General Information; Avoiding Damages To Peripheral Devices Contents; Temperature Probe Type T; Measuring Principle - Pfaudler TW Series Operating Instructions Manual

Temperature probes type T/TW
4.3

General information

During a spark test, inflammable sparks
may occur at the pores in the form of an
electric arc. Therefore, spark testing may
only be carried out outside of potentially
explosive atmospheres.
4.4 Avoiding damages to
peripheral devices
When performing a spark test, please
note the following information; other-
wise, the components and/or the elec-
tronic transmitter may get damaged.
The measuring transducers for tem-
n
perature, glass monitoring, capacitive
sensors and other electronic/electric
components that have been attached
to the valve or the baffle must be dis-
connected prior to the spark test.
Suitable equipment must be employed
n
for the test (impulse voltage). We rec-
ommend using the GlaSparker
high-voltage tester
For glass lined measuring probes, the
n
max. test voltage must not exceed
7 kV.
The contact window around the meas-
n
uring probe site (e. g. P) must not be
tested.
In general, however, we recommend call-
ing our technical service for performing
the test.
4
5

Temperature probe type T

5.1

Measuring principle

The temperature probe Type T will also
be referred to as the T probe in the
present Operating Instructions.
As already mentioned, a thermocouple
serves as the sensor of the T probe. A
thermocouple consists of two electrical
conductors made of different materials
(wires) that are connected (in contact) to
each other at one end. The contact point
is the measuring location of the thermo-
couple. The two free wire ends constitute
the reference location of the thermocou-
ple. If the thermocouple is heated in the
measuring location, a thermal voltage is
present in the reference location. This
thermal voltage depends on the temper-
ature difference between the mea s uring
®
, our location and the reference location (tem-
perature gradient along the thermocou-
ple), and on the material combination
of the two metal wires. For temperature
measurements, the temperature of the
reference location must be kept con-
stant at 0 °C, or it must be precisely mea-
sured in order to perform an appropriate
adjustment in mV. To evaluate the ther-
mal voltage, the free wire ends of the
thermocouple (the reference location)
are connected to a suitable transmitter.
Standard EN 60584 defines the various
material combinations for the produc-
tion of thermocouples. These standard-
ized material combinations are referred
to as "thermocouple types" and marked
by different capital letters. One of them
is the letter "T".
Temperature probes type T/TW
m
The T probe is not identical to
thermocouple type T.
The standardized thermocouple types
are not suitable for the T probe for rea-
sons of glassing technology. The positive
branch of the T probe is made of a plati-
num-rhodium alloy (PtRh), the negative
branch is made of a gold-palladium-plati-
num alloy (AuPdPt). This material com-
bination is known as "pallaplat". Table 1
shows the values of the basic character-
istic of pallaplat. However, these values
may only serve as reference values. The
exact characteristic depends on the
manufacturing batch of the pallaplat.
For programming the transmitter (refer
to Section 5.3), the characteristic that
was determined for the specific pallaplat
batch after production will be used. The
values entered during programming will
be indicated in the test report that is
attached to each probe supplied.
Only the Pfaudler-approved pallaplat
compensating line (part no. 029034)
may be used as an extension for the
thermocouple.
© Pfaudler GmbH · OI 302-8 e
© Pfaudler GmbH 4