoresistances
are the so-called PT
100
and
PT
1000, respectively
‘PLATINO 100 ohms and PLATINO 1000
ohms’, where the values 100 and 1000 ohms are the measured resistance of the
probe at 0°C.
There are also two other
types, the
probe
NTC and the
PTC probe,
which differ from each other simply in the way
they detect temperature, as the
NTC
varies its internal resistance,
decreasing it as the temperature increases;
the opposite of its ‘sister’
PTC which
increases in direct proportion
to the increase in the
detected temperature.
- When the
‘NTC’ type is used and when the
"PTC
":
Usually, the
NTC is
used in the measurement of internal temperatures of
food, fluids, boilers, refrigeration units
(refrigerators/air conditioners), while the PTC
is usually used as a thermal ‘safety’ device
,
applied to motors, overcurrent control, small
heating appliances (hair dryers, toasters, etc.), and used
precisely as a signal for a thermal safety switch
.
Knowing the advantages and disadvantages of the various
types of probes, thermocouples or thermistors, contact or
infrared, PTC or NTC, it can be deduced that THERE IS NO
EXIST one type that is better or
worse than another; you simply need to understand which is the
right sensor for the process to which it will be
applied.
