Measuring inputs , additional channels
8.4 Measuring inputs , additional channels
Measuring instrument ALMEMO
®
809 incorporates nine input sockets M0 to
M8 (1); to these, under the new channel numbering scheme, measuring chan-
nels M0.0 to M8.0 are initially assigned. Whereas standard sensors can if ne-
cessary provide up to four channels (M0.0 to M0.3, M1.0 to M1.3, etc.), D7
sensors can provide up to 10 (M0.0 to M0.9, M1.0 to M1.9, etc.). The additio-
nal channels can be used in particular for humidity sensors with numerous
measurable variables (temperature / humidity / dewpoint / mixture ratio) or for
function channels. Each sensor can if necessary be programmed with several
quantities or scaling settings; and two or three sensors, if pin assignment so al-
lows, can be combined in a single plug (e.g. RH / NTC, mV / V, mA / V, etc.).
This device does not incorporate any internal channels.
On the measuring instrument this gives the following channel assignment:
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.
The nine 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 wi-
thout reference potential. The first time any such sensor is connected this re-
lay is set automatically by means of element flag 5 '
ISO OFF
'. (see Man. 6.10.3)
However, with certain connectors (e.g. divider connectors without power sup-
ply) element flag 5 should be checked and if necessary corrected. Between all
inputs and outputs (even those analog output cables not electrically isolated)
the maximum potential difference permitted is 50 V. The voltage at the measu-
ALMEMO
®
809
19
M0 M1 M2 M3 M4
0.0
0.1
0.2
0.3
3.0
3.1
3.2
3.3
4.0
4.1
4.2
4.3
1.0
1.1
1.2
1.3
2.0
2.1
2.2
2.3
1. chann.
2. chann.
3. chann.
4. chann.
Sensor channels with
new channel numbering
5.0
5.1
5.2
5.3
6.0
6.1
6.2
6.3
7.0
7.1
7.2
7.3
8.0
8.1
8.2
8.3
M5 M6 M7 M8
V5/6 sensors
D7 sensors
4.4 5.4 6.4 7.4 8.4
4.9 5.9 6.9 7.9 8.9
5. chann.
10. chann.
...
...
...
...
...
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