Hach AF7000 SCM Manuel D'utilisation De Base page 15

Item Name
(6) Menu/Cancel key Show the menu options or exit the menu options.
(7) Set Zero key
(8) Auto/Manual key
Startup
Connect the instrument to power
Burn hazard. The motor surface gets hot. Do not touch.
Plug the power cord into an electrical outlet. The instrument starts automatically.
Validate the installation
1. Set the zero point. Refer to
2. Increase the coagulant dose by 10%. Make sure that the top and bottom values on the display
increase. Wait 5–10 minutes for the full-scale change to complete.
Note: The instrument shows an approximate half-scale change in 20–40 seconds. A full-scale change occurs in
5–10 minutes.
3. Decrease the coagulant dose by 10% of the optimal dose. Make sure that the top and bottom
values on the display decrease. Wait 5–10 minutes for the full-scale change to complete.
4. Set the coagulant dose back to the optimal dose. Wait 5–10 minutes for the full-scale change to
complete.
Operation
Set the zero point
Pre-requisite: Complete a jar test, or take a zeta potential measurement, to find the optimum
coagulant dose. The optimum dose gives the best floc formation and lowest turbidity without excess
coagulant. Set the coagulant pump speed to supply the optimum dose and examine the coagulation.
If necessary, increase or decrease the coagulant pump speed until the optimum dose is supplied.
Push the Set Zero key to set the top display to 0 when the optimum sample-coagulant mixture goes
through the instrument. If the display later shows a positive or negative number, the coagulant
dosage is above or below the optimum setting.
1. Set the optimum coagulant dose in the system.
2. Wait for the dosage change to get to the instrument and a full-scale change to complete through
the instrument (approximately 5–10 minutes).
3. When the reading is stable, push and hold Set Zero for three seconds. The top display shows 0.
Table 3 Display and keypad descriptions (continued)
Description
Push the DOWN arrow to scroll through the menu options.
Set the zero point. The top display changes to "0".
To set the zero point, push and hold Set Zero for 3 seconds. Set the zero point when
the optimum coagulant dose is added and the reading is stable.
Note: Set the zero point again whenever there is a significant change in source water. Significant
changes include seasonal changes such as lake turnover, after a storm or other high turbidity event.
It is important to keep the variation from the zero point very small so that the instrument can make
fine adjustments.
When the optional 4–20 mA PID controller card is installed, push Auto/Manual to
switch between automatic and manual controller mode.
Set the zero point
C A U T I O N
on page 15.
English 15