72 microAeth
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MA Series MA200, MA300, MA350 Operating Manual microAeth
®
MA Series MA200, MA300, MA350 Operating Manual 73
AethLabsAethLabs
7.3. Flow Calibration
7.3.1. Flow Calibration Table
The ow calibration table stored in the microAeth is used to control and measure the instrument’s ow
system. The instrument’s internal ow sensors and pump are calibrated to an accurate ow rate for each
setpoint in the ow calibration table using an external mass owmeter as a reference standard. Parameters
of the environment, microAeth, and external owmeter from the MA Series Flow Calibration Kit used to
calibrate the microAeth are also stored as part of the header of the ow calibration table.
Many commercial owmeters are mass owmeters. They calculate a ow rate by measuring the amount of
gas molecules (or mass of the gas) moving through the device during a certain amount of time. However,
because we commonly measure gases such as air as the volumes they occupy (as cc’s or liters, for
instance), usually at standard atmospheric pressure and temperature, owmeters most often report ow
rates not as a mass unit over time, but as a volume unit over time. The internal ow sensors are also
measuring mass ow and converting these values to volumetric values using the ow calibration table.
Only the external mass owmeter in the AethLabs MA Series Flow Calibration Kit is compatible with
the MA200, MA300, and MA350. The external owmeter in the microAeth MA Series Flow Calibration Kit
is a custom unit made for AethLabs specically for the microAeth MA Series instruments to optimize the
measurement ow range for the low ow and low back pressure requirements. The ow calibration process
requires multiple calibration passes and the calibration of multiple owmeters with multiple solenoid
switches as well as other process controls. The process must be automated and thus the microAeth
rmware has been developed to work with a specic custom owmeter.
Other owmeters may not be suitable for use with the MA Series instruments for a few reasons. (1) Other
owmeters with wider ow measurement ranges may only have one or two calibration setpoints in the
full range of the MA Series instuments. (2) Many ∆P based owmeters have higher backpressure, and as
such, very little ow will be drawn through the instrument. (3) Bubble meters are far too slow to be used
with the MA Series instruments in the required automated ow calibration process. (4) The ow calibration
of MA Series instruments must be automated because the process is complicated with multiple solenoid
switches and a high possibility for human error, therefore it requires a direct communication interface with
the external owmeter.
7.3.2. Display and Check Flow Calibration Table
The ow calibration table stored in the microAeth can be viewed in order to verify that a good, complete
ow calibration table exists. A good, complete ow calibration table is critical in order to obtain the best
results from the microAeth.
To view the ow calibration table and the complete results from the previous ow calibration, the on-board
user interface on the front of the microAeth is used to send all settings information of the instrument which
includes the ow calibration table (See section 5.8.3.11 Display All Settings) or just the ow calibration
table information (See section 5.8.3.12. Display FlowCal Info) via the 4-pin serial port to a terminal emulator
(AethLabs only supports Tera Term for Windows) on a computer using the AethLabs 4-pin Serial to USB
converter cable.
7.3.2.1. Flow Calibration Table Results Descriptions
The ow calibration table shows a summary of the nal results of the current ow calibration. Below the
ow calibration table itself is the text 'FlowCal Results:' after which the detailed summary results are
displayed. At the completion of a ow calibration, the same abbreviated results shown in the 'Result'
column of the below table are displayed on the LCD screen. If results other than 'OK <yy/yy>' are
displayed then another ow calibration should be run. It can take multiple ow calibration attempts to
achieve the best calibration.
FlowCal Results
Result Description
OK <yy/yy> Flow calibration completed sucessfully. A complete table without warnings or
failures occurred. 'yy' equals the amount of ow calibration setpoints that were
calibrated. yy/yy = 100% (Example: OK 35/35)
WARNING <xx/yy> Flow calibration completed sucessfully but with warnings to review. 'Review
rows marked with *' will be displayed below 'FlowCal Results: WARNING <xx/
yy>' and all ow calibration setpoints that have possible issues are marked
with '*'. xx/yy < 100% (Example: WARNING 34/35)
FAIL MIN <xx/yy> Flow calibration completed but with failure to reach minimum ow rate in
SingleSpot™ and or DualSpot
®
. 'Min Flow of 40 Not Achieved in <SingleSpot
or DualSpot> Mode (<actual minimum ow>)' will be displayed below 'FlowCal
Results: FAIL MIN <xx/yy>' where xx/yy <= 100%. If xx/yy < 100%, then
'Review rows marked with *' will also be displayed and all ow calibration
setpoints that have possible issues are marked with '*'.
FAIL MAX <xx/yy> Flow calibration completed but with failure to reach maximum ow rate
in SingleSpot™ and or DualSpot
®
. 'Max Flow of 182 Not Achieved in
<SingleSpot or DualSpot> Mode (<actual maximum ow>)' will be displayed
below 'FlowCal Results: FAIL MAX <xx/yy>' where xx/yy <= 100%. If xx/yy
< 100%, then 'Review rows marked with *' will also be displayed and all ow
calibration setpoints that have possible issues are marked with '*'.
FAIL MIN MAX <xx/yy> Flow calibration completed but with failure to reach minimum and maximum
ow rates in SingleSpot™ and or DualSpot
®
. Both 'Min Flow of 40 Not
Achieved in <SingleSpot or DualSpot> Mode (<actual minimum ow>)' and
'Max Flow of 182 Not Achieved in <SingleSpot or DualSpot> Mode (<actual
maximum ow>)' will be displayed below 'FlowCal Results: FAIL MAX <xx/yy>'
where xx/yy <= 100%. If xx/yy < 100%, then 'Review rows marked with *' will
also be displayed and all ow calibration setpoints that have possible issues
are marked with '*'.
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