IMC CANSAS - Page 372

372 Properties of the Modules
imc CANSAS Users Manual - Doc. Version 1.9 - 05.12.2014© 2014 imc Meßsysteme GmbH
All three modules of this family are based on a scanner concept with block isolation, in which a
multiplexer is combined with an isolated measuring amplifier. In the SCIxx group, the switching matrix is
realized with optical relays, which offers extended isolation properties compared to the SC16 which has
electronic switches. What both groups have in common is that the inputs are provided with differential
properties by a measuring amplifier isolated block-to-block, which adjusts itself to the respective
common mode voltage of the connected source. This adjustment of the voltage entails reverse-charging
of the capacitors present and thus a short-term burden on the signal source. If the signal voltage is
unaffected by such factors (e.g. in the case of thermocouples, batteries, and Pt100-units fed from the
SCxx- module), there is practically no compromising of the measurement in any typical applications, since
the measurement system automatically compensates for the feedback effect. The maximum allowed
source impedance (refer to the technical specs) which may not be exceeded is so high that it doesn't
usually present any limitations.
Due to this property, however, the modules belonging to this family are not suitable for signal sources
which respond to these dynamic feedback effects. This can apply to active sensors or calibrators, for
instance, whose output level is low-frequency filtered or which is not able to correct quickly enough for
the dynamic load fluctuations.
Connection
The choices for signals to connect include voltage, current, or any DIN-thermocouples or Pt100s. The
"Opto"-modules SCI8 and SCI16 enable direct connection of signals up to ±60 V. SC16, by contrast
supports input ranges of ±100 mV to ±10 V directly and supports the extended input ranges up to ±60 V
by means of a special divider connector (ACC/DSUB-UD4).
The interconnections used are DSUB-15 terminals. One connector serves four signals.
Each channel can be connected individually which means it's possible to connect a voltage, a
temperature and a current all via on terminal. This can result in certain limitations if, for instance, a
current measurement is carried out with a shunt connector and a temperature measurement with a
thermocouple. Since these measurement types require a dedicated connector, only one measurement
type can be performed per DSUB.
In principle, it's possible to carry out both a voltage measurement and a thermocouple measurement
using the same thermo-connector. Likewise, a Pt100 measurement can be carried out using just a
standard connector, although doing this would prevent the convenient four-wire connection scheme
from being used.
To avoid crosstalk, which is typical for scanner systems, it is recommended to short circuit the inputs of
the channel, which are not in use.