Dwyer TFP-GV - Manual (Page 14)

F-20-TFP-G, pg. 14 of 27
For example, if the unit is calibrated for AIR but the user wants to measure
the flow of Carbon Dioxide (CO
2
) with a specific gravity of 1.517 the flow
reading correction factor would be calculated as follows:
S
new
= Specific gravity of CO
2
= 1.517
S
current
= Specific gravity of Air = 1.000
C
f
= (S
current
÷ S
new
)
0.3
C
f
= ( 1.000 ÷ 1.517 )
0.3
C
f
= 0.88
If the unit has a flow reading of 200ml/min then the corrected flow reading
(for CO2) would be:
Corrected Flow = 200 X 0.88 = 176 ml/min
CAUTION : The use of correction factors can be subject to
inaccuracy and errors of up to ±10%. Please contact Dwyer
Customer Service if accurate, certified recalibration is required.
Calculating a correction factor for a gas enables the calibration of the unit
to be adjusted for that gas. This is accomplished by:
i) Calculate the corrected flow reading or VDC output at 100% of
flow using the above formulas.
ii) Adjust the flow of (the new) gas to give this flow reading
iii) Maintain this flow and ensure a stable reading.
iv) Adjust the gain potentiometer on the unit so that a 5VDC output is
obtained. The unit is now calibrated for the new gas.
For example: A 2.0 -10.0 l/min unit that has been calibrated for Air is to be
used with CO
2
. The correction factor, calculated as above, is 0.88. When
flowing CO
2
the unit will read high i.e. at 5VDC the flow of CO
2
would
actually be 8.8 l/min and not 10 L/min. A flow of 10 l/min of CO
2
through
the unit would give a reading of 10/0.88 = 11.36 l/min or 5.68 VDC on
the unit. Flow should be adjusted so that an output of 5.68VDC or reading
of 11.36l/min is obtained. The gain potentiometer is then adjusted so that
the voltage output becomes 5VDC or the display reads 10l/min. The unit
has now been adjusted for CO
2
and no further corrections to flow readings
are required (if flowing CO
2
).