The Motor Stopped in My Chlorine Analyzer!

Posted by Ray Sullivan on Thu, Sep 28, 2017 @ 02:47 PM

While starting up a new FX-CLv2 chlorine analyzer we sometimes get a call for help from a customer: "I need to return this analyzer. I calibrated, it was running fine, and then the motor stopped. My old FX-1000P didn't do this, what's wrong?"

First we explain the analyzer is working as designed - the No Flow sensor in the measuring cell didn't detect sufficient flow to the measuring cell, so it signaled the processor to turn off the mixing/stirring motor. The buffer feed motor is also turned off during no flow conditions so as not to waste the pH buffer.

no flow sensor FX-CLv2.jpg

 

It also displays a "No Flow X" alarm on the local touch screen display.

No flow alarm FX-CLv2 chlorine analyzer.jpg

 

It also energizes the no flow alarm relay, indicated by the LED, to alert you to the flow interruption via your SCADA or remote monitoring system:

no flow relay FX-CLv2 chlorine analyzer.jpg

 

After hearing this, the customer will usually say that their old analyzer didn't do this, and they'd like the old style instead. Why is this included anyway? Can we bypass this?

The customer is right, the "old" FX-1000P did not have a no flow sensor; when flow was lost, usually due to a bubble blockage, the motor kept running. The customer wouldn't realize there was a problem until......

Without a continuous supply of water the electrode eventually overheats. The measuring electrode expands due to thermal expansion, the gold tube portion of the electrode then cracks or distorts, causing a water leak between the gold tube and copper post on which it's mounted.

This "short circuit" would cause constant, wildly fluctuating residual readings, prompting a tech support call. After a few questions examination of the electrode would confirm it was destroyed and required replacement, costing over $1,000 dollars.

When we started the re-design of our FX-1000p chlorine analyzer to the digital FX-CLv2, we attempted to resolve or avoid as many issues as possible to make the new analyzer as trouble-free as possible.

We included the optical No Flow sensor in the measuring cell to prevent destruction of the measuring electrode. It works as stated above with an interruption in flow; when flow is restored it turns both motors on, resets the no flow alarm, and displays that flow is restored on the touch screen display with the blue water drop and "FLOW" message.

To the question of "can this sensor be bypassed?", the answer is yes, but you'll first need to sign a waiver to confirm that you want this safety device disabled and will be responsible for the cost of a positive measuring electrode replacement, even during the warranty period.

Their "old analyzer" on the same sample stream probably did experience similar blockages; except that without the sensor and alarm present they didn't know it until the residual dropped to near zero (due to the chlorine being consumed at the electrode and not being replaced) or the electrode was damaged.

So why are the blockages occurring for some customers, or only in certain locations? Usually the flow interruption is caused by a collection of air or gas bubbles that block water entry into the measuring cell. Bubbles can be caused by a pump cycling off and on, but this typically occurs when sampling groundwater with entrained gas or air bubbles. We don't usually see this issue with surface water or wet well monitoring. As the water rises from the well or aquifer, it de-pressurizes, any micro-bubbles present expand in size and collect in the port in the lower block that holds the measuring electrode.

The solution is to use the overflow bypass fitting provided with each new system, or to use the fitting in combination with our flow rotometer.

 

Go To The FX-CLv2 Web Page

Tags: flow blockage, air binding, bubbles

Foxcroft Solution For Analyzer Flow Blockage

Posted 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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Tags: bubbles, air binding, flow blockage, chlorine analyzer