5.3.2 Gas Table Settings
The GFM2 Mass Flow Meter is capable of storing calibration data for up to 10
different gases. Digital interface commands are provided to:
- get currently active Gas Table number and Gas name
- set desired Gas Table.
5.3.3 Totalizer Settings
The total volume of the gas is calculated by integrating the actual gas flow rate
with respect to the time. Digital interface commands are provided to:
- reset the totalizer to ZERO
- start the totalizer at a preset flow
- assign action at a preset total volume
- start/stop (enable/disable) totalizing the flow
- read totalizer via digital interface
The Totalizer has several attributes which may be configured by the user. These
attributes control the conditions which cause the Totalizer to start integrating the gas
flow and also to specify actions to be taken when the Total Volume is outside the
specified limit.
Totalizer action conditions become true when the totalizer reading and preset
"Stop at Total" volumes are equal.
Local maintenance push button is available for manual Totalizer reset on the field.
The maintenance push button is located on the right side of the flow meter inside
the maintenance window above the 15 pin D-connector (see Figure C-1 “GFM2
configuration jumpers”).
5.3.4 Flow Alarm Settings
GFM2 provides the user with a flexible alarm/warning system that monitors the Gas
Flow for conditions that fall outside configurable limits as well as visual feedback for
the user via the status LED and LCD (only for devices with LCD option) or via a
Relay contact closure.
The flow alarm has several attributes which may be configured by the user via a
digital interface. These attributes control the conditions which cause the alarm to
occur and to specify actions to be taken when the flow rate is outside the specified
conditions.
Mode Enable /Disable - Allows the user to Enable/Disable Flow Alarm.
Low Alarm - The value of the monitored Flow in % FS below which is considered an
alarm condition.
High Alarm - The value of the monitored Flow in % FS above which is considered
an alarm condition.
Action Delay - The time in seconds that the Flow rate value must remain above the
high limit or below the low limit before an alarm condition is indicated. Valid settings
are in the range of 0 to 3600 seconds.
Latch Mode - Controls Latch feature when Relays are assigned to Alarm event.
Following settings are available:
0 - Latch feature is disabled for both relays
1 - Latch feature is enabled for Relay#1 and disabled for Relay#2
2 - Latch feature is enabled for Relay#2 and disabled for Relay#1
3 - Latch feature is enabled for both relays.
The current Flow Alarm settings and status are available via digital interface (8.3
ASCII Command Set “GFM2 SOFTWARE INTERFACE COMMANDS”).
5.3.5 Relay Assignment Settings
Two sets of dry contact relay outputs are provided to actuate user supplied
equipment. These are programmable via digital interface such that the relays can
be made to switch when a specified event occurs (e.g. when a low or high flow
alarm limit is exceeded or when the totalizer reaches a specified value).
The user can configure each Relay action from 6 different options:
No Action : (N) No assignment (relay is not assigned to any events and not
energized).
Totalizer > Limit : (T) Totalizer reached preset limit volume.
High Flow Alarm : (H) High Flow Alarm condition.
Low Flow Alarm : (L) Low Flow Alarm condition.
Range between H&L : (R) Range between High and Low Flow Alarm condition.
Manual Enabled : (M) Activated regardless of the Alarm and Totalizer conditions.
5.3.6 K-Factors Settings
Conversion factors relative to nitrogen for up to 36 gases are stored in the GFM2
(see APPENDIX II). In addition, provision is made for a user-defined conversion
factor. Conversion factors may be applied to any of the ten gas calibrations via
digital interface commands.
The available K Factor settings are:
• Disabled (K = 1).
• Internal Index The index [0-35] from internal K factor table (see APPENDIX II).
• User Defined User defined conversion factor.
5.3.7 Zero Calibration
The GFM2 includes an auto zero function that, when activated, automatically
adjusts the mass flow sensor to read zero. The initial zero adjustment for your
GFM2 was performed at the factory. It is not required to perform zero calibration
unless the device has zero reading offset with no flow conditions.
Shut off the flow of gas into the Digital Mass Flow Meter. To ensure that no seepage
or leak occurs into the meter, it is good practice to temporarily disconnect the gas
source. The Auto Zero may be initiated via digital communication interface or locally
by pressing the maintenance push button, which is located on the right side of the
flow meter inside the maintenance window above the 15 pin D-connector (see
Figure C-1 “GFM2 configuration jumpers”).
To start Auto Zero locally, press the maintenance push button. The status LED will
flash not periodically with the RED light. On the GFM2 with optional LCD, the
following screen will appear:
Figure b-6: GFM2 Screen in the Beginning of Auto Zero Procedure
By default the GFM2 is shipped with at least one valid
calibration table (unless optional additional calibrations were
ordered). If instead of the valid Gas name (for example NITROGEN), the LCD
screen or digital interface displays Gas designator as “Uncalibrated”, then the
user has chosen the Gas Table which was not calibrated. Using an “Uncalibrated”
Gas Table will result in erroneous reading.
NOTICE
Before enabling the Totalizer, ensure that all totalizer settings
are configured properly. Totalizer Start values have to be
entered in % FS engineering unit. The Totalizer will not totalize until the flow rate
becomes equal to or more than the Totalizer Start value. Totalizer Stop values
must be entered in currently active volume / mass based engineering units. If the
Totalizer Stop at preset total volume feature is not required, then set Totalizer
Stop value to 0.
NOTICE
In order to locally Reset Totalizer, the reset push button must
be pressed during power up sequence. The following
sequence is recommended:
1. Disconnect GFM2 from the power.
2. Press maintenance push button (do not release).
3. Apply power to the GFM2 while holding down the maintenance push button.
4. Release maintenance push button after 6 seconds. For GFM2 with optional
LCD, when GFM2 Main Screen appears (see Figure b-4).
NOTICE
The value of the Low alarm must be less than the value of the
High Alarm.
NOTICE
The value of the High alarm must be more than the value of
the Low Alarm.
NOTICE
If the alarm condition is detected, and the Relay is assigned to
Alarm event, the corresponding Relay will be energized.
NOTICE
By default, flow alarm is non-latching. That means the alarm is
indicated only while the monitored value exceeds the specified
conditions. If Relay is assigned to the Alarm event, in some cases, the Alarm
Latch feature may be desirable.
NOTICE
The conversion factors will not be applied for % FS
engineering unit.
NOTICE
Before performing Zero Calibration, make sure the device is
powered up for at least 15 minutes and absolutely no flow
condition is established.
NOTICE
The same maintenance push button is used for Auto Zero
initiation and Totalizer reset. The internal diagnostic algorithm
will prevent initiating Auto Zero function via the maintenance push button before
the 6 minutes sensor warm up period has elapsed.
NOTICE
AUTOZERO IS ON!
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