Measuring Inputs And Additional Channels - Ahlborn ALMEMO 2490-2 Operating Instructions Manual

8. Connecting the transducers
double sealing lip to protect the socket unit against the effects of splashing wa-
ter. For any unused sockets protective stoppers are available.

8.2 Measuring inputs and additional channels

The ALMEMO 2490-1 has 1 input socket, version 2490-2 has 2 input sockets
®
(1); to these initially measuring channels M0 (and M1) are assigned. AL-
®
MEMO sensors can, however, if necessary, provide up to 4 channels. The ad-
ditional channels can be used in particular for humidity sensors with 4
measuring variables (temperature / humidity / dew point / mixture ratio) or for
function channels. Each sensor can if necessary be programmed with several
measuring ranges or scaling settings; and 2 or 3 sensors, if pin assignment so
permits, can be combined in a single connector (e.g. rH / NTC, mV / V, mA / V,
etc.). The additional measuring channel numbers per connector go up in steps
of 10 (e.g. the first sensor has channels M0, M10, M20, M30, the second
sensor has channels M1, M11, M21, M31 etc.).
Device-internal channels (2490-2 only)
A further innovation on this device is its four additional device-internal chan-
nels. The first of these M2 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. U-Bat, cold junction compensation, averages, etc.); (see Manual, Section
6.3.4). The reference channels are by default Mb1 = M1 and Mb2 = M0.
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 the function
channels on the sensor itself makes more sense.
On the measuring instrument this gives the following channel assignment :
sensor channels
4. chan. 30
3. chan. 20
2. chan. 10
1. chan.
00
M0
16 ALMEMO
2490-1
4. chan.
3. chan.
2. chan.
1. chan.
2490
®
sensor channels
Device internal channels
30 31 32
20 21 22
10 11 12
Difference M01-M00
00 01 02
M0 M1 M2
2490-2
A2 A1 DC