Siemens 7MB2335, Operating Instructions Manual, Page: 21 / 168

Installation Guidelines
2-7
Operating instructions ULTRAMAT 23 gas analyzer
C79000-B5276-C216-03
2.5.2 Connection of Signal Cables
RC elements must be connected according to Fig. 2-2 as a measure to
suppress the generation of sparks across the relay contacts (e.g. limit
relays). Note that the RC element results in a drop-out delay for an
inductive component (e.g. solenoid valve). The RC element should
therefore be dimensioned according to the following rule-of-thumb:
R = R
L
/2; C = 4L/R
2
L
.
The following are usually sufficient: R = 100
Ω
and C = 200 nF.
Additionally make sure that you only use a non-polarized capacitor C.
When using direct current, it is possible to fit a spark suppression diode
instead of the RC element.
Connection side
24 V
R
C
Device side
Solenoid valve
When using direct current, a spark suppression diode
can be used as an alternative to the RC element.
Fig. 2-2 Measure to suppress sparks on a relay contact
The reference ground of the analog inputs is the housing potential.
The analog outputs are floating, but have a common negative pole.
The input/output cables must be connected to the corresponding
trapezoidal plug (SUB-D plug) according to the pin assignment
diagrams (see Chapter 3, Technical Description, pages 3-23 and 3-24).
The conductor cross-section should be
≥
0.5 mm
2
. The interface cable
must not be longer than 500 m.
Notice
The cables (apart from the mains cable) must be screened, and their
screen must be screen connected at both ends to ground.
The 24 V/1A power supply must be a power-limited safety extra-low
voltage with safe electrical isolation (SELV).