1592038710 Gas Leak Detector Modbus GB 01.12.2016
GDS41M-GDS66M-GDI41M-GDI66M 7/28
3.2 PLACEMENT
Sensors must be located within the appropriate wire lengths from the central control unit (if used).
In all cases the sensor supplied is designed for maximum sensitivity to a particular gas.
However, in certain circumstances false alarms may be caused by the occasional presence of
sufficiently high concentrations of other gaseous impurities.
Examples of situations where such abnormalities may arise include the following:
Plant room maintenance activity involving solvent or paint fumes or refrigerant leaks.
Accidental gas migration in fruit ripening/storage facilities (bananas - ethylene, apples -
carbon dioxide).
Heavy localized exhaust fumes (carbon monoxide, dioxide, propane) from engine-driven
forklifts in confined spaces or close to sensors.
Dixell recommends setting the alarm delay to minimize false alarms.
Note:
The Gas Sensor should be installed plumb and level and securely fastened to a rigid
mounting surface.
3.2.1
MACHINERY ROOMS
There is no absolute rule in determining the number of sensors and their locations. However, a
number of simple guidelines will help to make a decision. Sensors monitor a point as opposed to
an area. If the gas leak doesn
’t reach the sensor then no alarm will be triggered. Therefore, it is
extremely important to carefully select the sensor location. Also consider ease of access for
maintenance.
The size and nature of the site will help to decide which method is the most appropriate to use.
Locations requiring the most protection in a machinery or plant room would be around
compressors, pressurized storage vessels, refrigerant cylinders or storage rooms or pipelines.
The most common leak sources are valves, gauges, flanges, joints (brazed or mechanical), filling
or draining connections, etc.
When
mechanical or natural ventilation
is present, mount a sensor in the airflow.
In machinery rooms where there is
no discernable or strong airflow
then options are:
o
Point Detection
, where sensors are located as near as possible to the most
likely sources of leakage, such as the compressor, expansion valves,
mechanical joints or cable duct trenches.
o
Perimeter Detection
, where sensors completely surround the area or
equipment.
Sensors should be positioned just far enough back from any high-pressure parts to allow gas
clouds to form and be detected. Otherwise, a gas leak might pass by in a high-speed jet and not
be detected by the sensor.
Make sure that pits, stairwells and trenches are monitored since they may fill with stagnant
pockets of gas.
If a pressure relief vent (PRV) pipe is fitted to the system, it may be a requirement to mount a
sensor to monitor this vent pipe. It could be positioned about 2 m (6 feet) above the PRV to allow
gas clouds to form.
For racks or chillers pre-fitted with refrigerant sensors, these should be mounted so as to monitor
the compressors. If extract ducts are fitted the airflow in the duct may be monitored.
