Hanna Instruments HI 93703 - Manual (Page 10)

10
* 1 FTU = 1 NTU
• Even though HI93703-11 covers a very
wide range of turbidity values, for very
accurate measurements of samples ex-
ceeding 40 FTU *, Standard Methods re-
quire dilution. In such cases, the correct
amount of HI 93703-0 or turbidity-free
water to be added to the sample can be
calculated as follows:
Vos = 3000 / T
where: Vos = volume of sample (mL) to be
combined with HI 93703-0 to
obtain the final volume of 100 mL.
T = HI 93703 reading (exceeding
40FTU*)
E.g.: HI 93703 reading = 200 FTU *
3000 / 200 = 15 mL (Vos)
15 mL (Vos)+85 mL (HI 93703-0) = 100 mL
At this point, take a sample of this solution
and measure its turbidity.
The correct turbidity value of the original
sample will be:
T
n
x 100 mL / Vos = T
a
where: T
n
= new HI 93703 reading
T
a
= actual turbidity value of the original
sample
E.g. If T
n
= 27 FTU *
T
a
= 27 FTU *x100 mL / 15 mL = 180 FTU *
NOTE: Any sample taken above 1000 FTU will
show out of range by blinking "1000".
15
* 1 FTU = 1 NTU
hours (the sample needs to be kept at room
temperature prior to the analysis).
• To obtain a representative sample, gently,
but thoroughly, mix it before samples are
taken. Do not shake (to prevent air bubbles)
and do not let the sample settle.
• It is recommended to calibrate the meter with
the supplied HI 93703-10 @10 FTU* stan-
dard at least once a month or more frequently
for greater accuracy.
• Before inserting vials into the instrument,
wipe them with HI 93703-70 or a soft, lint-
free tissue. Handle vials so that no finger-
prints get on the areas where light passes
(approx. the bottom 2 cm/1 inch).
If you experience any problems in taking mea-
surements, contact your dealer or the nearest
Hanna Customer Service Center.
SOURCES OF INTERFERENCE
• Presence of floating debris and coarse sedi-
ments which settle out rapidly will give false
readings.
• The infrared light source used for HI 93703-
11 turbidity meter, complies with the ISO
7027 International Standard and can effec-
tively minimize any errors due to colored
dissolved substances. This effect, called
"true color", is a common interference for
most commercially available instruments
operating in the range of visible light.
• Air bubbles and the effect of vibrations that
disturb the surface of the sample may give
false results and should be avoided.
• Dirty glassware could also affect readings
along with scratched or dented vials.