Level Sensor for Equipment Protection

[sfardella]

Hi All,

I am designing electrical equipment for a water channel application (flow > 20 MGD) where maintaining a minimum water level is a critical feature of equipment protection. If the channel water level drops below a specified point it is possible that the equipment could be damaged. I am interested to get some feedback from people who have had success with a similar application. Suggestions of what is the most robust design, technology, or safety strategy are welcome.

Best Regards,
sf

 

[GusD]

Hi stardella

If what you're looking for is instrumentation to measure
water level,there are many technologies from non contact
Ultrasonic level TXs ,radar level detectors and the trusted capacitive probes.As for the robusteness it may very well depend on the installation and environmental conditions.We use some of these Technologies on our process to measure tank levels.They are not without problems,the greater the expected measurement precision
the grater the cost and the associated maintenance(clibrations).

GusD

 

[jbartos]

Suggestion: There are various principles of operation of water level sensing. Usually, type of application will decide the principle of operation. In some cases there will be a good choice. Usually, the simplest and most reliable sensing is selected. Various parameters also need to be evaluated, e.g. accuracy, environment, water with ice, debris, etc. There may also be a need for communication. Wireless communication is now applied, as well as solar cell to power the units. There are many aspect of this application. It will be better to narrow it down by providing more info about the application.

 

[whataboutbob]

Hello,
I would suggest an ultrasonic system. Try going to

http://www.omega.com.

They havecomplete level controller / ultrasonic sensors with either analog or relay output for your control. Very rugged and fairly accurate. However ultrasonic sensors do exhibit problems if surface has foam.

 

[sfardella]

Thanks for the feedback. Due to the critical nature of the alarm condition I have determined that ultrasonic level sensing is inappropriate. Ultrasonic is fine for active level monitoring but, in the application that I am concerned with, a point level switch is what is required. The technologies that I have focused on are:

1. Conductive
2. Piezo-electric (frequency shift tuning fork)

The conductive sensing technology is a low-cost, simple technology. The disadvantage is that level detection is dependent upon the resitivity/conductivity of the liquid.

Piezo-electric is higher cost but the sensor operation is independent of the medium, only viscosity is a factor.

Your feedback is welcome regarding any experience with either of these technologies.

Regards,
sf

 

[fernandoelec]

Hi Sfardella,

It depend of your pplication, but if is critically for your equipment, I suggest to you a presure sensor, I have used in appli cations with slurry and hard enviroments, if you have a fluid mixed this is a good option, for example you can use foxboro, ABB or Rosemount devices for that task.

Comment me your results if this work.

Good Luck,

Fernando.

 

[jbartos]

Suggestion: What is so secrete about that water channel application that it cannot be described more in detail to narrow down the variety of flow sensors and their principles?

 

[jbartos]

Suggestion: Visit

http://www.thomasregister.com

and type Sensors: Liquid Level under Product or Service, which will return 273 companies to explore different types of liquid level sensors.
e.g.

http://www.gemssensors.com/

http://content.honeywell.com/sensing/prodinfo/liquidlevel/

etc.

 

[GusD]

Hello Stardelta

It sounds like the measurement of your channel water level is quite critical for whatever you trying to do.
All the Technologies mentioned in the previous posts have great capabilities,however;not a single one of them is immune to "failure".We use all of them and in some cases we overkill the redundacy.2 and 3 level instruments for one vessel.A little too much.
If this is as critical as you suggest, I would install 2 different systems (radar/ultrasonics) or any combination of Capac. probes/Inductive probes or take your pick.As I said ,they all work,but they all fail sometimes.

Being that we are on the subject of level measurements, I have to mention what happen to us a couple of days ago.
We have a level Radar to measure and control the speed of an Apron Feeder in a Hopper.We noticed that the apron feeder motors started slowing down and speeding up for no apparent reason.After a few minutes we happen to notice one Operator had climbed the Ladder to the Radar level and proceeded to start wipping it with a rag.Everytime he made a motion with his hand, the Apron feeder motor acted like it had an empty hopper and motor stopped,he moved the hand and motor sped up.We actually thought it was responding quite fast to the hand movement.
Sometimes we do have a laugh at work.

Thanks for your time

GusD

 

[sfardella]

For those interested in more details of the application: Essentially, we are putting 3kW lamps (enclosed in quartz sleeves) into a wastewater channel - the purpose is to disinfect for bacteria/virus. The lamps rely on the water for cooling and will burn if allowed to operate in air for an extended period of time. So, a reliable level sensor solution is required for equipment protection. One of the challegning features of the application is that the water could be turbulent, foamy, contain algae, have a high or low amount of particulate, etc.

GusD - thanks for the advice. I believe that a redundant solution is appropriate since the equipment is often in a remote location so operator response to an alarm condition could be slow or non-existent. Also, redundancy should help avoid problems that may be due to improper testing or irregular maintenance.


Best regards,
sf

 

[jbartos]

Suggestion to the previous posting: The posted character of water: """the water could be turbulent, foamy, contain algae, have a high or low amount of particulate, etc""" favors your posted level sensor principles and additional ones, e.g.
floating, etc. The turbulence will cause some margin of error for some principles of operation, e.g. piezo-electric. It would be helpful to know the speed of the flow of the upper (surface) water stratum.

 

[PUMPDESIGNER]

Perhaps I am wrong, but I think you are looking for a simple set point type unit capable of one or two set point measurements.

Here are the solutions we have come up with.

TILT SWITCH - Most resistant to serious electrical transients. These used to be mercury but are now made with a rolling ball activating a 5 - 10 amp microswitch. Limitations are vulnerability to debris, requires large space to operate (probably around 20" x 20" x 20" space), Not very accurate, probably around 3-5" difference and large hysteresis. Goulds model A2D33W is an example.

PROXIMITY SENSOR - We are using a Carlo Gavazzi CA18CLN12PA. This is a capacitive proximity sensor. Can go through plastic and sense water without penetration. Reliable, very inexpensive. At present this is what I would use in your situation.

CONDUCTANCE - We are using a Carlo Gavazzi model S196156115 conductance type dual level relay. We make our own probes by simply placing stainless steel carriage bolts through a piece of 1" PVC pipe, attach wires to the threaded bolts inside the pipe, then filling the pipe with potting compount. Also reliable, flexible if you make your own sensors as described, which allows you two set points, hysteresis as you want it, etc.



PUMPDESIGNER