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SC Case description Intermediate result Final result
The measuring sensor is situated at a process frame in a produc-
tion facility and the measuring transducer in a control room inside
the production building which is not equipped with an external BLITZDUCTOR XT BLITZDUCTOR XT
1
lightning protection system. The measuring lines are routed BXT ML4 B... BXT ML4 B...
inside the building. This example corresponds to case d (Figure
8.2.14).
The surge threat to the Pt 100 measuring sensors and Pt 100
2 measuring transducer arises between signal core and earth. This BLITZDUCTOR XT BLITZDUCTOR XT
BXT ML4 BE
BXT ML4 BE
requires fine limitation of common-mode interference.
There are no special requirements to adjust the protective circuit
3 to the input circuit of the devices to be protected (Pt 100, Pt 100 No impact BLITZDUCTOR XT
BXT ML4 BE
measuring transducer).
The temperature measuring equipment to be protected is a system
supplied with direct current. The temperature-dependent measur- BLITZDUCTOR XT
4 No impact
ing voltage is also a d.c. voltage. Thus, no signal frequencies have BXT ML4 BE
to be considered.
The physical measuring principle of Pt 100 limits the operating I L of type BE = at least 0.75 kA
current of the supply circuit to 1 mA. The operating current of the BLITZDUCTOR XT
5 1 mA < 0.75 A ¨ ok
measuring signal is in the µA range due to the extremely high- µA < 0.75 A ¨ ok BXT ML4 BE
impedance measurement tap.
The maximum operating voltage in this system results from the
following consideration: According to IEC 60751, Pt 100 measur-
ing resistors are designed for a maximum temperature up to BLITZDUCTOR XT BLITZDUCTOR XT
6
850 °C. The respective resistance is 390 Ω. Considering the load- BXT ML4 ... 5V BXT ML4 BE 5
independent measuring current of 1 mA, a measuring voltage of
approx. 390 mV occurs.
BXT ML4 BE 5 has a nominal volt-
age of 5 V d.c. core ¨ earth, thus BLITZDUCTOR XT
7 The operating voltage of the system arises from core to core.
10 V d.c. core ¨ core, possible ¨ BXT ML4 BE 5
No impact on the measuring signal
When using the four-conductor circuit for measuring the tem-
perature with Pt 100, the influence of the cable resistance and
its temperature-related fluctuations on the measuring result is BLITZDUCTOR XT
8 No impact
completely eliminated. This also applies to the increase of the BXT ML4 BE 5
cable resistance by means of the decoupling impedances of
BLITZDUCTOR XT.
BLITZDUCTOR XT
BXT ML4 BE 5
The Pt 100 measuring transducer has an immunity to conducted
interference according to test level 2 as per IEC 61000-4-5
9 (EN 61000-4-5). The “let-through energy” related to the voltage "Let-through energy" according to BLITZDUCTOR XT
test level 1; "let-through energy"
BXT ML4 BE 5
protection level of the surge protective device must not exceed of the protective device is lower
test level 2 of IEC 61000-4-5 (EN 61000-4-5).
than the immunity of the terminal
device ¨ is ok
BLITZDUCTOR XT
10 One-stage surge protection is required BXT ML4 BE 5 BLITZDUCTOR XT
BXT ML4 BE 5
¨ combined arrester
BLITZDUCTOR XT
Result of the selection:
BXT ML4 BE 5
Table 8.2.3 Selection criteria for electrical temperature measuring equipment

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