VEGA Z728 Zener barriers - Manual (Page 22)

22
Zener barriers - operating instructions
Application examples
Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany
Pepperl+Fuchs Group • Tel.: Germany +49 621 776-0 • USA +1 330 4253555 • Singapore +65 67799091 • Internet http://www.pepperl-fuchs.com
Da
te of issu
e
05/2
3
/03
LED display
The circuit shown above does not require a current limiting
resistor, since the Z728.CL limits the current electronically to a
maximum of 40 mA. At a supply voltage of 18 V … 27 V a
current of 40 mA flows in the intrinsically safe circuit. This current reduces at lower nominal supply voltages. To special
order, the Z728.CL can be supplied with lower current-limiting
values. The system is approved for [EEx ia] IIC. The Z828.CL
is also suitable for negative polarities.
Smoke and fire alarms
The simplest and most cost-effective solution is shown in the
illustration above. With a 24 V nominal supply voltage, there is
an off-state current of approx. 4 mA. When the detector
responds, the current increases to approx. 25 mA or greater. The current applied to the detector is sufficient to operate the
LED display with sufficient brightness. The system is approved
for [EEx ia] IIC.
The system shown above is comparable to the Z728 and is
also relatively inexpensive. The Z787 is a 2-channel device. In this application the intrinsically safe circuit is quasi ground-free.
The system is approved for [EEx ia] IIC.
Hazardous area Safe area
Z728.CL
x3
1
2
8
7
CL
Hazardous area Safe area
Output
I
Z728
x3
CL
1
2
8
7
Hazardous area Safe area
Output
I
Z787
x3
x3
1
4
3
2
8
5
6
7