PART THREE - OPERATION
SECTION 5 - CALIBRATING THE ANALYZER
Accu4™ Low-range Turbidimeter System
Rev. 2-300
52
☞
Filling Sensor
B.
SOLUTION 2:
Dissolve 50.00 grams of reagent-grade
hexamethylenetetramine, (CH
2
)
6
N
4
, in distilled water
and dilute to 500 ml in a volumetric flask.
C. In a flask, mix 50.0 ml of SOLUTION 1 and 50.0 ml
of SOLUTION 2. Let this mixture stabilize for 24
hours at 25
°
C,
±
3
°
C. The resultant mixture is a
4000 NTU stock turbidity suspension. Transfer the
stock suspension to an amber glass (or other UV-
light blocking) bottle for storage. Make dilutions
from this stock suspension. When properly stored,
this stock suspension should remain stable for up
to one year.
3.
Make the standard formazin suspension for calibration:
•
20 NTU Standard Suspension:
Use filtered dilu-
tion water to dilute 10 ml of 4000 NTU stock
suspension to 2000 ml.
•
40 NTU Standard Suspension:
Use filtered dilu-
tion water to dilute 20 ml of 4000 NTU stock
suspension to 2000 ml.
Calibration Tip!
Use only freshly prepared, properly
stored, and carefully measured formazin suspension.
Formazin tends to flocculate over time, causing inaccu-
rate readings. Formazin suspensions must be equally
distributed within the flask. Gently swirl the flask several
times. Do not vigorously shake the flask which could in-
troduce air bubbles that may falsely increase readings.
1.
Recommendation:
Before filling the sensor with a for-
mazin suspension (primary standard), hold the analyzer
analog outputs at their present values or transfer them
to preset values to ensure a safe condition for any con-
nected devices.
A.
Press
MENU key
to display
&21),*85(
7(670$,17
(;,7
.
B.
With the “CALIBRATE” line selected (reverse video),
press
ENTER key
to display
.
