Datasheet

7
PRTDs sold by TDI are manufactured by hand, to very high
standards, under the most rigorous of Quality Control Conditions.
A TDI Quality Assurance Manual is available to any prospective
customer upon request. All materials used in their manufacture are
traceable to Quality Control assurance by the various suppliers. All
production is carried out under clean conditions with much of the
production assembled with the use of microscopes. The units are
visually checked for quality at least 4 times during production. In a
final check all units are checked against a known standard which
has been calibrated in the Calibration Laboratory of Isotech, whose
U.K.A.S. accreditation enables us to have a close quality control.
During the manufacture, all units are aged at temperatures higher
than those specified by the various standard bodies. This treatment
gives our units a high degree of stability at normal working
temperature. During the final grading, units are selected to higher
tolerances than those stipulated. Alpha value of sensing wire is
better than 0.003850 +/-0.000006. This is better than the Class B
requirement of +/-0.000012.
Vibration
When correctly supported, units will withstand a minimum vibration
level of 30g over the frequency range 10hz to 1Khz. Units from
normal production have been subjected to many varied ranges of
vibration, and we have in-house ability to test to a Customer’s
needs should they have any special requirement.
Stability
Detectors typically conform to BSEN Stability figures. Drift of less
than ±0.05% of its initial value after ten thermal cycles from 0ºC to
600ºC and from -200ºC to 0ºC. Stability is a compromise between
vibration performance and there are various options available.
Self Heating
Less than 0.3ºC with 10mW dissipation when tested in a stirred ice bath.
Detector Specification
Normally 3 types of alpha value platinum are available for use in the
construction of our PRTDs.
1 Designated P - (White Cap)
Specification to:
A BS EN 60751 1996 B DIN 43760 1980 C IEC 751 1995
(The European Standard EN 60751:1995 has the status of the BS EN
60751:1996 British Standard)
Resistance at 0ºC 100 ohms
Alpha Value - 0.003850ºC
-1
Other Tolerances
As well as the standard tolerances, TDI produce closer tolerance
versions of their products:
Typically: ±0.05% (1/2DIN B)
±0.03% (1/3 DIN B)
±0.02% (1/5 DIN B)
±0.01% (1/10 DIN B)
being the interchangeability at 0ºC.
As the detector is used further away from 0ºC these errors can be
expected to increase in accordance with an alpha uncertainty of
±3ppm.
If further requirements pertain, then Calibration in our sister
company Isotech’s U.K.A.S. Laboratory is essential.
NB Great care in assembly is required to maintain the accuracy
provided by the close tolerance detector.
2 Designated A - (Pink cap)
Specification to:
A JIS C1604 - 1981 (Japanese Industrial Standard)
B US Standard Curve
Resistance at 0ºC 100 ohms or 50 ohms.
Alpha Value - 0.003916ºC
-1
Tolerance at 0ºC for
A JIS C1604 1981
±0.15ºC
±0.2ºC
±0.5ºC
B US Standard ±0.1 ohms
Variations as required under various SAMA Standard can be made
to order with variations of Ro.
3 Designated S - (Blue Cap)
Originally specified for British Aircraft Industry.
Specification to BS 2G 148
Resistance at 0ºC = 130 ohms
Alpha Tolerance - 0.003900ºC
-1
Tolerance at 0ºC - ±0.1% or Ro.
Variations of Ro are available on request.
Thermal response time
BS EN 60751:1996 & IEC 751: 1995
Require that the response time for a 50% change (~0.5) in resistance
to a step temperature change be recorded. The normal 63.2% value
is not recommended. However it is the accepted figure. Hence the
table below gives the 63.2% figure. The 50% figure may be
obtained by reducing the times given by approximately 10%. 90%
response times can be obtained by multiplying the the times given
by a factor of 3. To obtain the time constants at other flow rates and
for other liquids and gases, the times may be multiplied by the
inverse of the ratio masses of fluids per second passing the
element.
Ceramic diameter (mm) 4.5 3.2 2.8 2.4 2.0 1.6 1.5 1.2 0.9
Typical time (secs) 0.7 0.4 0.4 0.3 0.25 0.15 0.1 0.08 0.03
to 63% of final value,
50% step, water flowing at 1m/s.
Hermetically sealed units
For optimum stability, air should be allowed to circulate around the
platinum coil. For this reason our detectors are not Hermetically
sealed. Care must therefore be taken to prevent the ingress of
moisture or gases from contaminating the detector by enclosing it
in a suitable sheath. However applications have arisen where
detectors have to be totally immersed; or to operate in conditions
of high humidity. For special cases units can be hermetically sealed.
These units are made to order only.
PRTD Standards
For producing working standards to the International Temperature
Scale of 1990 (ITS-90) an alpha Value of at least 0.003925 is required.
TDI produce a 25.5 ohm detector which when correctly assembled
will meet the ITS-90 requirements.
A full working standard sensor assembly is produced by our sister
company Isothermal Technology Ltd. For full details ask for model 909.