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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1 min read

The Blog: How our analyzer works (part 1)

By Michael Brooks on Wed, Aug 29, 2018 @ 10:32 AM

FX-1000p Amperometric Chlorine Analyzer     Foxcroft Equipment & Service Company's Amperometric Chlorine Analyzer's residual reading is determined by measuring the amperage produced by oxidized chlorine in the measuring cell. The amperage level is directly proportional to the level of free chlorine available in the sample stream. When reading total chlorine, the unit is actually reading converted free iodine from potassium iodine that is added to the cell for Total Chlorine readings.

     The cell itself is constructed such that the sample that runs through it does so at a continuous and fixed rate. Any additional flow is allowed to overflow to waste from a drain below the overflow weir. The sample stream runs down though the lower block, where it mixes with vinegar (and Potassium iodide where Total Chlorine is being analyzed), and then flows upward into the measuring cell. Within the cell, the vinegar provides pH buffering to a value of 4.0, and aids in keeping the cell clean. If Potassium Iodide is being used to read Total Chlorine, it chemically converts any free and combined chlorine residuals into free iodine, which is then read as a total chlorine reading. The cell utilizes a mixer and 150 pvc balls to ensure even chemical mix, clean the electrode and consistent readings. Very pure grades of gold and copper are used in the construction of the electrodes to enhance signal strength. Sample flow leaves the cell from the top and runs out a secondary drain to waste.

See part II to follow

Written by: Gavin McCulloch

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3 min read

The blog: Sodium Hypochlorite “Inherently Safe”

By Ray Sullivan on Fri, Apr 29, 2011 @ 03:00 PM

Bleach can release chlorine gas"If there's a hole in a sodium hypochlorite truck, the liquid spills on the ground and there's no big toxic cloud. It's what they call an inherently safe technology."

 I read this in an article recently published by The Times-Picayune about the New Orleans Sewerage and Water Board’s plan to switch from using chlorine gas to sodium hypochlorite as its primary disinfectant. The goal is to reduce the risk of a catastrophic chlorine gas leak in neighborhoods surrounding the plant due to either railroad tankcar accidents or terrorist acts.

Risk reduction, especially for densely populated areas, is a smart move.

But statements like this about sodium hypochlorite, commonly referred to as bleach, just make me cringe.


False sense of security surrounding bleach

I feel uneasy because customers have told me that bleach is safe. I’ve read proclamations that the risk of a chlorine gas leak has been eliminated by switching from chlorine gas to bleach.

It’s not. And it hasn’t.


Bleach contains chlorine, treat it with the respect you give chlorine gas

This isn’t about bashing sodium hypochlorite; we need it to keep our water safe to drink. The point is it contains chlorine and needs to be treated with the respect it deserves; the same respect which is given to elemental chlorine gas.


The statistics don’t lie; you still need a gas detector

Given the number of reported incidents of chlorine gas exposure caused by accidentally mixing sodium hypochlorite and acid, we always recommend that a bleach storage area should include a chlorine gas leak detector. It not only helps protect personnel and equipment, it can also help demonstrate that everything possible was done to limit the consequences of an accident.


Sodium hypochlorite can produce the same chlorine gas that's being eliminated

Sodium hypochlorite’s properties and characteristics require careful consideration to ensure disinfection of the process water and safe usage through proper equipment selection, maintenance, and handling.

  • Sodium hypochlorite degrades over time, which reduces the amount of available chlorine for disinfection and produces undesirable byproducts.
  • Combining bleach with acids can release elemental chlorine gas, the same stuff that’s being eliminated by many treatment plants.
  •  Sodium hypochlorite can be explosive if mixed with many organic compounds, including petroleum products such as oils, fuels and grease.  Other toxic and flammable gases can be generated by improper mixing with other chemicals under certain conditions. 
  •  Under certain conditions, sodium hypochlorite that has dried on rags or clothes can spontaneously combust. Higher concentrations that dry in heated conditions, such as around pump seals, can become ignitable or explosive on impact.1


 Be Informed

There are numerous other hazards that users need to consider for safe operation. The Chlorine Institute has a wealth of knowledge regarding chlorine and sodium hypochlorite, including free brochures available for download. If you use bleach, we urge you to check it out here.

A switch from chlorine gas to bleach can reduce the magnitude of a chlorine gas leak. At the same time it switches the type of risks, which requires care to ensure the liquid is used as safely as possible.

I look forward to hearing your view on the subject.



1. White’s Handbook of Chlorination and Alternative Disinfectants, 5th Edition, Black & Vetch Corporation, Hoboken NJ: John Wiley & Sons, Inc. 2010, P 463

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