4230 Flow Meter
Section 4 Optional Equipment
4-14
The pH probe connects to a 201 module that plugs into the
Parameter Port on the flow meter. The probe has a 25 ft. (7.6 m)
cable. For greater distances, contact the factory. The maximum
distance between the module and the flow meter is 1,000 ft.
(304.8 m).
Note
Do not connect an Isco pH probe and temperature probe to the
201 module at the same time. The “Temperature Probe” input
on the 201 module is for use ONLY with non-Isco pH probes
that do not have built-in temperature sensing. The Isco pH
probe contains its own integral temperature sensor, which, if
connected in parallel with a separate temperature probe, will
cause erroneous readings.
When the ion-selective electrode and the reference electrode are
connected to a high-impedance voltmeter and submerged in
solution, ions move to the surface of the membrane. The elec-
trical charge on the ions creates a potential difference across the
barrier between the solution and the membrane. This potential,
or voltage difference, is proportional to the activity of the ions in
solution.
The potential, when read by a sensitive voltmeter, translates into
a reading of pH. With an Isco flow meter, the voltage is sent first
to a preamplifier inside the probe to reduce the impedance of the
circuit and improve the signal-to-noise ratio, and then on to the
201 module to allow greater operating distance from the flow
meter. The flow meter determines the pH value and displays it.
4.8.2 pH Probe Calibration The 4230 provides a two- or three-point calibration for the pH
probes with commercially-prepared calibrated buffer solutions.
Calibrations of 4 and 7, 7 and 10 and 4, 7, and 10 are all possible.
For accurate readings you must clean and re-calibrate the probe
on a regular basis. How often you need to do this depends on the
condition of your flow stream.
Flow streams with a high grease content will coat the sensing
surfaces of the probe quickly, clogging them and slowing the
response time or stopping it altogether. Installation in very
greasy flow streams is not recommended.
To calibrate the pH probe with the flow meter, first go to program
Step 1 PROGRAM, SETUP. Select PROGRAM. Step through the
units of measure with the Enter key until you reach the menu
that says pH UNITS - NOT MEASURED, pH. Select pH. You
must do this in step 1 or the pH menu will not appear later. Now
go to step 3. PARAMETER TO ADJUST - NONE, LEVEL, pH.
(Other selections may appear.) Select pH. If the pH menu does
not appear in step 3, go back to step 1 to make sure you have
turned it on. Then the pH selection of calibrations will appear. If
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