Fluke Biomedical VT Plus HF - Manual (Page 130)

VT Plus HF
Operators Manual
A-4
Note
Never apply humidified gases to the Analyzer flow sensors.
Condensation on the flow sensors causes errors in the flow readings until it is dried off.
Balance Gas Settings
The gas settings allow for gas combinations with oxygen. For example, the Analyzer can
be set to use Helium balance Oxygen. In this mode, the Analyzer uses the oxygen
measurement to determine the oxygen concentration and then assumes the balance of the
gas concentration is helium. The Analyzer calculates the effective viscosity for the
combination gas at the specified temperature. The oxygen concentration used in the gas
setting for the balance gases is automatically updated every second.
Note
For air / oxygen mixtures use the nitrogen balance oxygen (N
2
bal O
2
) gas
setting. The flowing gas is assumed to be dry and therefore the relative
humidity used in the viscosity calculation is assumed to be zero percent.
BTPS and STPD Corrections
The Analyzer corrects all flow measurements to conditions of ambient temperature and
pressure without adjusting for the volume of water vapor. The ambient pressure is
obtained from the measured barometric pressure. The user sets the ambient temperature
by using the setup menu. It should be noted that the relative humidity setting on the
Analyzer is used only for the BTPS and STPD correction.
BTPS stands for Body Temperature and Pressure Saturated with water vapor. In this
compensation mode, the flow rate (and therefore, volumes) are corrected such that the
reported flow is equal to the flow if the gas temperature and pressure were changed to
body conditions (37 °C and ambient pressure). Further, the flow is compensated to add
the amount of water vapor as if to make the gas fully saturated (100 % relative humidity).
In this correction, the relative humidity setting is used to determine the amount of water
vapor that must be added.
STPD0 stands for Standard Temperature and Pressure Dry. In this compensation mode,
the flow rate (and therefore, volumes) are corrected such that the reported flow is equal to
the flow if the gas temperature and pressure were changed to standard conditions (0 °C
and 760 mmHg). Further, the flow is compensated to subtract the amount of water vapor
as if the gas were dry (0 % relative humidity). In this correction, the relative humidity
setting is used to determine the amount of water vapor that must be subtracted.
STPD21 stands for Standard Temperature and Pressure Dry. In this compensation mode,
the flow rate (and therefore, volumes) are corrected such that the reported flow is equal to
the flow if the gas temperature and pressure were changed to standard conditions (21°C
and 760 mmHg). Further, the flow is compensated to subtract the amount of water vapor
as if the gas were dry (i.e. 0 % relative humidity). In this correction, the relative humidity
setting is used to determine the amount of water vapor that must be subtracted.
Flow Zeroing
The differential pressure transducer used to measure the flow rate is subject to baseline
(offset) drift. This is most pronounced during the Analyzer warm-up period. The
Analyzer provides both a manual and an automatic zero function for zeroing the flow.
In measuring flow, the same pressure transducer is used for both high- and low-flow
ports. A set of valves selects between high- and low-flow ranges. Because one pressure
transducer is used for both, zeroing one flow range also zeros the other.