Potential Separation - Ahlborn ALMEMO 710 Operating Instructions Manual

8.5 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 measuring points must therefore either be insulated (e.g. by air
spacing) or lie at the same potential - and any unequal potentials that do exist
must be electrically isolated.
U+
Sensors
M2
M1
M0
electr. isolated
U-
The 10 analog inputs on this device are electrically isolated from one another
by means of photovoltaic relays. A new feature is the additional separation of
the measuring inputs from the CPU and power supply. However, for some ana-
log sensors this electrical isolation may have to be disabled again by means of
relay S (see above) or a wire jumper; some inputs would otherwise be left with-
out reference potential. The first time any such sensor is connected this relay is
set automatically by means of element flag 5 'ISO OFF'.(see Manual 6.10.3).
However, with certain connectors (especially divider connectors without power
supply) element flag 5 should be checked and if necessary corrected. Between
all inputs and outputs (even those analog output cables not electrically iso-
lated) the maximum potential difference permitted is 50 V. The voltage at the
measuring inputs themselves (between B, C, D, and A) must not exceed 12 V.
However, some components are not electrically isolated, namely all sensors
connected to the common internal power supply ±U (including all D6 and D7
sensors) and sensors combined within one connector. No such problems af-
fect sensors without any conductive connection (D6). For D7 sensors (in par-
ticular electrical measuring connectors, conductivity probes) an adapter cable
ZAD700-GT is available; this provides electrical isolation for the power supply
and data lines. Non-insulated sensors can be sufficiently protected by electri-
cally isolating the power supply (battery, mains adapter, or connecting cable
with DC/DC converter).
Data and trigger cables are also insulated by means of optocouplers.
DC
ADC
B
A
S
DC
uC
ALMEMO
Potential separation
Data cable
DC
AC
Power supply
230V≈
DC
DC
10..30V=
® 710 21