IB IL TEMP 4/8 RTD ...
7079_en_05 PHOENIX CONTACT 25
20 General notes and recommenda-
tions for the signal/noise ratio
Optimizing the signal/noise ratio in RTD applications using
the IB IL TEMP 4/8 RTD terminal.
Background:
The terminal used has a high dynamic performance and can
quickly detect the smallest changes in resistance or temper-
ature. In practice, however,a Pt100 sensor in air immedi-
ately passes on even the smallest changes. Temperature
fluctuations due to air circulation are measured immediately
and are transmitted to the higher-level PLC.
Remedy:
High dynamics is not required for all applications. In order to
obtain more stable measured values, set the internal filter-
ing parameter to 32-sample filtering. Moreover, an addi-
tional application filter can improve the signal/noise ratio. As
far as noise levels are concerned, 2-wire operation is more
favorable than 3-wire operation.
The thermal system at the sensor can be slowed, if required.
This can be achieved, for example,by installing it on a body
with a high thermal storage capacity. This could be, for ex-
ample, a metal block of aluminum or steel. The signal/noise
ratio will be influenced positively.
Overview of the recommended measures for temperature measurements with minimized noise:
No. Sensor type Filter Connec-
tion
Remarks Other
1Pt100
Ni100
32 2/3 With regard to the signal/noise ration it
is much better to use 2-wire termina-
tion instead of 3-wire termination for
terminal operation.
Check the tolerances for each respec-
tive measuring task.
– Short circuit unused channels.
– Enlarge the sensor ground (con-
nect sensor ground, for example,
to a metal block).
– If required, use an additional ap-
plication filter.
2Pt1000
Ni1000
32 2 Check the tolerances for each respec-
tive measuring task.
3 Pt10000 32 2 Due to the high R
0
, a 2-wire connec-
tion is recommended, ideally with long
supply lines. In addition, when using a
2-wire connection, the signal/noise
ratio is more favorable.
(Example: In order to keep the influ-
ence of the cable resistance at a value
of< 0.1 K, the copper cable may be up
to 110 m long with a cross-section of
0.25 mm
2
.)
