Datex-Ohmeda Anesthesia Delivery Unit S/5, Техническое справочное руководство

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Technical description A-FGC1
Document No. 8502854
B-5
Description of the flow control section
Pressure regulators
The fresh gas flow range is set with three regulators for each gas. The regulators control the secondary
pressure to a fixed level that is independent on the pipeline pressure. The O
2
, N
2
O and Air lines (1) are
supplied to the A-FGC1 at normal pipeline pressure and separate gas regulators (3) for each gas
reduce the pressure to the gas controls of the unit.
The nominal maximum flows when the needle valves are fully open, are 14 l/min. for O
2
and Air and
12 l/min. for N
2
O. The allowed flow range is 12 - 16 l/min. for O
2
and Air. For N
2
O the range is 8.5 - 11
l/min. with a simultaneous O
2
flow of 4 l/min.
The flow decreases when another gas is added. The second flow increases the counter pressure that
causes the regulator to decrease the flow to keep the secondary pressure at a constant level. The
effect is specified in the “Technical specifications” section.
Flow controls and flow measurement
The flows are adjusted by means of mechanical needle valves (4) and electrical flow measurement
unit's measures the gas flows.
There are two different combinations of needle valves on the front panel, ISO and ANSI. The
combination, color and the shape of the control knobs is dependent on the regulatory requirements
in each country.
The needle valves are linear. One full turn corresponds approximately to a 2-3 l/min. change of the
flowrate. The needle valve adjustment should be smooth without any sticking and/or sudden
changes in the flow.
There is one flow measurement unit for the O
2
flow (10) and one unit for the N
2
O/Air flow (11), called
sidegas. The sidegas sensor is calibrated for both gases. The N
2
O flow may be adjusted up to 75% of
total flow which assures a minimum of 25% O
2
in the fresh gas outlet.
The flow measurement units determine the gas flow from the pressure difference caused by a flow
restrictor. By using a zeroing valve, which pneumatically short circuits the differential pressure sensor
ports periodically, the zero pressure signal is compensated for the pressure sensor temperature drift.
The same types of flow measurement units are used in the vaporizer.
Each flow measurement unit has a:
•
Pressure Sensor Board
The output voltage of the pressure sensor (tens of millivolts) is amplified to a level which is suitable for
the A/D converter in the CPU board of the fresh gas control unit. The gain of each amplifier is set
according to the type of the sensor being used and the pressure signal of the measurement unit.
•
Flow Restrictor
The gas flow in the flow restrictor is close to laminar thus causing a pressure difference linear to the
flow. The restrictor causes a pressure drop that is measured by the pressure sensor. The pressure
difference is then used to calculate the flow through the flow measurement unit. The mixer flow
measurement units are designed to give the maximum signal (10V) at 20 l/min. A 15 l/min. flow
produces nominally a 140 mbar pressure drop over the flow restriction.
•
Zeroing Valve
A zeroing valve is used to compensate the pressure sensor temperature drift that causes variation of
the zero point signal. The valve connection is shown in the figure. In powered position the pressure
sensor ports are pneumatically connected thus giving the zero pressure signal. In the normal position