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6.22 Relay (1 – 8) Output Menus – Intermittent (Fixed Blowdown Time) Types
This page is used for boiler control where the conductivity is checked at intervals, and if found to
be above the set point, the relay is activated for a fixed time. The following sequence occurs while
sampling:
The relay activates to open the control valve, allowing a sample of the boiler water to flow past the
electrode. The valve remains open for the time programmed in Duration of Sample.
The relay deactivates, and closes the control valve. The sample is held in the pipe for the time
programmed in Hold Time.
At the end of the hold time, the controller reads the conductivity, and compares it to the set point
value.
If it is above the set point, the relay activates and opens the valve for the time programmed in
Blowdown Time.
The valve closes again and the sample is held again.
If the conductivity is still too high, the blowdown time repeats.
This continues until the conductivity is below the set point.
The valve closes and will not reactivate until the Interval Time has expired.
You may also change the Relay Control Mode here. If you do, you will have to reselect the Input
Assignment as well.
This section assumes that the Relay Control Mode is set to Intermittent (Fixed Blowdown Time).
Other control mode types are described in other sections of the manual.
Relay Control Mode
Click on the arrow of the pull down menu and select the way that you want to control the relay.
See Section 6.2 for details on each control mode.
Relay Input Assignment
Click on the arrow of the pull down menu to select the sensor to be used to activate this relay.
Current Reading
This is a display of the current process value as measured by the assigned sensor.
Status
This displays the current status of the relay output, either “Off” or “On”, and if on, the amount of
time it has been on. Possible status messages are Off, Off/Manual, On/Time counting
down/Sampling, Off/Time counting down/Holding, On/Time counting down/Blowdown, Off/Time
counting down/Waiting and On/Time counting down/Hand (for manual activation). The only
possible error messages are Interlock and Sensor Error. See section 8.1 for a complete description
of error messages.
Custom Name
This menu allows you to call the output another name if desired. Type the new name in the text
box.
Set Point
Type in the desired set point value. The control direction is always Force Lower.