Hach pHD sc Analog Differential pH/ORP Sensors Manuel D'utilisation page 18

If the reading is outside of these limits, clean the sensor and change
the salt bridge and standard cell solution.
5. With the multimeter still connected the same way, rinse the sensor
with water and put it in a pH 4 or pH 10 buffer solution. Wait for the
temperature of the sensor and buffer to reach room temperature.
6. Compare the mV reading in the pH 4 or 10 buffer to the reading in
the pH 7 buffer. The reading should differ by approximately 160 mV.
If the difference is less than 160 mV, call technical support.
6.3 Test the ORP sensor
Pre-requisites: 200 mV ORP reference solution, multimeter.
If a calibration fails, first complete the maintenance procedures in
Maintenance on page 16.
1. Put the sensor in a 200 mV reference solution and wait for the
temperature of the sensor and solution to reach room temperature.
2. Disconnect the red, green, yellow and black sensor wires from the
module.
3. Measure the resistance between the yellow and black wires to verify
the operation of the temperature element. The resistance should be
between 250 and 350 ohms at approximately 25 ºC.
If the temperature element is good, reconnect the yellow and black
wires to the module.
4. Measure the DC mV with the multimeter (+) lead connected to the
red wire and the (–) lead connected to the green wire. The reading
should be between 160 and 240 mV.
If the reading is outside of these limits, call technical support.
6.4 Sensor diagnostic and test menu
The sensor diagnostic and test menu shows current and historical
information about the instrument. Refer to
18 English
Table 3. To access the sensor
diagnostic and test menu, push the MENU key and select Sensor Setup,
[Select Sensor], DIAG/TEST.
Table 3 Sensor DIAG/TEST menu
Option Description
MODULE Shows the version and the serial number for
INFORMATION the sensor module.
SENSOR Shows the name and serial number that was
INFORMATION entered by the user.
CAL DAYS Shows the number of days since the last
calibration.
CAL HISTORY Shows a list of and details for each calibration.
RESET CAL Resets the calibration history for the sensor
HISTORY (requires service-level passcode). All previous
calibration data is lost.
SENSOR SIGNALS Shows the current reading in mV, the
impedance of the active and reference
electrodes and the temperature-compensated
impedance. Shows predicted life when Predict
Enable is on.
IMPED STATUS Shows when the impedance of the sensor
(measured every 3 hours) indicates
malfunction. If enabled (recommended), a
warning is shown when the impedance is
outside of normal limits.
PREDICT ENABLE Adds the predicted life of the pH sensor to the
Sensor Signals screen. The Impedance Status
must be enabled and the sensor must have a
2-point calibration for accurate prediction.
When the predicted life has expired, a warning
is shown on the measurement screen.