IFM Electronic AC2520 Montageanleitung Seite 9

Connection of a 4-wire Pt100 element to the AS-i module
Analogue modul
Pin 1: S +
Pin 2: AI +
Pin 3: S -
Pin 4: AI -
Pin 5: screen (functional earth)
4-wire Pt100 sensors supply more exact results than 2-wire sensors
provided that the wire resistance is the same.
The changeover between 2- and 4-wire sensors is made via the para-
meter bit P3.
Important notes regarding Pt100 measurements:
In the Pt100 measurement principle, very low currents flow in the mea-
suring electronics. It must be ensured that additional resistance (cables,
contact and transition resistance, loose contacts, etc.) is avoided in the
measuring circuit.
Only this way is a precise measurement, for which these modules are
designed, possible.
In detail:
A 4-wire measurement always has to be preferred over a 2-wire mea-
surement. In 2-wire measurement all transition and connection resi-
stances add up and may massively falsify the measurement result.
Therefore a 2-wire measurement is not recommended!
High-quality plugs should be used for the AS-i AC2520 Pt100 module.
Prewired and potted plugs with gold-plated contacts should be prefer-
red.
4-wire Pt100
Pt100
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