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5.2 Conductivity
Menu
The conductivity menu provides the following settings: Calibration, Self Test, Unit selection, and
sampling mode setup. Additional settings are also discussed below. Refer to figure 8, Conductivity
Menu Chrt.
Calibrate
To Calibrate the conductivity, use either a hand held meter, or a standard solution, and adjust the controller to
match. Once Calibrate is entered, the unit continuously displays conductivity readings. Press an arrow key to change
the value displayed to match the hand held meter or the buffer solution. You must press
ENTER
to activate the new
calibration. You must press the
EXIT
key to exit calibration. The Bleed output is unaffected until the calibration
menu is exited, so if it was ON when you entered calibration it will stay on until you exit. If you are using
intermittent sampling, the bleed valve will open automatically when you enter the calibrate menu.
Self Test
Press
ENTER
to begin self test. Press any key to stop. Self Test internally simulates a conductivity sensor and
should always give the reading 1000 µS/cm ±100
μ
S/cm. If it does not, there is a problem with the electronics and
the unit should be serviced. If the self-test is in the expected range, and there is a problem calibrating, then the
sensor or its wiring is at fault.
Units
You may choose to display conductivity in µS/cm or in ppm. Press
ENTER
and then use the Up and Down arrows
to change the units. If you change the units, you will be warned to check your settings. This is important. Set points
are not automatically translated from µS/cm to ppm. If you change the units you will need to change your
Blowdown settings.
ppm C.F.
This is the ppm Conversion Factor (or multiplier). This is typically 0.666 but can be changed to accommodate
various requirements.
Press enter to choose Continuous sampling or one of the types of Intermittent sampling. A 'C' at the end of the
display means that sampling is continuous, an 'I' indicates Intermittent sampling, a “T” indicates Intermittent
Sampling with Timed Blowdown, and a “P” indicated Intermittent Sampling with Time Proportional Blowdown.
Continuous
Continuous sampling installations allow the conductivity to be monitored continuously. If the conductivity rises
above the set point, a valve is opened to drop the conductivity. No additional menus related to this blowdown mode
are found in the Conductivity menu.
Sample
Mode C / I
Intermittent
Intermittent sampling installations read the conductivity at set intervals for a given sample duration. If the
conductivity is above the set point, the valve that controls the sampling will stay open until the conductivity falls
below the set point. If the time the valve stays open goes beyond the sample duration, the controller will display
Extend
on the top status line, as well as the amount of time extended. A limit on this amount of time may be
imposed; see Figure 10 Blowdown Menu.
In intermittent sampling mode, once the set point conductivity has been reached, and the valve is closed, the
conductivity will be re-checked after a programmable Hold Time with the valve still closed. If it is still below set
point, the interval between samples will begin. If the conductivity with the valve closed is greater than the set point,
this indicates that flashing may have caused the blowdown to stop prematurely. In this case, the sampling duration
will begin again. This cycle will repeat until the conductivity is below the set point when the valve is closed.
If any type of Intermittent sampling is chosen, the following settings will become available:
Interval
This sets the amount of time between samples. This is set in Hours:Minutes and can be set between 5 minutes and
24 hours.
Duration
This is the length of each sample. This is set in Minutes:Seconds and can be set from 10 seconds to 59 minutes: 59
seconds..
Hold Time
This is the amount of time that the sample will be trapped with the blowdown valve closed. The Hold Time should
be set for the minimum amount of time required for the trapped sample to reach boiler pressure and rise to its
maximum conductivity value. This is set in Minutes:Seconds and can be set from 1 second to 99 minutes: 59
seconds.
If the sample mode is
Intermittent with Timed Blowdown
, then the sampling sequence is a little different. The
controller will open the blowdown valve at the programmed Interval, for the programmed sample Duration. At the
end of the sample duration time, the blowdown valve will close, and the sample will be trapped for the Hold Time.
If the conductivity of trapped sample is greater than the set point, then blowdown valve will open for the amount of
time programmed below:
