Galvanic Applied Sciences 943-TGS, Operation Manual

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Revision 1 30 6/27/2017
3.2.4 Aspirator Drive Air Flow Adjust Valve
The Aspirator Drive Air Flow Adjust Valve controls (indirectly) the rate of process sample gas
extraction from the tail gas duct. The aspirator drive air is plumbed to a venturi type eductor
integral to the measurement cell block. The design of the analyzer sample system is such
that process sample gas is extracted from near the centre of the process duct, and vented at
the wall of the process duct through the same access port. Ideally, enough aspirator drive air
is provided to present a measurement cell pressure of 2-3" H2O below the process duct
pressure.
In practice, the aspirator drive air flow adjustment is made to obtain a nominal 5-10 second
stabilized sample response time from a ‘zeroing’ state. (The length of time is impacted by the
actual probe length.) This adjustment is made by monitoring the time required for the
analyzer display outputs of gas concentration to return to a stable process level, after the
‘zero’ state has been released.
3.2.5 System Regulator
The system regulator is normally set to 30 psig. The absolute value of this setting is not
critical for system operation however, sufficient pressure to provide adequate sample
aspiration and system zeroing is necessary. In situations where additional supply pressure is
required, the
system regulator
may be adjusted to its maximum output of 50 psig without
harming the analyzer.
3.3 Analyzer Outputs
The 943-TGS analyzer generates both analog and digital output signals for connection to the
users’ plant control system. The analog signals include the calculated Air Demand, and the
measured concentrations of H
2
S, SO
2
, and optionally a user selectable signal for analog
output 4. The provided digital signals (relay contacts) represent indications of the current
analyzer and enclosure purge state.
3.3.1 Analog Outputs
The
analog outputs
are ranged in software, based on information provided specifically for a
particular plant. Four loop powered 4 – 20 mA outputs are available. Each output can be
configured to represent Air Demand, H
2
S, SO
2
, Sigma S (the sum of H
2
S and SO
2
concentrations), CS
2
or H
2
S/SO
2
ratio.
Each output can be programmed to be either Track or Hold. If the output is programmed to
be ‘Track’, the output will track the calculated values displayed on the Front Panel of the
computer. (Tracking outputs will follow the zero calibration sequence as it occurs.) If the
output is programmed to be ‘Hold’, the output will track the calculated value displayed on the
Front Panel until an abnormal condition, zero calibration or fault condition exists. The output
will then be held until normal operation is re-established.
The Air Demand
analog output
is Hold only. When the analyzer is in normal operation, the
Air Demand analog output tracks the displayed value. When an abnormal condition, zero