Emerson Rosemount 56 - Page 91

Instruction Manual Section 10: Calibration
LIQ-MAN-56 April 2017
Calibration 81
10.6.3 Calibration — Monochloramine
A
monochloramine sensor generates a current directly proportional to the concentration
of monochloramine in the sample. Calibrating the sensor requires exposing it to a solution
containing no monochloramine (zero standard) and to a solution containing a known
amount of monochloramine (full-scale standard). The Zero calibration is necessary because
monochloramine sensors, even when no monochloramine is in the sample, generate a small
current called the residual or zero current. The analyzer compensates for the residual current
by
subtracting it from the measured current before converting the result to a monochloramine
value. New sensors require zeroing before being placed in service, and sensors should be 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 monochloramine standards do not exist, the sensor must be calibrated
against
a test run on a grab sample of the process liquid. Several manufacturers offer portable test
kits
for this purpose.
To calibrate the chlorine sensor, access the Calibration screen by pressing ENTER/MENU from
the main screen, select S1 or S2 Measurement and press ENTER/MENU. Press INFO at any
time to learn more about this procedure.
A yellow screen will appear with detailed
instructions and information.
The following calibration routines are
covered:
1. Zero Cal Zeroing the sensor in solu-
tion with zero total chlorine
2. Grab Cal Standardizing to a sample
of known monochloramine concen-
tration
1. To Zero Calibrate the analyzer with
the sensor attached, follow the step-
by-step procedures displayed on-
screen.
2. To perform a Grab Calibration by Standardizing the sensor, follow the step-by-step pro-
cedures displayed on-screen.