Section 3: C ontrols and Adjustm ents
Airmetrics
17
ON/AUTO/OFF
B
UTTON
The ON/AUTO/OFF Button manually turns the sampler on, off, or places it in the
"Auto" mode. In the "Auto" position, the sampler is controlled by whatever
programmed on/off sequences have been entered. A bar on the lower edge of the
Programmable Timer's LCD display moves from "On" to "Auto" to "Off" as the
button is pressed (see "Program ming the Tim er" in Section 2).
Integrated Gas Sampling Option
Integrated bag filling is accomplished with a Valve Driver Circuit board that plugs
into the auxiliary connector on the back of the sampler motherboard. The Valve
Driver Board controls the operation of the two solenoid valves that are mounted on
the board. This arrangement allows for collection of one or two bag samples during
a user selected sampling period. For example, this option allows for collecting two
4- or 8-hour integrated bag samples.
Function ally, sam ple gas is su pplied to th e comm on inlet po rt of each n ormally
closed solenoid valve by the constant back-pressure of the flow control system. The
sampler pump operates continuously at a pre-set flow rate to purge the system and
supply sample gas to the solenoids under pressure. The output port of each
norma lly closed s olenoid v alve is con nected to a bag m odule. B ecause th e pum p is
operating continuously during the sampling period, a PM sample may be collected
concurrently with the integrated gas samples.
Electronically, the Valve Driver Board interacts with the Programmable Timer on
the moth erboard to perform two func tions: 1) co ntrol whic h soleno id valve is
activated, and 2) set the duration and frequency of the "on" time for the active
solenoid valve.
A 4-step circular sequencing circuit advances each time the programmable timer on
the motherboard is switched from the "Auto" to the "Off" mode. There are four
solenoid output connectors with corresponding indicators located in the upper
lefthand corner of the board that the solenoid valves can be plugged onto. The
indicators show the output that is, or will be, active when the sampler is switched
to the "O n" mo de either m anually o r by prog ramm ed opera tion. Wh en a solen oid
output is ac tive and th e samp ler is in the "O n" mo de, a solen oid valve plugged onto
the active o utput pins is opened and close d by a tun able interv alomete r circuit.
Both frequency and duration of solenoid valve operation are adjustable to allow the
Airmetrics MiniVol Users Guide
18
Airmetrics
user maximum flexibility in controlling the bag filling rate.
S
OLENOID
V
ALVE
O
UTPUT
C
ONNECTORS
The Solenoid Valve Output Connectors connect the solenoid valves to the
sequen cing circu it.
A
CTIVE
S
OLENOID
O
UTPUT
I
NDICATORS
The Active Solenoid Output Indicator LED above each Solenoid Valve Output
Conne ctor indica tes whe n that set of p ins is active. When active the T unable
Intervalometer will open and close the solenoid valve plugged into the
corresponding connector.
M
ANUAL
S
EQUENCE
A
DVANCE
B
UTTON
The M anual Se quence Advan ce Button allows th e operato r to select w hich Sole noid
Valve Output Connector will be active when the pump is turned on. The Manual
Advance only functions w hen the pum p is off. Each time th e pump is turn ed off,
the channel advances automatically.
P
ULSE
I
NTERVAL
A
DJUSTMENT
The Pulse Interval (off time) of the circuit is adjustable over a range of 0-15
seconds by a 16-position rotary switch. This switch is located just to the right of
the solenoid valve output connectors. Switch positions are marked clockwise 0-9,
and continue A-F. The interval between pulses increases in 1-second increments as
the switch is rotated in a clockwise direction. Position "0" enables continuously on.
Position "1" corresponds to a minimum delay time of one pulse per second, and
position "F" indicates the maximum delay of 15 seconds between pulses. The fine
adjustment potentiometer next to this control is for calibrating the one-second
interval (fully counterclock wise - decrease , fully clockwise - increa se).
P
ULSE
D
URATION
A
DJUSTMENT
The duration (on time) of each pulse is adjustable over a range of 50-750
milliseconds (ms). This adjustment is made by summing the calibrated interval
values of the dual in-line package (DIP) switches 1-4 on the 5-position DIP switch
located in the upper right corner of the auxiliary board. Each switch has an
