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INSTALLATION
GAS INLET
ISOLATION VALVE
GAS INLET
GAS INLET
ISOLATION VALVE
GAS INLET
Figure 7
2.7
Sample Gas Flows
The flow through each channel should be set at approximately 2 Nl/min (4.2 scfh). This
flow setting figure is not required to be precise. Its purpose is only to ensure that a
representative sample of gas is presented to the measurement sensor.
To increase the speed of response of the measurement of the main process gas it is
highly recommended that a fast bypass loop be installed into the gas sampling system.
The recommended flow through the bypass loop should be approximately 3 times that
of the measurement channel. Therefore, typically, the bypass gas flow should be set to
approximately 6 Nl/min (12.7 scfh).
2.8
Sample Flow Alarms (Optional)
The optional flow switches are supplied to alert the user to either severely reduced
or discontinuation of the sample gas flow through the system. An alarm state will be
indicated on the error message line at the bottom of the MAIN Page. See Section 4.4 on
troubleshooting for further details.
When the flow of sample gas is set correctly, the alarm states will be indicated when
the gas flows have lowered into a range deemed unsuitable for effective measurements
to be made.
The flow switches are adjusted during factory test to activate the alarm when the
flow falls below approximately 10 to 20% of the normal recommended sample flow
setting (see Section 2.7). During the factory setting procedure the gas pressure that
is applied represents the most common application analysis conditions for water dew-
point sensors {68 barg (986 psig)}. The operation of these variable area flow switches
are influenced by pressure. For increased pressure the flow alarm activation point will
be at a higher flow rate and conversely, for reduced pressure, the activation point will
be at a lower rate. These devices exhibit a hysteresis that may require a flow of greater
than 100% of the recommended flow setting for a brief period in order to clear the
alarm condition.
NOTE: If the Promet EExd is going to be operating with significantly different
analysis pressures to those used during factory testing then fine re-adjustment
of the flow switches may be beneficial to suit the application conditions. If
this is the case, contact Michell Instruments (www.michell.com) for guidance
on how adjustments can be made on site.
16
MINIMUM REQUIREMENTS FOR START UP PURGING
PRESSURE
GAUGE
PRESSURE
REGULATOR
WATER DEW-POINT
GAS IN
PRESSURE
PROMET EExd
GAUGE
PRESSURE
REGULATOR
GAS IN
WATER DEW-POINT
NOTE:
CONNECTING PIPEWORK TO BE 4mm I/D BORE, 316L STAINLESS STEEL TUBE
Minimum Requirements for Start-up Purging
Promet EExd User's Manual
FLOWMETER
CHANNEL-1
GAS OUT
FLOWMETER
GAS OUT
CHANNEL-2
97090 Issue 16.1, November 2019
NON-RETURN
VALVE
GAS OUTLET
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