The Foxcroft Blog

2 min read

The Blog: How it works (part 2)

By Michael Brooks on Wed, Aug 29, 2018 @ 11:35 AM

 FX-1000p amperometric chlorine analyzer     Welcome back to Blog, this is the second part of the blog that was posted on 5/20/11.

      The cell electrodes are connected to the amplifier section of the electronics, where the low level amperage is boosted and ranged to a usable signal. Specifically, 0 to 5 volts DC. The 0 to 5 VDC is then input to and isolation amplifier, which provides electrical isolation and an electrical safety barrier. The 0 to 5 VDC output of the isolation amplifier is then doubled to 0 to 10 VDC, which is used in the final 3 output stages of the circuit. These are the LED display, the alarm circuit and the 4-20 milliamp DC output signal. The amplifier board is powered by a dual bi-polar regulated DC power supply, which provides two sets of +12 and -12 volts. The LED display provides an instantaneous numerical reading of the chlorine residual in parts per million.The alarm circuit provides two user adjustable alarm level settings that activate two relay outputs, which can be used to control external devices or alarm annunciators. The FX-1000p amperometeric chlorine analyzer has been design with process control applications in mind, and as such, is an excellent choice for use in process control of chlorine residuals in freshwater, wastewater, salt water and food processing.

      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.

     If you would like more information or a quote please click on the following link:

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3 min read

Reagentless Chlorine Sensors Are Not Always Low Maintenance

By Ray Sullivan on Wed, Sep 13, 2017 @ 11:24 AM

Many think reagentless chlorine sensors are always the best tools for online monitoring and control of free or total chlorine residual.

3 electrode Free chlorine sensor 020crop.jpgThey have no moving parts and low consumables cost: just replace the electrolyte every 3-6 months and the membrane cap every year.

With no toxic reagents or buffer solutions, and low maintenance, chlorine sensors seem to be the perfect choice for any water system.

If your water does this to equipment, your "low maintenance" sensor will turn into a cost of ownership nightmare.

Iron in flow cell.jpg  iron in FX-CL-F 011.jpgCalcium in drains 045.jpg

Untreated groundwater with elevated iron, solids or calcium levels clogs the micro porous membrane, preventing chlorine from reaching the electrode. In addition to fouling the electrodes, too much iron will prevent 3-electrode sensors from producing an output.

The sensor shown above needed membrane cleaning and electrolyte replacement every 3 days due to excessive iron levels, resulting in:

  • Inability to use a new SCADA system to control chemical feed.
  • Increased chlorine usage and cost.
  • Higher direct labor maintenance cost, and less time to perform other tasks.
  • Higher consumables cost.

There's a proper tool to do every job. As you wouldn't use a pipe wrench to replace a spark plug, you don't use a reagentless membrane sensor to measure chlorine in dirty water.

We define dirty water as containing any of the following and thereby being unsuitable for membrane covered chlorine sensors:

  • Wastewater
  • Potable water with iron, calcium, manganese, turbidity or total dissolved solids above US EPA Drinking Water Standards
  • Hydrogen Sulfide
  • Corrosion Inhibitors

To avoid selling you something that doesn't work, Foxcroft reviews your application first and recommends the better of two types of instruments that best suit your process.  

Our bare electrode model FX-CLv2 excels in dirty or clean water; and our reagentless chlorine sensor models are for free or total chlorine in filtered, clean water.

Don't assume that the most heavily marketed product is always best for your application. We don't hesitate to recommend probe based systems, if there is a high probability it will work without undue attention and maintenance.


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2 min read

Tech Tip: What Flow Rate Does My Chlorine Analyzer Need?

By Ray Sullivan on Fri, Aug 26, 2011 @ 10:34 AM

Amperometric chlorine analyzers need consistent flowIn 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!


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1 min read

Foxcroft Solution For Analyzer Flow Blockage

By Ray Sullivan on Fri, May 20, 2011 @ 09:39 AM

 rotometer stops air binding4 resized 600Occasionally 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.


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