Platinum
resistance elements are temperature sensors for resistance thermometers.
They cannot generally be used in their basic element form but must be
built into some type of assembly which will enable them to withstand the
various environmental conditions to which they will be exposed when used.
It should be noted, however, that they will always measure the "mean"
value of the temperature over their total winding or sensitive length.
Design of Elements
and Selection of Types
We produce three basic types of platinum resistance elements:
Thin
film elements have a sensitive platinum film deposited onto the ceramic former.
These types offer smaller dimensions and the possibility for higher nominal
resistances.
Wire
wound ceramic elements consist of a ceramic body having the heat
sensitive resistance wire encapsulated into longitudinal bores.
Wire
wound glass elements have the resistance winding solidly embedded
in a glass former making the elements suitable for extreme operating conditions.
For temperature detection and monitoring of stator windings in electrical
machines and generators, we offer slot type resistance thermometers.
A wide range of elements types are available offering different measuring
ranges, various shapes and sizes and numbers of resistance circuits carried
on the same body.
Assembly
Reliable
temperature measurements with platinum resistance elements require experience
in assembly procedures and selection materials. We offer a wide
range of ready to use resistance thermometers. For further information
on matters connected with precision temperature measurements such as the
general use of resistance thermometer assemblies, their operating principles,
construction, typical measuring circuits, installation, etc., please refer
to the Assemblies Catalog.
Reference
Tables
The reference tables conform to
the International Industrial Standard IEC 751 (identical with IEC 751,2:
1995-07, resp. DIN EN 60751: 1996-07) for the range:
-200 to +850C
Tolerances
The platinum
resistance elements listed here can be supplied according to tolerance
class B (acc. to IEC 751,2: 1995-07 resp. DIN EN 60751: 1996-07):
 in C = ± (0.3 C + 0.005 [t])
For applications calling for exceptional accuracy, tighter tolerances such as class A, 1/3 Class B, and 1/10 Class B are available.
Class A is defined as follows:
in
C = ± (0.15 C + 0.002 [t])
DWM can recommend versions with non-standard tolerances, e.g. at a given temperature or within a more restricted temperature range.
Response
Times
Platinum resistance elements are notable for exceptionally short response times. Values for response times in water and air are given in the tables on each product page.
Self-heating
Like all resistance elements through which a current flows, platinum resistance elements are slightly heated by the current. The magnitude of this "self-heating error" depends on the electrical energy input (N=I2 x R), the volume of heat dissipating and an apparatus constant "EK". The self heating constant for each resistance element when used in water or air is shown in the tables on each product page.
Long Term
Stability
Compared with other temperature sensors, Pt precision resistance
elements possess exceptional long term stability at the upper application
limit.
Supply Range
Standard types of elements are available in stock and at competitive
prices.
For special applications, non-standard versions are available with the
following options:
- Dimensions
- Nominal resistances
- Temperature coefficients
- Connection lead lengths
- Tolerances
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