How is the CL17 calibrated?

Document ID

Document ID TE3863

Published Date

Published Date 21/01/2019
Question
How is the CL17 calibrated?
Summary
Calibrating the CL17
Answer

This instrument does not require recalibration unless specified by your regulatory agency for compliance reporting purposes. DPD chemistry is very consistent, so the factory calibration is accurate. Also, the analyser is zeroed during each measurement cycle, so any sample color is blanked out each time. This also helps with any slight discoloration of the sample cell between cleanings.
 
There are two methods of calibration on the CL17:

Calibration on known standards:
The introduction of known standards provides the best accuracy by establishing the zero mg/L reference and the span setting on the instrument. Chlorine free deionized (DI) water and a standard is used.  
 1) Place a container of zero reference water above the analyser with at least two feet of head and plumb the analyser so the sample flow can be shut off and the zero reference water substituted.  Let the analyser run on the zero reference water for at least 10 minutes.
 2) Key in the number 0 and then press the ZERO key.
 3) Prepare a 3 to 5 mg/L chlorine standard and verify the actual value by a lab instrument, preferably by amperometric titration.
 4) Switch the standard for the zero reference and run the instrument for at least 10 minutes.
 5) Enter the value of the standard making sure you use a decimal point, and then press STD.
 6) Remove the standard and restart the sample flow. The analyser is now calibrated.
 
Calibration by comparison:
The comparison method should only be done when the sample chlorine concentration is greater than 3.0 mg/L to assure accuracy over the whole range of measurement. Setting the calibration at lower concentrations may provide accuracy at that point, but it can cause large errors in other portions of the span. 
1) Obtain a grab sample from a location where the chlorine concentration is relatively stable.
2) Perform a laboratory analysis on the grab sample and record the value.
3) In the Setup menu under CAL STD edit the value displayed to match the value from the laboratory analysis and press enter.
4) Press exit to return to normal display mode.
The analyser is now calibrated.

For more detailed information on the calibration procedures for the CL17 please see the user manual.