Specifications

3. OPERATION
Page 37 © 1998-2007 DH Instruments, a Fluke Company
• User units (uxxx): The u prefix indicates user. This option is designed to
provide support for volumetrically based mass flow units with a reference
temperature other than 0 °C (see Section
3.4.3.3). Volumetrically based
mass flow units preceded with the letter “u” (i.e., uccm, ulm) define
standard
conditions as pressure of 101.325 kPa (14.6959 psia) with the user
specifying the reference temperature. User units take into account the true
compressibility of the flowed gas.
• Perfect units (pxxx): The “p” prefix indicates perfect. This option is
designed to provide support for volumetrically based mass flow units that
assume ideal gas compressibility for all gases. Volumetrically based mass
flow units preceded with the letter “p” (i.e., pccm, plm) assume a gas
compressibility factor of 1 for all gases and define standard conditions as
pressure of 101.325 kPa (14.6959 psia) and temperature of 0 °C (32 °F).
Volumetrically based mass flow units at reference temperatures other than
0 °C (32 °F) can be defined using user units (see Section 3.4.3.3).
In early 1996, SEMI (a semiconductor industry interest group) adopted
standard E12-96, which specifies that perfect units be used for
volumetrically based mass flow units. To comply with the SEMI standard,
pccm should be used rather than sccm. To purchase a copy of the relevant
SEMI standard, contact SEMI at telephone [phone] or email
[e-mail].
3.4.3.3 VOLUMETRICALLY BASED MASS FLOW UNITS AT
VARIOUS REFERENCE TEMPERATURES (UXXX)
Units starting with the letter “u” (user units) are volumetrically based mass flow units
(see Section 3.4.3.3) for which a reference temperature other than 0 °C is desired.
When a user unit is selected, the reference
temperature desired must be specified.
After a user unit is selected, the display is:
Temperature ref?
0ºC
Enter the reference temperature desired for the volumetrically based mass flow
unit selected. The temperature unit can be changed between °C and °F by pressing
[SETUP] and selecting <3tempU> (see Section
3.5.3). The temperature selected
applies to all the user units.
Volumetrically based mass flow units, including user units (uxxx) and perfect
units (pxxx), are discussed further in Section 3.4.3.2.
3.4.3.4 VOLUME FLOW UNITS (VLM)
See Section 3.4.3.1 before using volume flow units. Volume flow is
sometimes referred to as actual flow.