Vaisala GMM20W - Manual (Page 3)

GMM20W CO
2
module
Sensor Systems Division U300en-1.1
1997-07-22
POWER SUPPLY REQUIREMENTS
The GMM20W module is designed to
operate from a nominal 24 VAC/VDC
supply. The power supply should main-
tain the voltage between 18...30 VDC or
20...26 VAC for all load conditions and
all mains voltages. The power input in-
cludes a halfwave rectifier. To avoid
current peaks, it is recommended to use
a DC supply. The average transmitter
current consumption is 85 mA
maximum but peak currents of 170 mA
may occur during normal operation.
CONNECTION TO AN AC SUPPLY
The GMM20W module can also be
connected to a 24 VAC supply without
an external rectifier. However, when
more than one module 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 module (see Figure 4A). However,
if several modules have to share one
transformer, the phase (
∼
) must always
be connected to + connector in each
module (see Figure 4B).
A) NO COMMON LOOP FORMED - RECOMMENDED
24 VAC
24 VAC
24 VAC
B) COMMON LOOP FORMED - NOT RECOMMENDED!
GMM20W module
Controller
shared
common
line
GMM20W module
GMM20W module
GMM20W module
Controller
supply
voltage signal
output
supply
voltage signal
output
supply
voltage
supply
voltage
signal
output
signal
output
Figure 4 AC connections