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Temperature probes type T/TW
If it is used for processes, however, which
are associated with the risk of product
deposits, it must be verified whether
or not product has accumulated on the
probe carrier. Deposits must be removed
using suitable means and methods.
5.8
Calibration of the T probe
5.8.1 General instructions
As mentioned before, the thermocouple
has been fused into the glass layer, thus
forming an integral part of the probe car-
rier. Calibrating the thermocouple sepa-
rately is not possible for this reason. It is
most practical to calibrate the T probe
with the probe carrier installed because
stable, reproducible temperature con-
ditions at the T probe are most conve-
niently achieved. Calibration outside the
reactor or pipeline is very problematic
because there is considerable heat dissi-
pation, which results in instable temper-
ature conditions at the thermocouple,
due to the shape and size of the probe
carriers. For calibration, the reactor or
the pipeline must be filled either with
product or with water. A steady tempera-
ture at the transmitter must be ensured
during calibration. For this reason, the
terminal box should be closed.
For calibrating tubular probes, the reac-
tor must be filled until the immersion
depth of the measuring location is at
least five times the tube diameter. When
calibrating inside a reactor, the agitator
must turn slowly in order to ensure an
even temperature distribution inside the
liquid.
For ring probes, the pipeline must be
fully filled. Ring probes may also be cali-
brated outside the pipeline due to their
compact dimensions. For this purpose,
the probe must then be immersed into a
suitable vessel. Caution! Do not immerse
the terminal box.
10
When calibrating outlet valves, the valve
cone must be sufficiently covered with
product so as to ensure a stable tem-
perature condition in the measuring
location. Furthermore, the agitator must
be slowly turned during calibration.
5.8.2 Calibrating the measuring
chain
In order to calibrate the entire measuring
chain including the sensor, transmitter
and display unit, immerse a calibrated
reference thermometer into the liquid
and compare its measured value (refer-
ence value) with the value measured by
the T probe (actual value). If it is neces-
sary to calibrate the T probe at different
temperatures, we recommend calibrat-
ing it in icy water at 0 °C and in boiling
water at 100 °C.
The result will be reliable information
concerning the accuracy of the entire
measuring chain and the actual tempera-
ture conditions in the subsequent pro-
duction process.
If an excessive, inadmissible measuring
deviation is detected during calibration,
the individual elements of the measuring
chain must be verified or calibrated.
5.8.3 Calibrating the sensor
Actually, it is not necessary to calibrate
the sensor (thermocouple) for technical
reasons because the sensor is not sub-
ject to ageing (refer to Sect. 5.7).
Temperature probes type T/TW
However, in some cases the sensor has
to be calibrated to comply with internal
or process-related requirements. The
Pfaudler T-Calibrator (part no. 256572-)
and the Smart Vision firmware must be
available in order to calibrate the ther-
mocouple. For more information and a
detailed description of the calibration
process, please refer to the Operating
Instructions of the T-Calibrator.
5.8.4 Calibrating the transmitter
In order to calibrate the transmitter, a
process calibrator is connected to the
transmitter input that serves to simulate
the thermocouple's characteristic. Then,
the voltage values of the characteristic
are entered one by one at the process
calibrator. In parallel, the actual values
of the transmitter (input and output sig-
nal) are compared to the programmed
values (values of the characteristic). The
values of the characteristic are indicated
in the test report that is attached to each
probe supplied. It is important to deac-
tivate the internal reference point of the
transmitter during calibration. Please
refer to the Operating Instructions of the
TH02-Ex unit for a description of how to
deactivate the reference point.
5.8.5 Calibrating the display unit
In order to calibrate the display unit,
an additional, calibrated display unit
is looped into the transmitter's output
circuit, and the two values displayed as
actual and programmed values must be
compared.
5.9
Explosion protection
The tubular and ring probes with an
integrated T probe have been approved
for use in potentially hazardous atmos-
pheres of zone 0 in accordance with the
EC type examination certificate No. PTB
03 ATEX 2132 X. For outlet valves with
an integrated T probe, an EC type exami-
nation certificate has been applied for.
© Pfaudler GmbH · OI 302-8 e
© Pfaudler GmbH 10
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