Hach Sigma 950, Instrument Manual

Page: 52 / 146

50
Optional Device Installation
7.2 pH Probe
7.2.1 pH Probe Connection
The pH probe consists of five wires, three for the pH probe and two for the temperature
probe. Since the pH probe reading needs to compensate for temperature variation, there
is a temperature probe built into every pH probe.
1. Attach the clear wire to either screw on the terminal strip labeled GLASS.
2. Attach the black wire on the shield of the cable to the REF screw on the other
terminal strip.
3. Attach the red wire to the GND screw on the terminal strip.
4. Attach the green and yellow wires to the screws labeled RTD (Resistance
Temperature Detector).
Note: The green and yellow wires can be attached to either one of the RTD terminal screws
because there is no polarity present.
7.2.2 pH Probe Programming
1. From the Main Menu, select
OPTIONS>ADVANCED OPTIONS>DATALOG.
1. Highlight Select Inputs using the
UP
and
DOWN
keys, then press
SELECT
.
2. Highlight pH using the
UP
and
DOWN
keys, then press
SELECT
.
3. Press
CHANGE CHOICE
to cycle between Logged and Not Logged, then press
ACCEPT
.
4. Enter a logging interval using the numeric keypad, then press
ACCEPT
. Valid logging
intervals are shown on the status bar.
5. Select another channel to configure or press
RETURN
to back up one step. Press the
MAIN MENU
function key to return to the Main Menu.
7.2.3 pH Probe Calibration
Once the pH probe is connected and programmed, calibrate the pH probe. Calibrating
the pH probe requires a thermometer and any two of the following buffer solutions: 4, 7,
or 10 pH. The pH probe is an application sensitive device. When used in harsh
environments, the accuracy and life expectancy of the probe decreases.
Calibrate the pH probe each time they are cleaned or replaced. Regular inspection and
comparison to a hand-held pH meter can help determine the optimum cleaning and
calibration schedule for your application.
1. From the Main Menu, select
OPTIONS > ADVANCED OPTIONS > CALIBRATION > pH.
2. Place the pH probe into the first buffer solution. Press any key to continue.
Table 17 pH Connector Pin Assignments
Pin Signal Description
A +5 V dc
B ground
C reference
D pH/ORP
E 5 V dc
F -RTD