Operating Principle - Dwyer PMT2 Serie Manual Del Usuario

OPERATING PRINCIPLE

Technology
The PMT2 utilizes a highly reliable DC coupled electrostatic induction sensing
technology. The sensor probe is mounted in an airflow stream such as a pipe, duct
or stack. The inductive effect takes place when particulate passes near the probe
transferring a charge from the particulate to the probe. A microprocessor filters and
processes the signal into a output that is linear to the mass concentration of particulate.
The PTFE coated probe ensures reliable operation with all types of particulate including
moist powders and highly conductive dusts. The PTFE coated probe eliminates the
need for an air purge and keeps maintenance to a minimum.
Particulate Monitoring
The PMT2 is specifically designed to continuously monitor the particulate levels in air
flow from stacks or other emission points being passed through a filter within an air
filtration system. The transmitter should be installed in the exhaust ductwork and can
be used in conjunction with various types of bag, ceramic, cartridge or cyclone filters.
When the PMT2 is first installed a baseline reading must be measured and noted. This
baseline reading is application dependent and should be measured independently for
each installation. From this baseline the operator will monitor output signal from the
PMT2. The increase in mA output indicates a rising level of particulate in the air stream
which indicates that filters are either wearing out or broken.
The PMT2 is designed to give a proportional output based on the particulate levels in
a duct or pipe, it is not designed to output a signal based on the particulate volumetric
flow. Different types of particulate carry different charges, meaning that two particulates
flowing at the same volumetric flow rate could have different output response. The
PMT2 is designed to find a baseline under ideal operating conditions and allow an
operator to watch the output signal for increases that would signify the bags or filters
are starting to wear or break. The six sensitivity ranges allow the PMT2 to monitor
particulates with low charge properties or high charge properties. As a reference, Table
1 lists particulate charge properties and the suggested range.
Particulate
Human Hands
Asbestos
Rabbit Fur
Acetate
Glass
Mica
Human Hair
Nylon
Wood
Fur
Lead
Silk
Aluminum
Paper
Neutral Cotton
Steel
Wood
Mylar™
Nickel/Copper
Silver/Brass
Gold/Platinum
Sulfur
Acetate Rayon
Polyester
Styrene (Styrofoam)
Acrylic
Saran™
Polyurethane
Polyethylene
Polypropylene
Vinyl (PVC)
Silicon
PTFE
Silicone Rubber
Table 1: Suggested Ranges
Suggested Range
5 to 5000 pA
5 to 1000 pA
5 to 500 pA
5 to 100 pA
5 to 500 pA
5 to 1000 pA
5 to 5000 pA
INSTALLATION
Unpacking
Remove the PMT2 from the shipping carton and inspect for damage. If damage is
found, notify the carrier immediately.
Location
The following factors should be considered when determining the installation location
for the PMT2:
• Make sure the transmitter is rated for the area classification it will be mounted in.
• Mount the transmitter in a location that will not exceed the temperature and pressure
ratings listed in the specifications. The process pressure should not exceed 30 psi (2
bar).
• Make sure the 4-20 mA signal wires are not sharing the same conduit with high
voltage power wires.
• Make sure the location the transmitter is mounted in meets the NEMA or IP rating
for the enclosure.
• Locate the transmitter in a location were it can be accessed in case service is
required.
The PMT2 should be mounted in a grounded metal stack, pipe or duct. It should not
be mounted in fiberglass or plastic stacks, pipes or ducts. The sensing probe should
reach 1/2 to 2/3 the way across the stack, pipe or duct to ensure accurate readings.
For the most stable and accurate readings it is recommended to mount the PMT2 in
a location where the air flow is as laminar as possible. Avoid mounting the transmitter
close to blowers and dampers that cause turbulence. It is ideal to mount the PMT2 in
an area with two upstream duct diameters and one down stream duct diameter that
are free of turbulent causing objects. The sensing probe is coated in a non-stick PTFE
preventing material from coating the probe reducing the need for cleaning or an air
purge.