6.ELECTRICAL SYSTEM DESIGN FOR INSTALLATION IN HAZARDOUS AREAS USING ZENER BARRIERS
the galvanic isolator on and off, or by a mechanically activated switch on the hazardous area side of the isolator.
If the beacon is controlled by a switch in the positive supply, or the power supply is being turned on and off, only a single channel Zener barrier is required as shown in Fig 3. This circuit may also be used if the beacon is being controlled by a mechanically activated switch on the hazardous area side of the barrier. The power supply voltage should be between 20V and the maximum working voltage of the barrier. The circuit will continue to work at lower voltages, but the beacon light output level will be reduced.
If the beacon is being operated from a lower voltage power supply of say 12V or less, then a 15V 100 ohm barrier can be used which will improve the beacon light output levels at lower voltages.
Hazardous Area | Safe Area | |
Klaxon | Galvanic | |
Beacon | Isolator | |
+ | + | |
- | ||
- | ||
|
On / Off | + | |
Power | ||
| ||
| Supply | |
| 0V |
Hazardous Area | Safe Area |
|
Syrex | 28V | 1.2W |
Beacon | ||
| Positive | |
+ | Barrier | + |
| ||
|
| |
- |
| On/Off |
| Power | |
|
| |
|
| Supply |
|
| 0V |
Fig 3 Using a single channel barrier.
If the beacon control switch is in the negative wire and the power supply 0V is earthed, the circuit shown in Fig 4 may be used. For simplicity the two barriers may be combined into one package. The power supply voltage should be between 21V and the maximum working voltage of the 28V barrier. The circuit will continue to work at lower voltages, but the beacon brilliance will be reduced.
Fig 5 Basic circuit for use with a galvanic isolator.
The control arrangement will vary depending upon the isolator chosen. The galvanic isolator must be able to supply an output of 30mA at about 16V.
10. CABLE PARAMETERS
The maximum permitted cable parameters are as specified on the certificate of the Zener barrier or galvanic isolator that has been selected for the installation. Normally the limits are not restrictive, but care should be taken not to exceed a capacitive limit of 83nF for IIC installations when very long cables are used.
11. BEACON FLASH RATE
The Syrex
The flash rate is selected by the position of the pin header next to the input terminal block (see fig 1).
Hazardous Area
Syrex
Beacon
+
-
Safe Area
| 28V 1.2W |
| Positive |
Barrier | + |
| Power |
| Supply |
Diode Return |
|
Barrier | On/Off |
| |
| 0V |
12. MAINTENANCE
The beacon should be regularly inspected to ensure that it has not been damaged. Frequency of inspection depends upon environmental conditions, but initially we recommend that this should be done annually.
No attempt should be made to repair a faulty Syrex
13. GUARANTEE
Beacons which fail within the guarantee period should be returned to Klaxon Signals Ltd. or our local agent. It is helpful if a brief description of the fault symptoms is provided.
Fig 4 Single stage alarm using two channel barrier.
7. ELECTRICAL SYSTEM DESIGN FOR INSTALLATION IN HAZARDOUS AREAS USING GALVANIC ISOLATORS.
Galvanic isolators do not require a high integrity earth connection. For small systems where a high integrity earth is not already available, the use of galvanic isolators often reduces the overall installation cost and simplifies design.
The Syrex
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Klaxon Signals Ltd. Wrigley Street, Oldham, Lancashire UK OL4 1HW | sales@klaxonsignals.com | Tel: +44 (0)161 287 5555 | ||
Document No. Klaxon Syrex | Issue: A | Sheet 3 of 3 | www.klaxonsignals.com | Fax: +44 (0)161 287 5511 |
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