Lamp Calibration - Emerson Clarity II Instruction Manual

MODEL CLARITY II

6.5 LAMP CALIBRATION

6.5.1 Purpose
Turbidity is a measure of the amount of light scattered by small particles suspended in a liquid. Turbidity depends
on both the quantity of particles in the sample and the intensity of the light used to make the measurement. In
USEPA-compliant turbidity sensors the light source is a tungsten filament lamp. As the lamp ages, the intensity
gradually drops. This means that the measured turbidity will decrease even though the amount of suspended par-
ticles remained constant. To correct for source drift, a photodiode in the sensor continuously monitors the intensi-
ty of the light source. However, if the lamp intensity gets too low, the correction is no longer valid. When this hap-
pens, the analyzer displays a NeedCal warning message. Calibrating at this point will cause the analyzer to
increase the current supplied to the lamp, thus bringing the intensity into the range where the correction is valid.
For best results and to ensure the measurement meets specifications, the sensor should be calibrated using either
slope or standard calibration. However, if turbidity standards are not available and if an error as much as 5% can
be tolerated, the sensor can be calibrated using lamp calibration.
Lamp calibration is not available and is not needed with ISO-compliant sensors.
6.5.2 Procedure
1. Place the sensor in either the measuring chamber or calibration cup.
C C a a l l i i b b r r a a t t e e
Program Display
Calibrate?
S S e e n n 1 1
Sen2
Calibrate?
S S e e n n s s o o r r
C C a a l l i i b b r r a a t t e e
Enter TSS Data
Slope
Standard
Calibrating
Please wait . . .
Lamp Calibration
Done
Calibration
Error
2. Press the MENU key. The main menu appears. Choose Calibrate.
Hold
3. If the analyzer has dual input choose Sen1 (sensor 1) or Sen2 (sensor 2).
Output
If the analyzer has single input, choose Sensor.
Output
4. Choose Calibrate.
>>
5. Choose Lamp.
Grab
L L a a m m p p
6. This screen appears while the analyzer adjusts the lamp current.
7. If the calibration is successful, the screen at left appears.
8. If the analyzer is unable to adjust the lamp current sufficiently to bring the
lamp intensity into the normal range, the Calibration Error screen
appears. The lamp should be replaced as soon as possible.
9. To return to the main display, press MENU then EXIT.
SECTION 6.0
CALIBRATION
41