MAN3041-1
23
12
Maximum loading of IS circuit
Because of the finite resistance of the safety barrier, there will be a limit to the current drain which can be
tolerated before the voltages on the circuit fall outside the specified limits for Orbis I.S. devices. The system
certification allows up to 20 Orbis IS detectors to be connected to a single barrier circuit with an end-of-line
resistor of not less than 1.8kΩ. However, it must be ensured that the voltage available at each detector is
above the minimum specified in the quiescent condition. It is also important to ensure that the alarm load
is suitable for the control and indicating equipment. The system certification also allows the use of remote
LED indicators. These may be connected to individual detectors or may use a connection common to two or
more detectors as shown in Figure 6.
13
Installation
It is important that the Orbis I.S. detectors be installed in such a way that all terminals and connections are
protected to at least IP20 when the detector is in the base. Special care must be taken with the rear of the
mounting base where live metal parts may be accessible. Flush mounting of the base on a flat surface will
provide the required degree of protection.
A conduit, Item No 201-0192 (part No 45681-204), is also acceptable for mounting I.S. bases together with
a range of deckhead mounting boxes. For more information, please refer the Ampac eCatalogue.
Note that the earth terminal in the base is provided for convenience where continuity of a cable sheath or
similar is required. It is not necessary for the correct operation of the detector nor is it provided as a
termination point for a safety earth.
14
Remote LED connection
A drive point is provided on each of the Orbis I.S. detectors for a remote LED indicator. For connection
details see Figure 5. The indicator must be a standard high-efficiency
red
LED and does not require a series
limiting resistor since current is limited by the detectors.
The system certification allows for the use of any LED indicator having a surface area between 20mm
2
and
10cm2 which covers all commonly used case styles from T1 (3mm) upwards but would exclude some
miniature and surface mounted types. Additional requirements of the certification are that the LED and its
terminations must be afforded a degree of protection of at least IP20 and must be segregated from other
circuits and conductors as defined in BS EN 60079- 14:2003. The MiniDisc Remote Indicator, part No
(53832-070) may be used with Orbis IS detectors.
15
MiniDisc Remote Indicator
The MiniDisc remote indicator is only 20mm high and 80mm in diameter. It comprises two parts, the base
which is installed onto a wall or soffit and the lid which is fitted to the base with a bayonet fitting. An anti-
tamper screw in the lid locks the unit together.
Two pairs of keyholes are provided
–
one for 50mm and the other for 60mm fixing centres. The MiniDisc
Remote Indicator is polarity sensitive. Connect positive line to Terminal B and negative line to Terminal C.
