Fluke Biomedical VT Plus HF - Manual (Page 127)

A-1
Appendix A
Gas Analyzer Tutorial
The Analyzer measures the basic signals of pressure, flow, and oxygen. From these basic
signals, other parameters are computed. Volume is obtained from the integration, or
summation, of the flow signal over a period of time.
Pressure Measurements
The Analyzer provides several pressure measurement capabilities. There are two external
pressure measurements and three internal pressure measurements available to the user.
External Pressure Measurements
These measurements are called Low Pressure and High Pressure. The low-pressure
measurement has a range of ±500 mmHg (about 10 psi). The high-pressure measurement
has a range of ± 100 psi (about 5200 mmHg).
Both high and low pressures are differential measurements. As such, the measured
pressure is the pressure difference between the positive and negative ports. If only one of
the pressure connections is made, the measurement is equivalent to a gauge
measurement. For gauge pressures, the measurement is relative to the ambient pressure.
This is how a normal pressure gauge works.
If a positive gauge pressure is applied to the (+) measurement port, a positive pressure
reading results. If a negative gauge pressure is applied to the (+) measurement port, a
negative pressure reading results. Likewise, if a positive gauge pressure is applied to the
(-) measurement port, a negative pressure reading results. If a negative gauge pressure is
applied to the (-) measurement port, a positive pressure reading results.
Fluidic Pressure Measurements: The (+) connection for both high and low pressures are
labeled as compatible with either fluids or gases. When measuring fluidic pressures, it is
important to realize that any fluid entering the pressure measurement port or the
connecting tubing may cause a bias (error) in the measured pressure. For example, if a
fluidic pressure measurement is made and a 5 cmH
2
O column is in the connecting tubing,
an error of about 5 cmH
2
O may occur.