Potential Separation - Ahlborn ALMEMO 2470-1S Operating Instruction

8. Connecting sensors / transducers
M24, M34. On the 2470-1SRH with its integrated sensors these are used for
the channels temperature, humidity, dew point, and atmospheric pressure.
On the other variants M4 is programmed by default as differential channel M1
– M0. This only applies, however, if there are two sensors with the same units
and same decimal point position connected at measuring points M0 and M1.
However, all 4 channels can be programmed with any other function channels
(e.g. battery voltage, atmospheric pressure, cold junction compensation, aver-
ages, etc.) (see Manual, 6.3.4)
The reference channels are by default Mb1 = M1 and Mb2 = M0.
Advantage of device-internal channels : Several sensors being used for the
same application do not have to be reprogrammed and can be freely ex-
changed without losing their function channel assignment. However, if the
whole application operates with just one sensor, then programming the func-
tion channels on the sensor itself makes more sense.
On the measuring instrument this gives the following channel assignment:
Sensor channels
30
4. Chann.
20
3. Chann.
2. Chann. 10
1. Chann.
00
M0

8.3 Potential separation

When organizing a properly functioning measuring setup it is very important to
ensure that no equalizing current flow between sensors, power supply, and
peripherals. All points must therefore lie at the same potential and / or any un-
equal potentials that do exist must be electrically isolated.
Sensor
M1
M0
The 2 inputs on version 2470-2 are electrically isolated by means of photovol-
18 ALMEMO 2470
2470-1S
4. Chann.
3. Chann.
2. Chann.
1. Chann.
DC
U+
ADC
U-
Sensor channels
Device-internal channels
30 31 34
20 21 24
10 11 14
00 01 04
M0 M1 M4
uC
Power supply
2470-2/2S
Difference M01-M00
A2 A1 DC
Data cable
DC
AC
230V≈
DC
DC
10..30V=