Fluke molbox RFM, Руководство по эксплуатации и обслуживанию

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8. GLOSSARY
Page 161 © 1998-2007 DH Instruments, a Fluke Company
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Absolute
As in “absolute pressure”. Pressure expressed relative to vacuum.
BPR Back Pressure Ratio. The ratio of the downstream pressure to the upstream pressure on a
molbloc-S critical flow based molbloc element. The BPR is used to determine whether
Critical Flow conditions exist so that molbloc-S flow measurements are valid.
Critical flow Also known as “sonic flow”. Flow regime where the speed of gas is accelerated to a
velocity equal to the speed of sound under current conditions and the flow rate can be
predicted by measurement of the upstream pressure at the flow restriction (nozzle), the gas
pressure and temperature conditions and the gas properties.
Clean A DISPLAY function in which the second line of the display is blank (clean).
Deviation A DISPLAY function in which the deviation from a target flow value is calculated and
displayed. The value of the difference between the target and the current flow reading.
Differential As in “differential pressure”. Pressure expressed relative to a value other than vacuum or
atmospheric pressure (see absolute and gauge). Frequently refers to the pressure drop
across the molbloc.
Downstream Location of point A relative to point B in a flow system in which point A is at a different
location in the direction of the flow. For example, the downstream molbloc pressure port is
downstream relative to the upstream pressure port because it is at a different location from
the upstream port in the direction of the flow.
DUT Device Under Test. The device being tested or calibrated.
FA (Flow Adder) Flow adder . A value that is added to the measured flow to offset the measured flow value.
FM (Flow Multiplier)
Flow multiplier. A value by which the measured flow is multiplied to change the slope of the
measured flow.
Freeze
A DISPLAY function in which the current flow reading can be captured and displayed by
pressing [ENTER].
Full Mod Calibration
A molbloc calibration option which is valid over a range of operating pressure.
FS Abbreviation of "full scale". The full scale value is the maximum value or the span of a
measurement range. Limits and specifications are often expressed as % FS.
Gauge As in “gauge pressure”. Pressure expressed relative to atmospheric pressure.
Head
The differential pressure developed by differences in height between two points within a
fluid medium.
Hi/Lo
A DISPLAY function in which the highest and lowest flow observed since hi/lo reset are
recorded and displayed.
K Factor A factor representing the relationship between the process gas and a surrogate gas for a
DUT.
Microrange An optional molbox RFM feature which improves flow measurement resolution and
accuracy under 10 % of FS of the molbloc. Includes a low differential RPT and valve to put
the RPT into and out of service.
Operating Pressure
The average pressure at which the molbloc is operated (average of upstream and
downstream pressure) or, if the molbloc pressure is held constant by an upstream or
downstream regulator, the value of the constant pressure.
PA (Pressure Adder) Pressure adder , used in calibration adjustment to offset an RPT.
Perfect Mass Flow Units Volumetrically based mass flow units of measure that assume ideal gas behavior for all
gases (compressibility factor of 1).
PM (Pressure Multiplier) Pressure multiplier , used in calibration to adjust span of an RPT.
Process Gas
The gas for which a device under test is to be characterized or calibrated. The gas that will
actually flow in the device under test when it is used in a process.
PRT
Platinum Resistance Thermometer. The element used in molblocs to measure
temperature.
Psia
Pressure unit “pounds per square inch absolute”. Pressure expressed relative to vacuum.
Psig Pressure unit “pounds per square inch gauge”. Pressure expressed relative to atmospheric
pressure.