Calculating Output Variables With Known Input Frequency - Emerson Rosemount 8800D Series Reference Manual

Electronics Verification
May 2016
C.2.5

Calculating output variables with known input frequency

Use the following equations with a known input frequency for verification of a flow rate or
4–20 mA output within a given calibrated range. Select the proper equation depending on
if you are verifying a flow rate, mass flow rate, 4–20 mA output, or special units. Example
calculations starting on
To verify a flow rate
For a given input frequency F (Hz), and K-factor (compensated), find the flow rate Q:
where C
in units of pulses/gallon.
To verify a standard or normal flow rate
To verify a mass flow rate
For a given mass frequency F (Hz), and K-factor (compensated), find the mass flow rate M:
where C is the unit conversion and
where C
To verify a 4–20 mA output
For a given input frequency F (Hz), and K-factor (compensated), find output electrical
current I:


I
=

where C
units), and LRV is the lower range value (user units).
To verify a special units output
For special units, first divide the special unit-conversion factor into the base unit factor C
C = C
20
Electronics Verification
page 169
( ) ⁄ ( × x
Q F Hz K C
=
is the unit conversion
x
(
( ) × (
Q F Hz DensityRatio
=
F
M
= -------------------------
( K ρ ) ⁄ ⋅
C
( ) ⁄ ( )
M F Hz KC x
=
is the unit conversion using density (
x
(
⁄ × ) LRV
F K C
–
× (
x 16
-------------------------------------------------
URV LRV
–
is the unit conversion
x
/special units conversion factor
x
may clarify how these equations are used.
)
(Table C-1 on page 168) and K is the compensated K-factor
)
) ⁄ ( × x )
K C
is density at operating conditions:
ρ
ρ ) (Table C-1 on page

)

4
+

(Table C-1 on page 168), URV is the upper range value (user
(Table C-1 on page
Reference Manual
00809-0100-4004, Rev DC
168).
168).
.
x
167