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Frequently Asked Questions - Level
  • What are the advantages of ultrasonic level measurement and control over other systems?
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    • The single greatest advantage of ultrasonic level sensing is that nothing contacts the media being measured. There is nothing to foul, plug or be disturbed by turbulence. The ultrasonic sensor is typically constructed of chemically resistant materials such as PVC, PVDF and Tefzel, making the exposed part of the ultrasonic unit very resistant to damage from fumes. Also, most ultrasonic level systems incorporate the ability to ignore turbulence and some other factors that might produce false signals. In short, ultrasonic is an excellent and cost-effective choice for your level measurement and control system requirements.
  • What kind of pressure transmitter is best for level control, submersible or In-Line?
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    • Submersible transmitters are most frequently used for wastewater lift stations and water storage tanks that are on or under the ground. This is because it is usually relatively easy to gain access to the tank to install and service a submersible transmitter. The advantage of a submersible unit is that it will always read accurate tank level without being affected by pressures surges caused by pumps or heavy demand.
      In-line pressure transmitters, those that have a standard 1/4" or 1/2" process connection, are most commonly used on elevated water reservoirs or on water systems where direct access to the tank is difficult or undesirable. One of the advantages of the in-line type is that it can easily replace an old unreliable pressure switch control by simply unscrewing the pressure switch and installing the pressure transmitter. The pressure transmitter combined with a low-cost electronic level controller can allow much more accurate control and include high/low level alarms as well.
  • I would like to monitor the level in my water storage tank using a pressure transducer, but the tank is a couple of hundred feet away from the area where I want to mount the display unit. How far can I send a 4-20 mA signal and what wire do I use?
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    • A good rule of thumb for transmitting 4-20 mA signal is 1000 feet using shielded pair, 20- or 22-gauge wire. Beyond that distance, some type of amplifier or re-transmitter is usually needed.
  • Can I use float switches in potable water applications?
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    • Yes. USABlueBook now has available non-mercury float switches that have been tested by a recognized water quality lab to an NSF protocol for potable water use.
  • Do I need normally open or normally closed floats?
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    • Well, that depends on your application. If you are pumping water out of your pit that is a sump application and will require normally open floats. On the other hand if you are pumping water into your pit it will require normally closed floats.
  • What type of float is the best to use?
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    • The Avocado floats are a good general float switch used for signal duty. They are available in suspended and pipe mount in varying lengths. But they are mercury switched, which means they have a stainless steel bulb inside of them that is hermetically sealed. The rocking motion of the mercury from side to side changes the position of the switch. They are available in 2 or 3 wire units, the 3 wire allows you to wire them either normally open or normally closed.
  • What is the difference between a mercury switch and a snap action switch?
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    • Basically the mercury float has a small amount of mercury hermetically sealed in a stainless steel bulb that via a rocking motion signals the switch on/off. The snap action switch has a piece of stainless steel which is put under pressure side to side, causing the unit to arch in the middle. Depending on the amount of force being put on the piece of metal, it will snap either in an up position or down signaling the switch.
  • What is all the fuss about mercury anyway
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    • While mercury is still used today in many applications, many states have enacted legislation due to environmental concerns. If you are not sure you can contact your state regulatory agency for assistance. You must remember mercury float switches are not acceptable for potable water applications. When disposing of mercury floats, you should follow your local codes regarding hazardous materials.
  • I am looking for a submersible transmitter to use in my lift station, what do you suggest?
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    • It all depends on the quality of your influent. It can’t have a lot of rags or greasy build up. If you have a lot of rags in your incoming they get tangled around the cord and then you can have erroneous readings. The same with grease, it will build up on the diaphragm and no amount of pulsing will repel it. In both these cases use ultrasonic or non-contacting. Otherwise a good transducer for mildly turbid waste would be a unit like the KPSI 750 with a diaphragm guard and a pulsating diaphragm.
  • What is the difference between ultrasonic and the radar units?
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    • Ultrasonic is a sound wave which is beamed toward the surface of the medium and bounced back to the control unit. The control unit calculates the time it took for the beam to bounce back and thereby giving you a level measurement. The environmental conditions of the area play a large role in accurate readings, mist, steam, light foam and gas vapors are a few. Radar, however is an actual beam sent out to the surface of the meduim and is not as affected by environmental conditions. So if your application has steam or is located outdoors in foggy condions, radar is the thing for you!
  • Our water level meter ho longer buzzes when contact is made with the water, do we need to buy a new one?
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    • Now that depends first of all, have you gotten is stuck or have you been tugging on it? That is the first thing to try to avoid, if your not sure of the topographical of the inside of your well casing you may not be using the right tool. If the inside of your well casing is rough with calcium, lime or iron deposits and you get the probe stuck on any one of these, tugging will result in only one thing, a loose probe. What I would do is unroll the cable and do a really good visual inspection, if you do not see anything-that is good. Next run your hand up and down the cable and see if you feel any small nicks or cuts in the cable, this means a possible bad wire. Most of the time we find that this is the case, if you have a loose probe you can replace it, otherwise you may send it in for repair.