Vaisala HMP240 - Manual (Page 18)

HMP240
User's Guide
M210300en
16
3.4.1 Connection to a 24 VAC supply
The HMP240 transmitter can also be connected to a 24 VAC supply without
an external rectifier. However, when more than one transmitter is 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 3.7 A). However, if several transmitters have to
share one transformer, the phase (
∼
) must always be connected to + connector
in each transmitter (see Figure Figure 3.7 B).
24 VAC
HMP243 transmitter
HMP243 transmitter
Controller
shared
common line
24 VAC
24 VAC
HMP243 transmitter
HMP243 transmitter
Controller
s
u
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B) COMMON LOOP FORMED - NOT RECOMMENDED!
A) NO COMMON LOOP FORMED - RECOMMENDED
Figure 3.7 Connecting the transmitters to a 24 VAC supply (valid
also for the HMP247 transmitter).