Dwyer DPM - Manual (Page 14)

Particulate Monitoring Systems
Installation & Operating Manual
Document No. 210-1003-M Page 7 ©2007
4. Particulate Sensor Installation
4.1 Location
The following factors should be considered when determining the sensor location:
ƒ Area Classification
ƒ Flow conditions
ƒ Electrical (Faraday) shielding
ƒ Atmospheric shielding (in the case of ducts and stacks open to atmosphere)
ƒ Access for installation and service
SENSOR LOCATION
• Before installing the sensor, confirm area classification requirements. Do
not install any device that is not tagged suitable for the required area
classification.
• Before installing the particulate sensor, confirm ambient temperature,
process temperature and process pressure requirements. Do not install any
device that is not tagged as suitable for the required temperatures or
pressures. Confirm compatibility of wetted and non-wetted materials.
• For hazardous areas, a maximum ambient temperature of the particulate
sensor enclosure must not be exceeded. Refer to the Temperature
Considerations section for full details.
It is essential for the pipe/duct to provide an electrical (Faraday) shield for the sensor. It is therefore
required that the pipe, duct or stack is metal and earth grounded (small inline tubing sensors provide
their own section of metal pipe which also must be grounded). Consult the factory when insertion
probe style sensors are to be installed in non-conductive pipes, ducts such as plastic or fiberglass.
The particulate sensor must be installed in a position where the flow is reasonably laminar and the
particulate is evenly distributed. The ideal position is where the pipe/duct is straight and free of items
such as valves, dampers or other flow obstructions for a length of 4 diameters or longer. Horizontal or
vertical sections are acceptable. For basic flow/no flow detection it is not necessary to select a
location with a long straight section if access has to be sacrificed dramatically. For trending and
measurement the need for a straight section and laminar flow increases. The particulate sensor should
be positioned with approximately two thirds of the straight section upstream of the sensor and one
third downstream. The particulate sensor should be located in the center of the pipe/duct. If the
pipe/ducting is square it should be located in the center of one of the sides. In either case, be sure the
position is such that the tip of the sensor reaches the midpoint or beyond. Always use good
engineering sense and be sure the sensor will interact with a reasonable representation of the flow.
For emissions detection applications such as baghouses or cartridge collectors, good locations are
generally found upstream of the blower. The particulate sensor can be located downstream of the
blower but not too close to the stack outlet. There must be sufficient duct downstream of the sensor to
provide adequate electrical and atmospheric shielding. The sensor should be located upstream of any
sampling ports by at least two feet. It is not necessary that the sensor be in the same section of the
duct/stack as the sampling ports. Particulate sampling ports require fully-developed laminar flow and
longer straight sections.