Measurement Principle
As analytical detection
method we use the well proven atomic absorption spectrometry (AAS) to
get maximum analytical performance and measurement accuracy for
mercury concentrations within 10 ppt (parts per trillion) to 10
ppm (parts per million)!
The mercury
concentration is measured in an optical cell made of fused silica. A
maintenance-free membrane pump continuously feeds the sample gas to
the optical cell where light absorption measurement takes place at a
wavelength of 253.7 nm.
Figure: Schematic
diagram of the AAS measuring-cell unit
This
so-called "cold vapor atomic absoption spectroscopy" (CVAAS)
is extremely sensitive for mercury determination and has been used
successfully for many years.
All of our analyzers
use a high-frequency driven electrodeless Hg low pressure discharge
lamp (EDL) as UV light source. It generates emission
lines of an extremely narrow bandwidth which are congruent with the
absorption lines of the Hg atoms. Cross - sensitivities are thus
minimized.
Further advantages of
the EDL in respect to conventional Hg low pressure discharge lamps are
longer life, higher stability as well as easy and precision intensity
controlling.
The extremely high
stability of our UV source is a result of the reference beam
method. To prevent temperature drift both the lamp unit and the
detectors are temperature stabilized.
The CVAAS, in contrast
to the occasionally recommended atomic fluorescence method, is low in
interference and requires neither an amalgamation step nor expensive
noble gases as carriers.
We at MI have a 10 year
experience in the engineering of customized mercury monitoring systems
and provide solutions for individual and special applications.
The VM 3000 Mercury
Vapor Monitor
This is the
first commercially available continuous emission monitor
(CEM) for stack gases, the Stack Monitor SM-3, with a new
operating principle, based on the thermo-catalytic method. Wet
chemical sample gas treatment using reagents and bubblers is avoided!
- Continuous operation
- Proven reliable
detection method:UV absorption
- Easy operation
- Auto zero
- Measuring ranges
1-100 / 1-1000 / 1-2000 µg/m3
- Heated measurement
cell
- Integrated battery
for mobile use (optional)
- Can be converted to
a laboratory device for liquid samples and sample digestion.
The VM-3000 Mercury Vapor
Monitor serves for continuous measurement of the mercury concentration
in gases in laboratory as well as industry and mobile applications.
It has a wide variety
of applications, such as work place monitoring (threshold limit
value), exhaust air monitoring in mercury recovery plants, emission
monitoring in the chemical industry, ground air screening of
contaminated soil, quality control of hydrogen and natural gas,
detector for laboratory applications.
- Metal housing with
sturdy handle
- Option: Rack version
with mounting brackets for 19" racks
- Membrane pump with
long service life
- Input filter with
teflon membrane
- Stable optical bench
- Factory-calibrated
The user controls the
VM-3000 by menu-guided inputs via a waterproof membrane keypad. After
switch-on the light source is stabilized (approx. 1 - 5 minutes). When
the measurement mode is started, a zero adjustment is first carried
out automatically. Then the analyzer switches to measurement and
continuously indicates the measured mercury content of the gas as a
numerical value and a graphic bar.
The following settings
are possible in the "parameters" menu: duration and repeat
interval of the zero adjustment, selection of the concentration unit
(µg/m3 or ppb), measuring range (1-100, 1-1000, 1-2000 µg/m3), input
of three different alarm levels, calculation of a mean value over
three freely selectable time intervals, printer activation, and, if
required, a sample dilution factor.
The result of the
measurement is displayed on an LCD in real time, both numerically and
graphically and is output as an electrical signal of 4-20 mA..
The device has outputs
for alarm, status and measurement values for full integration in plant
control systems. The device also has a serial interface (RS 232) for
data collection on a PC.
The VM-3000 Mercury Vapor
Monitor is the basic model of our modular system for mercury
analytics. An optional reaction unit and activation of the relevant
software turns it into a laboratory unit for liquid samples.
A gold trap installed
upstream allows measurements in the extreme trace range.
If an important component
of the VM-3000 malfunctions the user is warned via the display
(blinking messages: clean cell, lamp, low batt., alarm) and via output
signals.
For mobile use the VM-3000
is also available with a built-in rechargable battery and a charger
unit. This option allows mobile battery-powered applications of up to
approx. 5 hours.
A multiplexor unit can be
connected for automatic monitoring of several measuring points, e.g.
as a cellroom monitoring system for chlorine plants.
Such a Mercury
Monitoring System MMS consists of the Mercury Vapor Monitor
VM-3000 , the multiplexor valve unit , the sample bypass
pump and two flowmeters. These components are mounted in a
industrial grade (IP 65) magnetically shielded enclosure.
MMS Features:
- 2 to 16 sampling
points
- Up to 48 points by
linking several units
- Permanent purging of
non-active sampling lines
- Analytical
resolution 1 µg/m³ Hg
- Stand alone unit or
in combination with a PC
- data transfer via RS
485 interface > 100 m distance
- Software for control
and Data aquisition by PC
- Industrial grade
design with magnetic shielded enclosure
- Heated multiplexor
valves as an option
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Mercury
Analyzers & Mercury Monitors
At
GMI...its instrumental !