Vaisala HMP140 - Manual (Page 12)

HMP140A SERIES
Operating Manual
U175en-1.5
8 1999-12-08
3.6 Connection to an AC supply
The HMP140A transmitters can also be connected to an AC supply without an
external rectifier. However, when two or more transmitters are connected to
one 24 VAC transformer, a common loop is formed and there is an increased
risk of a short-circuit. To avoid this, always use separate floating supply for
each transmitter (see Figure 3.6 A). However, if several transmitters have to
share one transformer, always connect the phase (
∼
) to + connector in each
transmitter (see Figure 3.6 B).
HMP140 transmitter
HMP140 transmitter
Controller
shared
common line
HMP140 transmitter
HMP140 transmitter
Controller
s
u
pply vol
ta
g
e
s
ign
a
l out
put
sup
p
ly
volt
age
s
ig
n
al
ou
tp
u
t
B) COMMON LOOP FORMED - NOT RECOMMENDED!
A) NO COMMON LOOP FORMED - RECOMMENDED
s
uppl
y
v
o
lt
age
si
gnal
out
put
su
p
p
ly vo
lt
a
g
e
si
gna
l out
put
Figure 3.6 Connecting the transmitters to a 24 VAC supply