Calibration — Total Chlorine - Emerson Rosemount 1056 Instruction Manual

Instruction Manual
LIQ-MAN-1056
If the In Process Cal is successful, the screen will return
to the Cal sub-menu.
The adjacent screen may appear if In Zero Cal is unsuc-
cessful. The screen will return to the Amperometric Cal
Menu.
7.6.2 Calibration — Total Chlorine
7.6.2.1 Description
Total chlorine is the sum of free and combined chlorine.
The continuous determination of total chlorine requires
two steps. First, the sample flows into a conditioning
system (TCL) where a pump continuously adds acetic
acid and potassium iodide to the sample. The acid
lowers the pH, which allows total chlorine in the sample
to quantitatively oxidize the iodide in the reagent to
iodine. In the second step, the treated sample flows
to the sensor. The sensor is a membrane-covered
amperometric sensor, whose output is proportional to
the concentration of iodine. Because the concentration
of iodine is proportional to the concentration of total
chlorine, the analyzer can be calibrated to read total
chlorine. Because the sensor really measures iodine,
calibrating the sensor requires exposing it to a solution
containing no iodine (zero standard) and to a solution
containing a known amount of iodine (full-scale standard).
The zero calibration is necessary because the sensor,
even when no iodine is present, generates a small
current called the residual current. The analyzer
compensates for the residual current by subtracting it
from the measured current before converting the result
to a total chlorine value. New sensors require zeroing
before being placed in service, and sensors should be
TABLE 7- 6 Total Chlorine Calibration Routines
Measure Sec.
Total Chlorine
7.6.2.2
7.6.2.3
A detailed flow diagram is provided at the end of Sec. 7 to guide you through the calibration routines.
To calibrate total chlorine:
1. Press the MENU button
2. Select Calibrate. Press ENTER.
3. Select Sensor 1 or Sensor 2 corresponding to
Total Chlorine. Press ENTER.
4. Select Total Chlorine. Press ENTER.
The adjacent screen will appear. To calibrate Total
Chlorine or Temperature, scroll to the desired item and
press ENTER
88
Calibration function: default value
Zero Cal
In Process Cal
S1: 1.234µS/cm
S2: 12.34pH
SN InProcess Cal
Calibration
Error
Press EXIT
zeroed whenever the electrolyte solution is replaced.
The best zero standard is deionized water.
The purpose of the In Process Calibration is to
establish the slope of the calibration curve.
Because stable total chlorine standards do not exist, the
sensor must be calibrated against a test run on a
grab sample of the process liquid. Several manufac-
turers offer portable test kits for this purpose. Observe
the following
precautions when taking and testing the grab sample:
• Take the grab sample from a point as close as
possible to the inlet of the TCL sample conditioning system.
Be sure that taking the sample does not alter the flow
through the TCL.
• Chlorine solutions are unstable. Run the test immedi-
ately after taking the sample. Try to calibrate the sensor
when the chlorine concentration is at the upper end of
the normal operating range.
Note this measurement must be made using the Model
TCL total chlorine sample conditioning system.
THIS SECTION DESCRIBES HOW TO CALIBRATE
THE MODEL 1056 WITH AN ATTACHED TOTAL
C H L O R I N E S E N S O R .
CALIBRATION ROUTINES ARE COVERED.
Description
Zeroing the sensor in solution with zero total chlorine
Standardizing to a sample of known chlorine concentration
S1: 1.234µS/cm
S2: 12.34pH
SN Calibrate?
Total
Temperature
Section 7.0: Calibration
25.0ºC
25.0ºC
T H E F O L L O W I N G
25.0ºC
25.0ºC
Chlorine
April 2017