Hach Chlorine Sensor, User Manual

Page: 13 / 442

Recalibrate the sensor whenever disconnected from power and removed
from water for more than 15 minutes.
Choosing the calibration method
An initial 2-point calibration, including both zero
3
and slope
(process concentration) measurements, must be done for new or
refurbished sensors.
One or two measurements are required for sensor calibration.
Measurements are made with the chlorine sensor in the flow cell.
When only one measurement is made (1-point calibration), a zero
calibration or a process concentration measurement (grab sample
analysis) is done. A zero calibration can be done chemically by
measuring water with no chlorine or electrically by electronically
removing the calibration offset produced by the gateway
3
. A process
concentration measurement is done chemically by measuring the
chlorine concentration of the process flow with a reference method (grab
sample analysis) and then entering the measured value through the
controller.
When two measurements are made (2-point calibration), the first data
point measured is the zero-point and is determined by doing a zero
calibration either electrically or chemically using the same method as the
1-point calibration
3
. The second data point measured is the process
concentration and is determined by doing a process concentration
measurement (grab sample analysis) using the same method as the 1-
point calibration.
Note: When a chemical zero calibration is done, the instrument automatically does
an electrical zero calibration before the chemical zero calibration and shows both
offsets in the calibration results.
1-point calibration procedure
1. Push the MENU key and select Sensor Setup, Calibrate, Chlorine.
2. Select 1 Point Sample.
3. If the passcode is enabled in the security menu for the controller,
enter the passcode.
4. Select either Zero Cal (zero calibration) or Process Conc (process
concentration calibration).
5. Select the option for the output signal during calibration:
Option Description
ACTIVE The instrument sends the current measured output value
during the calibration procedure.
HOLD The sensor output value is held at the current measured value
during the calibration procedure.
TRANSFER A preset output value is sent during calibration. Refer to the
controller user manual to change the preset value.
6. If Process Conc was selected:
a. Push ENTER .
The measured value is shown.
b. Wait for the value to stabilize and push ENTER
4
to enter a
process flow measurement.
c. Measure the chlorine concentration of the process flow (grab
sample analysis) with an instrument using a reference method
(e.g., DPD). Use the arrow keys to enter the measured value and
push
ENTER .
7. If Zero Cal was selected, select the type of calibration:
Option Description
ELECTRICAL The offset produced by the gateway is removed to set the
zero-point (no sample used).
CHEMICAL Water with no chlorine is measured to set the zero-point.
8. If Electrical was selected, wait for the value to stabilize and push
ENTER
4
to set the zero-point electrically.
3
An electrical zero calibration is recommended. A chemical zero calibration is only recommended if the process flow chlorine concentrations is
routinely lower than 0.5 ppm.
4
If the option for Auto Stab (auto stabilization) is set to Yes in the Calibration Options menu, the screen will advance to the next step automatically.
Refer to
Change the calibration options on page 15.
English 13