13
MAIN UNIT
3
CONNECTIONS
3.4
Sensor Connection Examples
Transducers can supply signals of differing types. They are usually "single
ended" or "differential" (ratiometric). Below are some examples of how they
can be connected. Note that combinations are always possible.
It is also always good practise to plan connections and to make a schematic
diagram before actually doing them.
3.4.1
Connecting 20mA current loops
Currents are usually process type signals: 0-20mA or 4-20mA.
These loops can be connected in more ways than one.
It cannot be stressed enough that it is necessary to have a diagram of the
system from which these signals emanate in order to connect multiple
signals correctly.
Remember that the 51
Ω
shunt resistor has to be connected to the input
circuitry by putting the Dip-switch in position "current". See illustrations
below.
1) Connecting current loops with common grounding :
One connection to
the common ground
potential is enough.
Two would have
created a ground
loop that may cause
problems in the
form of electrical
interference.
"Other instruments" may also be connected in the current return path if it is
absolutely certain that the total voltage drop across them is well within max
common mode range.
