Section 6: Hardware Description
Airmetrics
49
of the unit. T he pum ping sectio ns consis t of synthe tic rubber d iaphragm s housed in
molded plastic casing directly driven from the motor shaft by a scotch yoke-crank
assembly. Valves are of the self-biasing fiberglass reinforced synthetic rubber type.
No metallic springs are used in the blower. The air pumped contacts only the
plastic and synthetic rubber areas. All moving parts are completely enclosed. The
service life of the motor is in excess of 10,000 hours continuous duty. The
diaphragm valve assemblies are easily replaceable. The service life expectancy of
these assemblies are a function of the environmental conditions, including the gases
being pumped, delivery rate, and back pressure. Minimum service life for the
pumping sections is on the order of 5000 or more hours continuous duty.
The m otor gene rates no ra dio freque ncy interfe rence an d all electron ic comp onents
are contained within the motor housing. Overall weight is 12.1 ounces (344
grams).
Electronics System
M
OTHERBOARD
Virtually all sampler components connect to the motherboard--the pump,
programmable timer, elapsed time totalizer, flowmeter, and flow control
comp onents. F low con trol, intervalo meter, an d fault circu its, are built into this
board, and pins are provided on the back side to mount the solenoid board for dual
bag sampling.
P
OWER
S
UPPLY
The sam pler is pow ered by re mova ble battery packs w hich con tain a 12 v olt,
12 amp-hour sealed lead-acid battery and a stepped output charger circuit. The
charger c ircuit is pow ered by a n 18 volt A C extern al powe r supply. T he charg er is
designe d to quick -charge th e battery a nd then s witch to a "mainte nance" mode to
avoid an overcharge condition. The charger can be left on for an indefinite period
without damaging the battery.
P
ROGRAMMABLE
T
IMER
The Programmable Timer can switch power on and off up to 6 times per day over
a 7-day period and is capable of individual or multi-day timer settings. It has an
Airmetrics MiniVol Users Guide
50
Airmetrics
easy to read liquid-crystal display and its own power supply.
F
LOW
C
ONTROLLER
C
IRCUIT
The Flow Controller Circuit is designed to maintain a constant pressure drop
across an orifice at the output of the flowmeter. Feedback from the pressure sensor
is used to control the p ump spee d by supplying variable voltage to the p ump m otor.
The system is temperature compensated and is capable of maintaining a constant
volumetric flow rate within ±5% of the set point over the range of 0 to 40°C.
E
LAPSED
T
IME
T
OTALIZER
The Elapsed Time Totalizer is a non-resetable time totalizer which is activated
when th e program mable tim e controlle r is in the "O N" m ode. Th e meter to tals
hours and tenths of hours.
I
NTERCONNECT
B
OARD
The Interconnect Board is located in the bottom of the sampler case. Power from
the battery pack is routed through banana pins on the outside of the sampler bottom
to the Interconnect Board. A phone plug in jack and cable is used to connect power
to the mo therboard . A 2 am p fuse on the interco nnect bo ard prov ides prote ction to
the motherboard from short circuits and high current loads.
M
OTHERBOARD
E
LECTRONICS
S
CHEMA TIC
See Figu re G.3 ins ert at the end of this M anual.
B
ATTERY
P
ACK
C
HARGER
E
LECTRONICS
S
CHEMA TIC
See Figu re G.4 ins ert at the end of this M anual.
V
ALVE
D
RIVER
B
OARD
E
LECTRONICS
S
CHEMA TIC
See Figu re G.5 ins ert at the end of this M anual.
