Aquametrix P/R60 Differential pH/ORP Sensors User Manual - Manual (Page 13)

P/R60 & P/R65 Page 13
5.2. Checking Probes P65 and R65 (4-20 mA output)
a) The operation of the 2-wire, 4-20 mA, probe can be checked by a few simple measurements. Two
pH buffer solutions, 7 pH and either 4 pH or 10 pH, and a dc milliammeter are required.
5.2.1. P65C pH Probe
a) Disconnect the red wire at the instrument or power supply and connect it to the milliammeter (-)
black.
b) Connect the milliammeter (+) red to the instrument or power supply red wire output terminal.
c) Rinse the probe and place it in 7 pH buffer. Allow the temperature of the buffer and probe to
stabilize at room temperature.
d) Check the offset of the probe by reading the milliammeter. The reading should be between 11 and
13 mA. If not the probe is defective. If the offset is OK, note the exact reading and proceed to the
next step.
e) Rinse the probe and place it in 4 pH or 10 pH buffer. Allow the temperature of the probe and buffer
to stabilize at room temperature. Now check the span of the probe by reading the milliammeter. If
the probe is in 4 pH buffer, the reading should be between 2.85 and 3.99 lower than the reading
obtained in (d).
f) If the probe is in 10 pH buffer, the reading should be between 2.85 and 3.99 higher than the reading
obtained in (d).
g) If this test is not satisfied the probe is defective.
h) If you wish to check the temperature compensator proceed to step (f).
i) If the span of the probe drops below 2.85mA than the probe still can be used adjustments will have
to be made to the receiving device to compensate for the low span.
j) To check the operation of the temperature sensor in the probe, heat the buffer used in step (e) with
the probe in it to about 50°C. The milliammeter reading should be within ±0.15 mA of the reading
observed in step (e).
5.2.2. ORP Probes R65
a) Disconnect the red wire at the instrument or power supply and connect it to the milliammeter (-)
black. Connect the milliammeter (+) red to the instrument or power supply red wire output terminal.
b) For a probe with range of –500 to 500 mV (white and green wire open):
1. Rinse the probe and place it in the 200 mV solution. The milliammeter should read between
13.7 and 16.7 mA.
2. Rinse the probe and place it in the 600 mV solution. The meter should read between 19.44
and 23.8 mA.
c) For a probe with range of 0 to 1000 mV: (white and green wire joined):
1. Rinse the probe and place it in the 200 mV solution. The milliammeter should read
between 6.4 and 8.0 mA.
2. Rinse the probe and place it in the 600 mV solution. The meter should read between 12.2
and 15.0 mA.