PCD0
Electrical installation
Page 120
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SAIA-Burgess Controls Ltd.
(HB_PCD0 26 766_E2.DOC)
26/766 E2
6.6
Connecting signal sources to analog modules
Voltage inputs
The 4 analog inputs are non-floating differential inputs. The voltage
potentials of the positive and negative signal poles should not exceed
the acceptable common-mode range (-12.1 ... + 12.8 V in relation to
AGND). Signals in excess of these limits would be clipped by the
following amplifiers. The result would be a corrupted measuring value.
The analog input potentials are isolated from the supply (+24 V, 0 V)
and from PE.
Observe the following when connecting signal sources to analog
inputs:
a) Floating signal sources:
If you connect a completely potential-free signal source to AIx+ and
AIx- only, high-resistance resistors in the module ensure that the pole
potentials are drawn to approximately the middle of the range.
However, since the potential coupling is only very high-resistance (to
prevent corruption of measured data) and thus very soft, the typically
occurring ripple voltages can result in a strong fluctuation of the pole
potentials and even exceed the common-mode range. Strongly
fluctuating or completely corrupted measured values are an indication
of this problem. To prevent this, fix the pole potentials by adding an
external potential connection to AGND.
b) Non-floating signal sources:
If you connect several non-floating signal sources to the various
analog inputs of the module, add a potential connection to AGND to
avoid freely floating signal potentials. Normally connection of a single
signal source potential with AGND is sufficient. If you use non-floating
signal sources make sure that the respective pole potentials are within
the common-mode range. If the pole potentials of two signal sources
are very different (example: 1
st
signal source supplies voltages related
to 0 V external, the 2
nd
signal source supplies voltages related to +24
V external), NEVER connect them to the same analog input module!
If you have open voltage inputs (differential input) the digital value
07FF hex is transferred.
