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:
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.
The 2 inputs on version 2470-2 are electrically isolated by means of photovol-
18 ALMEMO 2470
M0
00
10
20
30
1. Chann.
2. Chann.
3. Chann.
4. Chann.
DC
Sensor channels
2470-1S
M0 M1 M4
00
10
20
30
01
11
21
31
A2 A1 DC
04
14
24
34
Device-internal channels
Difference M01-M00
Sensor channels
2470-2/2S
1. Chann.
2. Chann.
3. Chann.
4. Chann.
M1
M0
Data cable
AC
DC
DC
DC
ADC
uC
U-
U+
Sensor
Power supply
10..30V=
230V≈
