Welcome back to Foxcroft.com Blog, this is the second part of the blog that was posted on 5/20/11.

      Amplifier board calibration is done at the factory, with a default range of: 0 to 5 ppm. The unit can easily be re-ranged in the field. The analyzer can be ranged anywhere from a low of 0 to 0.5 ppm to a high of 0 to 60 ppm. On-site standardization (chlorine residual calibration) is done when the unit is commissioned, and thereafter needed or desired, using an accurate chlorine residual titrator (or test kit), and chlorinated and non-chlorinated sample of the process waters being analyzed.

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In an effort to conserve water more of our customers are asking about reducing the sample flow rate into their amperometric chlorine residual analyzers.

Discussions with customers sometimes reveal that the sample flow is turned down so far that the water is draining from the sample cell in drops or a trickle.

There are two major problems this causes:

1. The gold positive electrode can be damaged. Water flowing through the sample cell cools the electrode. Without sufficient flow the electrode overheats, deforms, and stops functioning properly.

2. You will get unreliable readings with any amperometric chlorine residual analyzer if a minimum consistent flow isn't maintained because chlorine is consumed at the electrode and must be replaced.

Also bear in mind that to measure the same residual as your process it's important to send the sample to the analyzer as quickly as possible, especially when using the analyzer to control chlorine feed.

To see how the recommended flow from the (left) measuring cell drain should look please check out the video below. A blue "PA Rural Water" pen is placed next to the drain for size reference.

You may notice the overflow from the drain on the right is less than the drain from the measuring cell on the left. That's OK, maintaining the measuring cell drain flow is more important.

For those who prefer numbers, the recommended sample flow into a standard analyzer is 500 ml/min. The minimum sample flow into a standard analyzer is 250 ml/min. The minimum flow rate from the measuring cell drain is 130ml/min.

If you must minimize water usage we recommend using the FX-1000P-RM flow rotometer. With this unit you bypass the overflow weir and feed the sample into the measuring cell. By using the FX-1000P-RM's pressure and flow control, flow into the analyzer can be reduced to 2-1/2 to 3 GPH (157 to 189 ml/min).

Flow consistency is just as important as flow rate. Amperometric chlorine analyzers are flow sensitive. If you reduce the flow to your analyzer and make no other changes to your system the residual will decrease as well.

So if you decide to reduce the flow to your analyzer, don't set it below the minimum recommended flow rate and don't forget to recalibrate!

 Occasionally we encounter flow reduction or blockage in chlorine analyzers monitoring certain groundwater sources.

We examined this problem at a well station in our area that chlorinates and monitors ground water. The water drawn from the sample tap, unlike aerated "white water", was initially clear with some microbubbles of dissolved oxygen or gases.

These microbubbles decompressed and expanded into clusters of larger bubbles to restrict the orifice in the analyzer flow cell. The blockage would trigger a low chlorine alarm and require extra attention from the operators to remain in compliance.

In our research we found that bubble traps or bubble eliminators can provide mixed results in some applications; so we decided to  prevent bubbles from developing within the analyzer.

Our FX-1000P Rotometer keeps the sample pressurized through the flow cell orifice until it reaches the measuring cell. Since the residual is determined almost instantly, the sample overflows to waste before bubbles have time to enlarge and cause problems. 

The controlled flow also eliminates the need to recalibrate due to flow rate changes, which simplifies consistent, accurate chlorine residual measurement. It's easy to install and includes a pressure regulator with gauge.