Metex 2200P pH Analyzer/Controller - Manual (Page 20)

Model 2200P Page 18
5.6 Control Relay A Relay Off Setpoint
5.6.1 If you have configured the relay to control decreasing pH, the relay off setpoint will
be higher than the relay on setpoint. i.e. the auxiliary device connected to the relay
will increase the pH. If you have configured the instrument to control increasing pH,
the relay off setpoint will be lower than the relay on setpoint. i.e. the auxiliary device
connected to the relay will decrease the pH.
a) Enter the menu by pressing MENU, proceed by pressing MENU until the
RELAY A RELAY OFF LED is illuminated. Now use the arrow keys to make the
display read the desired value. Press ENTER. The display will flash until
ENTER is pressed again to confirm the value.
b) Press RUN, to place the instrument on line, or press MENU for another menu
selection.
5.7 Control Relay B Relay On / Off Setpoints
5.7.1 Control Relay B is configured the same as Relay A. (Refer to Sec. 5.5 / 5.6) As
shipped from the factory, Control Relay B is configured to control increasing pH.
However, you may change the direction of control by changing the position of the
DIP switch. (Refer to Section 4.7)
NOTE: A deadband setting on the wrong side of the setpoint is an invalid entry which will
be indicated by the LED flashing when you return to RUN. To correct, return to the
menu and change the relay setpoints or, if the direction of control is the problem,
change the position of the relevant DIP switch. See 4.7 and 5.6.
5.8 Bi-directional Control
5.9.1 The two control relays can be used for bi-directional control, best explained by an
example. In this example the pH must be maintained between 6.00 and 8.00. One
possible configuration would be as follows:
Control Relay A
• Connect Caustic Pump to NO and COM of Relay A
• Set to Control Decreasing pH Dip Switch #4 Bank S1 “On Position”
• Set Control Relay A Relay On Setpoint at 6.00 pH
• Set Control Relay A Relay Off Setpoint at 6.50 pH
Control Relay B
• Connect Acid Pump to NO and COM of Relay B
• Set to Control Decreasing pH Dip Switch #2 Bank S2 “Off Position”
• Set Control Relay B Relay On Setpoint at 8.00 pH
• Set Control Relay B Relay Off Setpoint at 7.50 pH
With the above configuration Relay A will control the addition of caustic. The caustic
pump will turn on if the pH falls to 6.00 pH and will stay on until the pH rises above
6.50. Relay B will control the acid pump. The acid pump will turn on if the pH rises
to 8.00 pH and will stay on until the pH falls to 7.50. Therefore the pH will always
remain between 6.00 pH and 8.00pH