DIGITEL Aerosol Sampler DH-77
High Volume Sampler (HVS) Single filter unit
for autonomous and continuous measurements
The Digitel High Volume Sampler DH-77 is a system to sample dust and aerosol particles for later assessment and analysis. The sampler operation range in standard execution is 100 to 1000 litres per minute (6 to 60 cubic metres per hour). The system’s usual designation is „High Volume Sampler“.
Air-borne-dust parts in the sampled air are separated onto 150 mm diameter filters. The flown filter diameter is 140 mm. Subsequent gravimetric and analytical analysis could be conducted then depending upon the pollutants of interest. Filter material and structure selection (deep filters, porous filters, glass fibres, silica fibres, pulp, Teflon, porosity....) will depend on the analysis purpose. The filter conditioning is important in order to achieve reproducible results.
A flow meter controls the selected air flow rate. This
value should be calibrated first at the beginning of a measurement session,
using a gasmeter or a secondary standard, e.g. an additional flow meter.
During air sampling, the pump flow rate is dynamically controlled, so
that this value is kept at good reproducibility and at long-term stability
despite the deposited filter flow resistance and the sampled ambient air
pressure / temperature variation.
An integrated microprocessor unit controls filter changes at the exact
preset time and collects all relevant data and events. Hereby the air
quantity, flowing through the filter, is defined with high accuracy.
All mechanical components of the changing automatics as well as the units
needed for measurement as sampling probe, pipeline, flow chamber and filter
holder, have been improved: they are coated with highly corrosion-resistant
and extremely smooth „Ematal“.
For total suspended particulates (TSP) sampling, there are available two
differently designed sampling probes:
- a cylinder probe (EMPA/UBA probe) and
- a probe of „open ring slot“ according to VDI as described
in GMBI 1983 regarding non-fractionated dust sampling.
Sampling probes PM10/PM2.5
are designed as single-stage impactors. They are intended for operational
volume flow of 30 cubic metres per hour.
Sampling probes PM1 are designed as
double-stage impactors. They are designed for operational volume flow
of 23.1 or 30 cubic metres per hour.
Various remote-control interfaces are built in for operation in automated
measurement networks.
The Digitel DHA-80 are described in the VDI directive No. VDI 2463, sheet
11. The operating principle of the DH-77 is schematically illustrated
below.
1 Pre-separator
2 Separator
chamber
3 Current
filter
4 Microprocessor
control
5 Flow
meter
5a Flow-sensors
5b Flow-control
5c Frequency
converter
6 Blower
7 Noise
baffler
8 Pressure
and temperature
measurement
unit
9 Printer
interface
10 RS-232C
interface
11 PCMCIA
card
12 Protection
lightning print
13 Winddata
interface
11, 12 and 13 are optional
The air is sampled via a sampling
probe (1), using a sampling tube, vertically from the top to the bottom
through the filter (3) placed in the flowing chamber (2). After the filter,
the transported air quantity is measured using a flow meter with a floater
(5). Its double photo-sensor (5a) optically senses the floater position.
In connection with the control electronics (5b, 5c), the capacity of the
pump (6) is adapted to the rpm control, so that the air quantity keeps
the set-point value.
Air pressure and temperature are measured upstream the flow meter and
continuously averaged by the controller. A real-time protocol states sampling
volumes yielding from the sampling time and controlled volume flow as
the core information. The air is released from the instrument with reduced
noise through noise baffle (7).