72
microAeth
®
MA Series MA200, MA300, MA350
Operating Manual
microAeth
®
MA Series MA200, MA300, MA350
Operating Manual
73
AethLabs
AethLabs
7.3.1. Flow Calibration Table
The flow calibration table stored in the microAeth is used to control and measure the instrument’s flow
system. The instrument’s internal flow sensors and pump are calibrated to an accurate flow rate for each
setpoint in the flow calibration table using an external mass flowmeter as a reference standard. Parameters
of the environment, microAeth, and external flowmeter from the MA Series Flow Calibration Kit used to
calibrate the microAeth are also stored as part of the header of the flow calibration table.
Many commercial flowmeters are mass flowmeters. They calculate a flow 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, flowmeters most often report flow
rates not as a mass unit over time, but as a volume unit over time. The internal flow sensors are also
measuring mass flow and converting these values to volumetric values using the flow calibration table.
Only the external mass flowmeter in the AethLabs MA Series Flow Calibration Kit is compatible with
the MA200, MA300, and MA350. The external flowmeter in the microAeth MA Series Flow Calibration Kit
is a custom unit made for AethLabs specifically for the microAeth MA Series instruments to optimize the
measurement flow range for the low flow and low back pressure requirements. The flow calibration process
requires multiple calibration passes and the calibration of multiple flowmeters with multiple solenoid
switches as well as other process controls. The process must be automated and thus the microAeth
firmware has been developed to work with a specific custom flowmeter.
Other flowmeters may not be suitable for use with the MA Series instruments for a few reasons. (1) Other
flowmeters with wider flow measurement ranges may only have one or two calibration setpoints in the
full range of the MA Series instuments. (2) Many ∆P based flowmeters have higher backpressure, and as
such, very little flow 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 flow calibration process. (4) The flow 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 flowmeter.
7.3.2. Display and Check Flow Calibration Table
The flow calibration table stored in the microAeth can be viewed in order to verify that a good, complete
flow calibration table exists. A good, complete flow calibration table is critical in order to obtain the best
results from the microAeth.
To view the flow calibration table and the complete results from the previous flow 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 flow calibration table (See section 5.8.3.11 Display All Settings) or just the flow 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 flow calibration table shows a summary of the final results of the current flow calibration. Below the
flow calibration table itself is the text 'FlowCal Results:' after which the detailed summary results are
displayed. At the completion of a flow 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 flow calibration should be run.
It can take multiple flow 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 flow 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 flow 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 flow rate in
SingleSpot™ and or DualSpot
®
. 'Min Flow of 40 Not Achieved in <SingleSpot
or DualSpot> Mode (<actual minimum flow>)' 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 flow calibration
setpoints that have possible issues are marked with '*'.
FAIL MAX <xx/yy> Flow calibration completed but with failure to reach maximum flow rate
in SingleSpot™ and or DualSpot
®
. 'Max Flow of 182 Not Achieved in
<SingleSpot or DualSpot> Mode (<actual maximum flow>)' 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 flow
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
flow rates in SingleSpot™ and or DualSpot
®
. Both 'Min Flow of 40 Not
Achieved in <SingleSpot or DualSpot> Mode (<actual minimum flow>)' and
'Max Flow of 182 Not Achieved in <SingleSpot or DualSpot> Mode (<actual
maximum flow>)' 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 flow calibration setpoints that have possible issues
are marked with '*'.
