7
2750 DryLoc pH/ORP Sensor Electronics
• When the 2750 is powered with 12 to 24 VDC, the 4 to 20 mA loop output is automatically selected.
• Remove approximately 10 mm (0.4 in.) of insulation and tin each conductor before inserting into connectors.
• To add the EasyCal function to the 2750-1, 2750-3 and 2750-4, use the 8050-2 or 8052-2 junction box.
Current Loop with no junction box
Current loop with Junction box
4 to 20 mA Loop Wiring
All 2750 pH/ORP Sensor
Electronics are factory-calibrated for
maximum out-of-the-box accuracy.
Periodic calibration is required to
compensate for electrode aging.
The optional EasyCal feature allows
calibration to be performed local to
the sensor.
EasyCal Procedure:
The
fi
rst step (Reset) is recommended each time an electrode is replaced, but is NOT necessary upon initial installation or periodic
calibration.
In fact, for periodic calibration it is best for the electrode/sensor assembly to remain intact to minimize the possibility of moisture or other
contamination entering the electrical interconnection area. The electrode/sensor connection must remain dry and clean at all times.
1. Reset the 2750 pH/ORP Sensor Electronics to factory calibration: With no electrode connected to the Sensor, press and hold SW1
until the LED (D1) comes on steady then goes off again (approx. 10 seconds). When the LED goes off, release SW1; reset is complete.
2. Connect an electrode to the 2750 pH/ORP Sensor Electronics.
3. If
digital
(S
3
L) output is being used, place SW2 in the “Cal” position. If 4 to 20 mA output is being used, SW2 position is of no
consequence.
4. Place the electrode/sensor assembly into a calibration solution as follows: (If the electrode is “healthy”, then the 2750 will automatically
recognize the solution. The order in which the solutions are used during the calibration procedure is of no consequence).
• For pH calibration, use any two of these international standards: pH 4.0, 7.0 or 10.0 buffer solutions.
(Signet part number 3-0700.390 contains one capsule of each value)
• To produce standards for ORP calibration, mix the chemical Quinhydrone into pH 7.0 and 4.0 buffers to saturation (
⅛
g per 50ml).
• Regardless of the size of the container used for calibration, one inch of solution is adequate to completely submerge the tip of the
electrode.
•
Allow at least 30 seconds for the electrode response to stabilize before calibration.
5. Press and hold SW1 for approximately 8 to 10 seconds. During this time, the LED (D1) will come on steady then go back off.
Release SW1 (If the LED blinks several times rapidly, the calibration was not successful. See the troubleshooting section.)
6. Remove the electrode/sensor assembly from the
fi
rst calibration solution, rinse the electrode with clean water, and place it in a
second solution.
Allow at least 30 seconds for the electrode response to stabilize before calibration.
7. Press and hold SW1 for approximately 8 to 10 seconds. During this time, the LED will come on steady then go back off.
Release SW1. (If the LED blinks several times rapidly, the calibration was not successful. See the troubleshooting section.)
8.
For
digital
(S
3
L) systems ONLY: Return SW2 to the RUN position.
Calibration is complete. Return the system to service.
Calibration
SW1
EasyCal
button
SW2
RUN/CALIBRATE switch for (S
3
L) system
D1
EasyCal Indicator (green LED)
SW1
D1
+
S
-
SW2
Run
Cal
8052-2
8050-2
SW1
D1
SW2
Run
Cal
1
2
3
4
+
S
-
2750-2
Shield
Red
No Connection
Black
White
Power Supply
12 to 24 VDC
+
-
PLC or Recorder
Loop Input
4 to 20 mA
-
+
Optional Earth ground
+
S
-
1
2
3
4
Black
Red
Power Supply
12 to 24 VDC
+
-
PLC or Recorder
Loop Input
4 to 20 mA
-
+
2750-1
1
2
3
4
+
S
-
2750-2
SW1
D1
SW2
Run
Cal
1
2
3
4
+
S
-
8050-2, 8052-2
SW1
D1
+
S
-
SW2
Run
Cal
8050-1, 8052-1
+
S
-
Optional Earth ground
Required Equipment:
•
2750-2 with built-in EasyCal
or
•
Any 2750 with 8050-2 or 8052-2 junction box with EasyCal
• Standard pH buffers (pH 4, 7 or 10)
