P/R60 & P/R65 Page 10
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.