4230 Flow Meter
Section 4 Optional Equipment
4-17
but Isco recommends facing upstream, as there is a stop
on the sensor carrier that is not effective when the probe
is facing downstream.
• Remember to unscrew the rubber guard cap from the
sensing end of the probe when you install it, or the probe
will be unable to sense the flow stream.
The guard cap is to protect the probe during shipment
and storage and to keep the glass membrane and liquid
junction from drying out. If you remove the probe for
any reason, clean it and replace the cap after filling with
4.0 buffer solution. Never store the probe dry or
without the cap in place.
The Isco amplifier box extends the allowable distance between
the probe and the flow meter. The probe has a 25-foot cable, so
you must mount the amplifier within this distance. The
maximum distance between the amplifier box and the flow meter
is 1,000 feet.
All pH probes are consumable items, meaning that they
will eventually fail and have to be replaced.
During the life of the probe, you will have to clean and recali-
brate it periodically. Grease and debris will interfere with the
probe's ability to measure pH accurately. Grease, particularly,
will coat the end of the probe. Because grease is an insulator, it
will keep the ions from reaching the glass membrane and porous
liquid junction, thus failing to create a voltage potential.
You can consider the pH probe at its end-of-life when you can no
longer calibrate it (after cleaning) to ±0.2 pH with the standard
buffers of 4, 7, and/or 10. Another indication of end-of-life is when
the probe calibrates satisfactorily, but takes too long to stabilize
(more than 10 minutes). Such a probe could not possibly respond
to rapidly-changing pH. If your situation requires fast response,
you might consider end-of-life to be when stabilization time
reaches five minutes.
Table 4-3 pH Probe Technical Specifications
Description: Submersible, horizontal-mounting
probe with combination-type electrodes. Porous
Teflon
®
liquid junction to resist fouling and
coating. Steam-sterilized glass hemi-bulb for
long- term stability.
Size 6" long ×
3
/4 NPT.
Body Material Stainless Steel
pH Range 0 to 14 pH units.
Temperature 32° to 176° F (0° to 80° C).
pH Accuracy ±0.1 pH units over the full range.
pH Electrode Junctions
Type II Double porous junction
Temperature Compensation: Done by software inside the
flow meter. The pH Probe contains an integral temperature
sensor.
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