8. Connecting the sensors / transducers
20
programmed by default as differential channel M1 – M0. This only applies, how-
ever, if there are two sensors with the same units and same decimal point posi-
tion connected at measuring points M0 and M1. The fourth (M32/M34, depend-
ing on type) is used temporarily for the purposes of averaging (see 12.2). How-
ever, all 4 channels can be programmed with any other function channels (e.g.
U-Bat, cold junction compensation, averages, volume flow, etc.); (see 13.10,
Manual Section 6.3.4).
The
advantage
of device-internal channels is that when using several sensors
for the same application these sensors do not have to be reprogrammed and
can be exchanged without losing the function channels. However, if the whole
application operates with just one sensor, then programming on the sensor itself
makes more sense.
This, depending on device type, gives the following channel assignments :
8.3
Potential separation
When organizing a properly functioning measuring setup it is very important to
ensure that no equalizing current can flow between sensors, power supply, and
peripherals. All points must therefore lie at the same potential and / or any une-
qual potentials must be electrically isolated.
The analog inputs are electrically isolated by means of photovoltaic relays; the
maximum potential difference permitted between them is 50 VDC or 60 VAC.
Sensors combined within one connector and sensors with their own power sup-
ply, however, are electrically interconnected and must therefore be operated in
