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| 4220 Flow Meter |
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| Section 5 Options and Accessories |
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| The Isco amplifier box extends the allowable distance between | |
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| the probe and the flow meter. The probe has a | |
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| you must mount the amplifier within this distance. The | |
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| maximum distance between the amplifier box and the flow meter | |
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| is 1,000 feet. | |
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| Table | |
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| Description |
| Submersible, |
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| electrodes. Porous Teflon® liquid junction to resist fouling and |
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| coating. |
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| Size |
| 6" long ⋅ 3/4 NPT. |
| Body Material |
| Stainless Steel. |
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| pH Range |
| 0 to 14 pH units. |
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| Temperature |
| 32° to 176° F (0° to 80°C). |
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| pH Accuracy |
| ±0.1 pH units over the full range. |
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| pH Electrode Junctions |
| Double porous junction |
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| Temperature Compensation | Performed by software inside the flow meter. The standard pH | |
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| Probe contains an integral temperature sensor. |
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5.9.3 Storage and | If you remove the pH probe from operation, be careful to keep the | ||
Maintenance of pH | glass sensor bulb wet. Always store the probe with the rubber | ||
Probes | cover screwed completely over the threaded end of the sensor. | ||
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| Exposure to air causes the glass membrane on the sensor bulb to | |
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| dry out. This makes it very slow to respond in solution. Pro- | |
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| longed or repeated dehydration of the bulb will ruin the | |
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| probe. | |
The pH sensitive glass can also become “conditioned” to its envi- ronment, especially when it is continuously exposed to high pH (10 and above) solutions. The glass does have a memory and will respond slowly when exposed to a lower pH solution after having been in a high pH solution for any significant period of time.
Storage of a pH probe in a 4.0 buffer solution is recommended as this has a regenerative effect on the glass and does not put a memory on it. Tap water will work if 4.0 buffer solution is not available. Deionized water is good for quick rinses to clean the element, but not for prolonged storage of an electrode. Con- tinuous exposure of the
The reference electrode is also adversely affected when allowed to dry out. Salt crystals from the electrolyte or precipitates of the solution measured will form salt bridges, either within or on the surfaces of the liquid junction, causing the reference to be less conductive and resulting in a higher reference impedance.
This condition will typically worsen until the unit no longer func- tions. Soaking the reference electrode in a 4.0 pH solution, or tap water if the buffer is not readily available, may bring the ref- erence back to life. Boiling the electrode in 4.0 buffer solution or
