Vaisala GMD20 - Manual (Page 3)

POWER SUPPLY REQUIREMENTS
The GMD20 transmitter is designed to operate from a nominal 24 VAC/VDC supply. The
power supply should maintain the voltage between 18...30 VDC or 20...26 VAC for all
load conditions and all mains voltages. The power input includes a halfwave rectifier. To
avoid current peaks, it is recommended to use a DC supply. The average transmitter cur-
rent consumption is 85 mA maximum but peak currents of 170 mA may occur during
normal operation.
CONNECTION TO A 24 VAC SUPPLY
The GMD20 transmitters 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 3A).
However, if several transmitters have to share one transformer, the phase (
∼ ) must always
be connected to + connector in each transmitter (see Figure 3B).
A)
B)
Figure 3 AC connections
24V OUT
GND
24V OUT
GND
CONTROLLER
GM20
Signal
output
Signal
output
Supply
voltage
Supply
voltage
24VAC
24VAC
GM20
24V OUT
GND
24V OUT
GND
Signal
output
Signal
output
Supply
voltage
Supply
voltage
SHARED
COMMON
LINE
GM20
GM20
CONTROLLER
24VAC
CO
2
transmitter GMD20 and GMD20D M210292en-A
3