Dwyer PMT - Manual (Page 14)

Particulate Monitoring Systems
Installation & Operating Manual
Document No. 210-1015-F Page 8 ©2007
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.
Extreme vibration should be avoided.
_ ATMOSPHERIC AND ELECTRICAL SHIELDING OF SENSOR
• It is essential for the pipe/duct to provide an electrical (Faraday) shield for
the sensor. The pipe/duct or stack should be metal with a high quality earth
ground. Consult the factory for non-conductive pipes/ducts such as plastic
or fiberglass. (Small in-line sensors for small tubing provide their own
section of metal pipe, which also must be grounded).
• When the sensor is placed in a stack/duct choose a location away from
atmosphere so wind driven atmospheric particulate or rain does not flow
over the sensor and so external electrical noise cannot affect operation.
• Do not place the sensor where the pipe/duct is corroded or cracked which
may allow water droplets to create signals as they flow by.
4.2 Mounting
The following types of process mounts are available for the standard probe style sensors:
NPT, Quick-Clamp and ANSI flange.
Inline sensors for small tubing are supplied with swage lock or other tube connections to mount inline
with metal or plastic tubing.
Installation drawings of each mounting type can be found in the appendix.
IMPORTANT