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Technical Center "FX-1000p Troubleshooting"
Foxcroft Equipment and Service Co., Inc. 2101 Creek Road Glen Moore, PA 19343 USA 610-942-2888 FAX 610-942-2769
email sales@foxcroft.com
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Troubleshooting "To help you quickly place your Chlorine Analyzer back on-line."
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On initial startup, the inside surface of the copper electrode should be cleaned BEFORE any calibration is done, due to the rapid oxidation that takes place on pure copper.
Al the trimmers used on the analyzer are of the 30-turn variety, so it may take several turns before you get the desired residual setting on the STD (VR-2) trimmer.
The ZERO and STD settings do interact with each other, so adjusting one setting may affect the other. You may have to go back and forth a couple of times between Zero and STD to get the calibration correct.
Water Sample with Contaminates
Make sure the water sample does not contain any oils, or corrosion inhibitors that would coat the inside of the measuring cell, and inhibit the electrical properties of the cell.
Check the sample flow. There should be ample flow, so that there is a constant overflow from both drains, especially the left one, which is the drain from the sample cell. The left drain should flow at about 120 ml per minute. If there is little or no flow from the left drain, check for a blockage in the flow tube, located under the inlet sample weir, sandwiched between the upper and lower blocks.
Check the vinegar feed. The analyzer should us about a gallon of vinegar every 4 1/2 days, on the #14 peristaltic tubing. If you are using the #13 tubing (assuming the sample is within proper pH and total alkalinity limits), you should use a gallon of vinegar in about 13 days. For quick check, pull the end of the tubing off of the input barb and observe the drip from the end of the tube. It should feed a full drop about every 3 to 4 seconds. For a more accurate check, pull the vinegar from a graduated beaker, and time the feed rate.
Check the peristaltic pump. If the occlusion ring on the peristaltic pump is loose, the rollers cannot fully pinch the tubing, which can cause vinegar siphoning (to much buffer) or little to no vinegar feed, depending where the vinegar bottle wall bracket is mounted. This can also happen on units that are several years old that have been subject to more pump head bearing wear, creating a larger gap between the rollers and the occlusion ring.
The tubing is quite resilient and should last for several years. If the tubing develops a flat-spot where it sits in the pump head, and does not feed correctly, try loosening the tubing clamp and occlusion ring to move the flat-spot out of the pump head so that there is a fresh section of tubing in the pump head.
Check of vinegar itself. Sometimes an older bottle of vinegar just doesn't have enough acidity to cut the pH in the cell properly, or it can be contaminated with white algae. First try a fresh bottle of vinegar. Do not refill an existing bottle of vinegar from a new bottle. Use the new bottle, and throw away the old one. If the old one is contaminated with white algae, it will be transferred to the fresh vinegar. If you find white algae in a bottle of vinegar, make sure to dismantle and clean-out the cell block and peristaltic tube, or the algae will be a chronic problem.
For total chlorine readings, check that you added the correct amount of Potassium Iodide (KI) to the vinegar for the range of the analyzer, and that it was freshly mixed. Do not mix the KI and vinegar ahead of time, as it deteriorates quickly. If you are working in ranges of 20 pm and above, where you may need up to 200 grams of KI per gallon, you should be using the second peristaltic pump option. This will allow you to mix the KI with distilled water, and pump it separately.
Dismantle the cell as described in "maintenance center", and clean the inside surface of the copper ring. This is especially important on initial startup, as the copper is 99% pure, and it oxidizes quickly, even after only a few days of shipment to the installation site. A Scotch-Brite pad works best or you can use 100 grit emery cloth, or steel wool pad. Do not us a Brillo or detergent pad. If the analyzer has been in service for some time, and there is a calcium buildup on the copper ring (due to high calcium in the sample water), it can be dissolved with muriatic acid, or simply scrubbed of with sandpaper. If the sample water is oily or greasy, such as in poultry processing waters, you should pre-filter the sample. The oil or grease film on the cell can be cleaned off with most caustic based cleaners. Do not use any that contain chlorine.
While you have the sample cell dismantled, check all the parts including the positive electrode (refer to positive electrode). There should be 150 PVC balls. If you are short a few, it's no a problem, but if it's 100, the cell may not stay clean. Check for damage to the balls and mixer. If the mixer has damage on the tips, the balls are slipping under the mixer. This would indicate that the mixer paddle is set too high on the motor shaft. To set the gap correctly, (see mixer gap adjustment). Do not forget to put the PVC balls back in the cell.
If the mixer has damage on the sides, the balls are slipping between the mixer paddle and the copper ring. This would indicate that the copper ring has reached the end of its useful life, and needs replacement. The copper ring will slowly erode over time (usually several years or more), making the wall of the ring thinner or mottled. Some sample waters are more aggressive than others, and copper ring life-span will vary by location or application. This problem will usually show up initially as the mixer motor jamming, or reversing by itself. It should be attended to before it damages the motor.
While the sample cell is dismantled, check the positive probe (gold). The probe is 24 karat gold, and as such, it is inert. So normally, it will not require any cleaning, other than wiping it off with a cloth. The gold probe should never need replacement, unless it has been physically damaged. If is made of a gold sleeve that is press-fit on an oversized pure copper stub, which is sealed on either end. If the cap is loose, the probe is loose in the mounting hole, or the gold sleeve is loose on the stud, the seal has been broken. Once the seal is broken, sample water gets inside the probe, and creates and electrical reaction within the probe, which show up as erratic readings or wandering calibration. Positive electrodes can only be repaired at the factory.
Check the pH and total alkalinity (TA) of the sample water. If the pH is above 7.5 or the TA is above 50 ppm, you cannot use the #13 peristaltic pump tubing, you must use the #14 tubing. If you are already using the #14 tubing, and have high pH (above 9.0), or high TA (above 150 ppm), or a combination of both, it may require a stronger "pickling vinegar" (10%) or the secondary peristaltic pump option. The pH in the sample cell should be around 4.0. If it is higher than 5.5, the analyzer will probably read sluggishly, or wander. To check for this, you can either take a pH reading of the water coming from the left drain, or just add a few extra drops of vinegar to the sample weir. If the residual reading goes up, there is a pH and/or TA problem. If the reading does not change, it is unlikely that you have a pH or TA problem.
Check for electrical interference. This might include close proximity to heavy electrical equipment such as: variable speed motor drives, cathodic protection systems, computers, radio transmitter, cellular phones, or walkie-talkies. Normally, electrical interference can be solved with good electrical grounding, but some cases may require a different location for the analyzer. Make sure that there isn't interference from equipment located on the wall in the next room, behind the analyzer.
Electronics failure in the analyzer is rare, unless the unit has been hit by lightning, or a power surge. The analyzer has gone through a live "wet-test," before it leaves the factory, so there should not be any initial startup problems, other than general calibration to your sample water. All the trimmers used on the analyzer are 30-turn units, so it may take more adjustment than you think necessary to see a change in calibration. Electronic problems are often improper calibration.
If it appears that there is a electrical problem on initial startup, check the ribbon cable for bent pins on the connectors. This usually happens when the top board is removed for wiring access, and the ribbon cable is hastily or carelessly reconnected after the wiring is done. If you have problems with the 4-20mA signal output, it is a good indication that there is a problem with the ribbon cable.
If you still suspect an electronics problem, try this test: Remove the wires from the sample cell and use the ZERO trimmer as a chlorine residual simulator (you will have to recalibrate after this test). You should be able to run the analyzer up to the maximum value of its range (example 0.00 - 5.00 ppm). Turn the ZERO trimmer counter-clockwise to increase. As you move through the range, the milliamp output follow the readings, and the low and high alarms should activate at the levels they are set for. If you go to a negative reading, rather than positive, the milliamp output will drive to maximum value until you return to a positive reading (unless you have the anti-negative board option). If you leave it set at a specific value, such as 5.00, it should stay there. The reading should not change more than one digit (assuming that you have already ruled-out external electrical interference.)
The STD trimmer is wired in parallel with the coarse span trimmer (VR-3). If either one is already at its minimum value, it will negatively affect the usable range of the other. If you are unsure of how low a trimmer is set, turn it in one direction until you feel a click (or 30 turns, if it does not click), and then turn back 15 full turns. This will put it at mid-range as a starting point for calibration.
A digital voltmeter connected to TP-1 and TP-2 will allow you to check the voltage range of the analyzer. The usable range of the analyzer is always 0.00 - 5.00 volts DC, regardless of the calibrated range. Zero volts is always 0.00 ppm, and 5.00 is always the maximum "span" value of the analyzer. The factory default value is 5.00 ppm. If the analyzer was ordered with a different range, or the unit was re-ranged in the field, the span value on the display will differ.
The ZERO trimmer has a full 30 turn adjustment range. If offsets the voltage of the input signal from the sample cell, so that a proper zero reading can be set. It has a range of -8.8 to +8.8 VDC, as measured with a digital voltmeter on test points TP-1 and TP-2. Turning the trimmer counter-clockwise increased the voltage, and clockwise decreases the voltage (this is exactly opposite of the STD trimmer). The analyzer is never operated in the negative voltage range. If the ZERO trimmer is inadvertently set so that the circuit is operating in a negative voltage range, the resulting analyzer operation will be erratic, or impossible to calibrate. A good indicator of this is when the reading goes negative following a chlorinated sample being fed to the analyzer and after having set the ZERO calibration. Another example is when the milliamp output goes to maximum when the LED display shows a negative number.
The best way to determine if the ZERO trimmer was set incorrectly, is to attach a digital voltmeter to TP-1 and TP-2, as the problem usually won't show properly on the LED display. If the voltmeter reading shows a negative voltage for any point in the normal analyzer range (factory set default is 0.00 to 5.00 ppm), then the zero setting is incorrect.
The best way to set the ZERO trimmer is to turn it fully counter-clockwise, until you hear a click once per revolution, or 30 full turns. This will max-out the display at about 5.50 ppm and show on the voltmeter at about 8.8 VDC. Then turn the trimmer clockwise until the reading falls to 0.00 on the display and/or voltmeter (this may take several turns). |
