22
72-910-24 Revision H
Blowdown Sample Modes
Timed
In the timed sample mode, the controller will take a sample based on a user defined Interval Time and
Sample Time. The Interval is the time in between the samples, the sample time is the duration of the
sample. When the interval time expires, the sample time begins. If the conductivity is above the set
point at the end of the sample time the blowdown valve will remain open until the conductivity is below
the set point minus the differential. During the sample time the actual real time conductivity is
displayed, during the interval time the last sample is frozen on the screen unless the blowdown relay is
activated by the HOA function. The limit timer can be set to cause the controller to alarm if a
blowdown cycle exceeds the time set by the user. The limit timer will not deactivate the blowdown
valve; it will only provide and alarm indication.
Continuous
In the continuous mode the controller will take a sample continuously If the conductivity exceeds the
set point the blowdown valve will open until the conductivity is below the set point minus the
differential. The limit timer can be set to cause the controller to alarm if a blowdown cycle exceeds the
time set by the user. The limit timer will not deactivate the blowdown valve; it will only provide and
alarm indication.
Sample and Hold
In the sample and hold mode the controller will take a sample based on a user defined Interval Time
and Sample Time. The Interval is the time in between the samples, the sample time is the duration of
the sample. When the interval time expires, the sample time begins. At the end of the sample time,
the blowdown valve is closed for the Hold time. When the hold time expires the controller will enter the
interval time if the conductivity is not over the set point. If the conductivity is above the set point at the
end of the Hold time the blowdown valve will open for the blowdown time and then close the valve for
the hold time this cycle will repeat until the conductivity is below the set point minus the differential at
the end of the hold time. During the sample time and hold times the actual real time conductivity is
displayed, during the interval time the last sample is frozen on the screen unless the blowdown relay is
activated by the HOA function.
Probe Calibration
There are two methods of probe calibration that can be used to calibrate this probe depending on the
blowdown sample mode selected. Calibration should be performed at the conductivity control set
point, manually bring the boiler into control with a hand-held tester before calibrating. This can be done
with either the manual activation of the skimmer line blowdown, or by the bottom blowdown if possible.
If the controller is calibrated at a point more than 1000uS/cm from the control set point it should be
recalibrated after the boiler conductivity is in control.
