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9.6.4
Conductor Preparation
The ends of the conductors to be fitted into the power plug, must be properly terminated with suitable ferules
(bootlace or flat-blade). The supplied power plug will accept terminations with a cross sectional area between
2
2.
0.2mm
and 2.5mm
It is not advisable to simply strip the conductors and place the un-terminated ends into the power plug, as this
is likely to fail over time.
Using striped and solder tinned conductor ends is also strongly discouraged since solder will 'cold-creeps and
compresses over time resulting in loose connections.
Connection to the barrier terminal connection strip is most reliable when using fork or ring type crimp terminals.
The barrier connector's cable clamp can accommodate conductors with a cross sectional range of 0.33mm
2
3.3mm
. Ring / fork terminals should have a hole / slot size greater than 3.7mm to allow the terminal screw to
pass through them freely.
9.6.5
Installation Cable Choice
For correct and reliable operation, electrical connections between the D-Guard
system must only be made using appropriate cable. The choice of cable will depend on application and general
adherence to the wiring regulations appropriate for the installation.
The presence of electrical noise in an installation can cause instability of the instrument readings if not
considered and removed by proper wiring methods.
Instability of this type generally shows as the measured gas value changing fairly rapidly in a random way.
Electrical noise may coincide with a piece of equipment (e.g. variable speed drive) switching on, off or as its
speed is controlled.
The size of the apparent changes in gas reading due to electrical noise could be sufficiently large to cause the
detector to enter an alarm state, especially for instruments with low alarm ranges such as 1ppm or less.
With proper cable shielding, noise can be dramatically reduced or eliminated, allowing the response from the
detector to properly represent the ambient gas conditions. The normal detector response is steady with only
small, slow variations in readings. If there are no background levels of gas present, then the readings should be
stable at or near zero with no significant variations.
The actual configuration of the shielding will depend upon the specific application, but as a rule, the cable shield
should be connected to earth (system ground reference point) at either the detector or the controller, but not
at both. In most typical applications, the shield will be connected to an appropriate ground point at the
controller end.
2
The D-Guard
detector has provision for connecting the cable shield using the middle screw terminal on the
terminal board barrier terminal connector. This connection point is electrically connected to the detector
enclosure which has conductive elements embedded within the plastic material.
The electrical conductivity of the enclosure is low and may under certain mounting conditions
contribute to the creation of noise loops if the cable screen is connected at the controller side of the
installation and also to the barrier terminal middle shield terminal. This may arise if the detector is
mounted on a metal plate which is also connected to the system ground.
If connecting the screen to both the controller side and the shield terminal of the detector, the
detector enclosure may need to be isolated from system ground.
Typical suitable cable types for installing D-Guard
twisted pair data cable such as Belden type 9829.
2
would be:- Type 2S (e.g. Olex MCFR58AA004) OR twin
22
D-Guard
2
2
detector and the rest of the
2
to
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