Fluke VT Plus HF Operator's Manual page 128

VT Plus HF
Operators Manual
If fluid enters into the pressure measurements connections of the Analyzer, it is important
to evacuate the fluid before storage and before any pressure measurements are made. The
fluid can be evacuated by connecting a 100 cc syringe directly to the pressure
measurement connection and then pulling back the syringe to create a vacuum.
Internal Pressure Measurements
The Analyzer also has several internal pressure measurements. These include barometric
pressure, differential pressure for the flow measurement, and airway pressure.
Airway pressure is measured internally in the tube for the flow sensors. This is done for
convenience for the user while measuring ventilator parameters. Having a pressure
measurement for airway pressure in addition to the external low-pressure measurement
ensures that the pressure is measured at a consistent location and eliminates the need for
cumbersome adapters for placing pressure taps in the airway circuit.
When the Analyzer is set to measure from the high-flow port, the airway pressure is
measured from the high-flow port. Likewise, when the low-flow range is selected, the
airway pressure is measured from the low-flow port. In both cases, the airway pressure
measurement is made on the exhaust side of the flow sensor.
Zeroing the Pressure Signals
The zero reading (offset) of the pressure measurements may drift slightly with time and
temperature. A zeroing function is provided for the user to zero the offset drift. Typically,
this is done when a non-zero reading occurs when there is zero applied pressure.
However, it is good practice to zero the respective signal before any measurement is
taken.
Although a five-minute warm-up period is built into the Analyzer power-up cycle, a 40-
minute warm-up period is suggested for maximum measurement accuracy and stability.
The offset drift is most significant while the sensors for the pressure measurements are
warming up. If the warm-up period is skipped, be aware that the offset drift may be
significant for the first 40 minutes of operation. If the Analyzer has been through an
extreme temperature change, additional time may be required for the warm-up. If the
Analyzer has only been turned off for, say a minute, the warm-up period may be skipped.
The zeroing function for pressure acts as a tare function. As such, the applied pressure
when the signal is zeroed is saved as the new zero reading. The applied pressure during
zero would then be read as zero. Measured pressures would have an offset error equal to
the applied pressure when the Analyzer was zeroed.
Airway Zeroing, A Special Case
The airway pressure may be zeroed manually using the ZERO/7 key while the airway
pressure screen is active. The airway pressure is also zeroed automatically when the flow
zero occurs. Note that the flow zero may either be performed manually or in an auto zero
mode.
Barometric Pressure, Another Special Case
The offset drift can be adjusted on the barometric pressure measurement by entering the
correct barometric pressure on the Setup > Settings menu. Although typically not
needed, it provides a means for the user to ensure that the barometric pressure
measurement is as accurate as possible.
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