Aquametrix P/R60 Differential pH/ORP Sensors User Manual - Manual (Page 12)

P/R60 & P/R65 Page 12
5. TROUBLESHOOTING AND SERVICE
5.1. Checking 5-wire Differential Probes P60 and R60
The probe can be checked by a few simple measurements. Two pH buffer solutions, 7 pH and
either 4 pH or 10 pH, and a multimeter are required. For ORP probes two calibration solutions, 200
and 600 mV, are required. Millivolt solutions may be ±20% of nominal value. Actual value is noted
on the bottle.
5.1.1. P60C pH probes
a) Clean the probe as described in Section 4.1. If the system cannot be calibrated, replace the salt
bridge and 7pH buffer solution as described in 4.2. If the system still can’t be calibrated check the
probe as follows:
b) Disconnect red, green, yellow and black wires at the junction box. If you are not using a junction
box, disconnect at the instrument after shutting off the power.
c) Place the probe in 7 pH buffer. Allow enough time for the temperature of the probe and buffer to
stabilize at room temperature.
d) Measure the resistance between the yellow and black wires to check the probe’s temperature
compensator. The resistance should be between 250 and 350 ohms at 25°C. If the resistance is
within specifications the probes thermistor is functioning correctly.
e) Reconnect the yellow and black wires and restore power to the instrument.
f) Measure the voltage between the red and green wires. If it is not within –50 to +50 millivolts with
the probe in 7 pH buffer, the probe is defective. If the voltage is OK proceed to the next step.
g) Rinse the probe and place it in 4 pH or 10 pH buffer. Allow it to stabilize then check the voltage
again between the red and green wires. If the voltage is between 100 and 230 millivolts (negative in
10 pH buffer, positive in 4 pH buffer) the probe is within specifications.
5.1.2. R60C ORP probes
a) Clean the probe as described in Section 4.1. If the system cannot be calibrated, replace the salt
bridge and 7pH buffer solution as described in 4.2. If the system still can’t be calibrated check the
probe as follows:
b) Disconnect red, green, yellow and black wires at the junction box. If you are not using a junction
box, disconnect at the instrument after shutting off the power.
c) Place the probe in 200 mV solution. Allow enough time for the temperature of the probe and
solution to stabilize at room temperature.
d) Measure the resistance between the yellow and black wires to check the probe’s temperature
compensator. The resistance should be between 250 and 350 ohms at 25°C. If the resistance is
within specifications the probes thermistor is functioning correctly.
e) Reconnect the yellow and black wires and restore power to the instrument.
f) Measure the voltage between the red and green wires. The reading should be between 160 and
240 mV; otherwise, the probe is defective. If the voltage is OK proceed to the next step.
g) Rinse the probe and place it in 600 mV solution. Allow it to stabilize then check the voltage again
between the red and green wires. If the voltage is between 560 and 640 mV, the probe is within
specifications.