HF scientific DRT-100B Research Turbidimeters - Manual (Page 11)

Page 3 DRT-100B (5/00)
III. MEASUREMENT PROCEDURES
(A) ADJUSTABLE SET POINT ALARM CONTROL
This allows the user to set an alarm where a lamp will be illuminated if the NTU readings should become
larger than the value set. The alarm point is set by placing the three position “ALARM” switch labeled
“SET”, “NORM”, to the “SET” position. The potentiometer behind the face plate next to the “ALARM”
switch is then adjusted until the digital display shows the desired value. The “ALARM” switch is then re-
turned to “NORM”. At anytime, the alarm limit currently set in the instrument may be determined by moving
the “ALARM” switch to the “SET” position and reading the digital display. Placing the switch in the “OFF”
position on PN #20012 will cause the unit to operate just as if the switch were placed in the “NORM” position.
(B) STANDARDIZATION
The Reference Standard supplied with this instrument is a pure liquid sealed in glass. It has a value of 0.02
NTU.
Extreme care should be taken to avoid surface scratches on the Reference Standard cuvette. Scratches, to-
gether with dust or film cause analysis error. The Reference Standard optical surface should be wiped clean
each time it is to be used and it is important to use a lint free wiper such as “Kimwipes”.
If cleanliness of the Reference Standard cuvette is in doubt, wash with detergent rinse several times and polish
with “Kimwipes”. Figure 1 shows the critical measuring area in all measuring containers.
The Reference Standard (Catalog No. 60002) should be replaced at least once per year.
The EPA recommends that cuvettes used for instrument calibration or sample measurement be indexed. For
quick and repeatable indexing of the Reference Standard, an indexing ring and locator pin are included with
this instrument.
When shipped, the white locator pin is installed in the collar ring around the optical well of your turbidimeter.
The indexing ring is included in the accessory kit of this instrument.
To index your Reference Standard, slowly rotate the Reference Standard, at least one complete revolution,
while observing the reading, and locate the position of the lowest reading. Without moving the Reference
Standard, install the indexing ring over the ridged cap of the Reference Standard such that the notch on the ring
aligns with the locator pin.
When standardizing this instrument in the future, simply insert the reference standard and rotate it until the
notch on the indexing ring faces the locator pin. Standardize as per the following instructions. (Please note
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