4210 Flow Meter
Section 4 Optional Equipment
4-16
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.
4.10.4 pH Probe Life pH probes are consumable items, meaning that they will even-
tually fail and have to be replaced.
During the life of the probe you will have to clean and recalibrate
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 Specifications
Description Submersible, horizontal-mounting
probe with combination-type elec-
trodes. 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 Junction Double porous junction
Temperature Compensation Performed by software inside the flow
meter. The pH Probe contains an inte-
gral temperature sensor.
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