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©Copyright 2012 LDetek inc. • 271, Saint-Alphonse Sud, Thetford Mines (Quebec) Canada G6G 3V7
Optical Filter and photo-diode
Optical filter is made specifically for LDetek specifications with
properties to avoid interferences, temperature drift, loss of
sensitivity and wavelength shifting over time. The wavelength,
size, transmission lines and material are all critical
characteristics that need special care to obtain such good
performances.
The photo-diode will then convert the light out of the filter to
current that is proportional of the amount of nitrogen in the
sample. An electronic circuit designed by LDetek is then used
for precision treatment of analog signal coming out of the
photodiode.
Even if it sounds straightforward, LDetek has a unique way to
install and align all items together. LDetek established
rigorous procedures in a way to achieve high and same
performances for each unit.
Figure 3
:
Plasma Detector module in the LD8000
FLOW CONTROL
Flow management in such analyzer is critical in terms of dead volume and leakage. It is important to have a flow control device that
will not introduce air and dead legs in the system. The LD8000 has an operating range as low as 0-1 ppm with a few ppb as detection
limit. Conventional Mass Flow Controllers (MFC) is not suitable for such analysis. Since air is made of 78% of nitrogen, the chance to
have some nitrogen introduced in the system with MFC is too high.
LDetek has designed its own flow control system to avoid air infiltration by the flow control device. The instrument can work with a flow
as low as 25 cc/min and have a quick response time without apparition of dead volume.
Micro-Valve
LDetek have worked to develop a valve that meets the
performances requirement. This miniature valve has a very
small orifice size and offers ultra low flow rate. Since the
LD8000 can work on relatively low flow, this valve design does
not introduce delay or drifting problems.
Standard valves (figure 5) introduce “spikes” in the reading
caused by dead volume located inside the valve. Measuring in
so low concentration can be a big problem when having
nitrogen released after calibration or upset condition in the
sample.
With the LDetek micro-valve performance (figure 6), this
problem is avoided and stable reading is obtained after any
changes of concentration.
The inlet pressure can range from low as 4 PSIG to 30 PSIG
without reading fluctuation. With an optional pump offered by
LDetek, the instrument could work in even lower pressure.
Figure 4
:
Micro-Valve for sample control