False readings on ultrasonic level transmitter
False readings on ultrasonic level transmitter
(OP)
Hello all,
This is my first post here, if there is anything I did not understand from the new member and new posters forums, please correct me.
I am working on a project that is using aqueous waste tanks. These tanks fill with sudsy waste water, and when they are filled enough, the pumps kick in and pump the fluid out. To gauge the tank level, a Ultrasonic Level Transmitter is being used. The problem is that the soapy aqueous solution is fairly sudsy. Sometimes, the level of solution in the tank is fairly low, and there is a lot of suds. The level transmitter reads these suds as actual fluid, and triggers the pumps on. This can be a problem if the tank is actually dry except for the suds.
Does anyone have suggestions for a better device to determine the liquid level in the tank? Or a source of desudsing agents?
Help is appreciated! Thank you,
Aaron
This is my first post here, if there is anything I did not understand from the new member and new posters forums, please correct me.
I am working on a project that is using aqueous waste tanks. These tanks fill with sudsy waste water, and when they are filled enough, the pumps kick in and pump the fluid out. To gauge the tank level, a Ultrasonic Level Transmitter is being used. The problem is that the soapy aqueous solution is fairly sudsy. Sometimes, the level of solution in the tank is fairly low, and there is a lot of suds. The level transmitter reads these suds as actual fluid, and triggers the pumps on. This can be a problem if the tank is actually dry except for the suds.
Does anyone have suggestions for a better device to determine the liquid level in the tank? Or a source of desudsing agents?
Help is appreciated! Thank you,
Aaron





RE: False readings on ultrasonic level transmitter
Whatever you use, mount it in such a way that it's easily replaced from the outside of the tank.
RE: False readings on ultrasonic level transmitter
RE: False readings on ultrasonic level transmitter
Alternatively, junk whatever is reading the analog sensor, and replace it with two relays, the upper one latches the second relay, which is unlatched by the bottom float switch.
RE: False readings on ultrasonic level transmitter
If you can mount an ultrasonic, you can easily mount a submersible. It hangs down into the wet area from the top and needs to reach down to the level from which you want to measure 'zero'. Sometimes people lift it up a couple inches, being willing to sacrifice a true zero reading to keep the crap that collects on the bottom from fouling the sensor.
Foam is typically so light that it doesn't unduly influence the hydrostatic level reading much.
All submersibles that I'm familiar with are loop powered, with a 24Vdc power supply in the loop. Ultrasonics can be either loop powered or active outputs from 4 wire or 3 wire instruments. So you might have to have 24Vdc at 25mA to power a loop powered level transmitter.
Submersibles are used extensively in sewage lift stations and treatment because they work in a dirty, aqueous environment.
pdf file shows a couple different brands.
RE: False readings on ultrasonic level transmitter
RE: False readings on ultrasonic level transmitter
RE: False readings on ultrasonic level transmitter
Yes, pressure is force/area. So any force other than the head pressure (gravity's pull on the water column) will affect the reading because the area of the sensing diaphragm is fixed.
The movment and swirl of liquid is an additional force applied to the sensor diaphragm. Sometimes the force adds, sometimes the force subtracts.
The effect can be extreme when pressure sensors are installed in the flow pipe that pumps out of the bottom of a tank.
The effect can be minimal if the transmitter is located away from direct flows.
But, you described the vessel as a 'tank', so I assume the tank has some fair amount of horizontal area. Is there an accessible location that isn't right next the pump's suction? Remember, it's on a flexible cable that can be run horizontal some distance if needed.
Frequently, in level measurement, a vertical pipe called a still well or a stilling well, is used to quiet the flow around a level sensor (it's used with many technologies, not just head pressure). I've seen still pipes with holes, slits or notches at the bottom. But if it were me, I'd re-locate a submersible.
RE: False readings on ultrasonic level transmitter
Thank you both dan and trueblood!
RE: False readings on ultrasonic level transmitter
RE: False readings on ultrasonic level transmitter
If the ultrasonic was setup for distance (20mA = low elevation level but farthest distance from transducer, 4 mA high elevation level, but closest distance to transducer), then invert the scaling so that it reflects level.
If the ultrasonic was set up for 'level, then make sure the new range matches the old range, if not adjust the range values.
RE: False readings on ultrasonic level transmitter
RE: False readings on ultrasonic level transmitter
We used to use the ulrasonic sensors on some applications, but the dust would really mess with them The radar has been far more robust.
Krohne also makes some units that we like. I think the krohne is a little easier to program. The Siemens is a little less expensive. Krohne may also give away free programming software. Both units can be programmed from a lcd on the unit itself. There are other manufacturers, we just don't have any of them.
Good luck
Joel Olson
RE: False readings on ultrasonic level transmitter
The ultrasonic sensor in the link below from Introtek will measure the liquid level through the bottom of the tank, avoiding all the froth on top. I haven't used one but I remember it from when the rep stopped by our office. Might be worth a look.
Introtek Continuous Level Detection
Doug
RE: False readings on ultrasonic level transmitter
RE: False readings on ultrasonic level transmitter
I can't really speak to the accuracy or reliability of the sensor. I would suggest giving Introtek a call and telling them about your application. They are very willing to customise a sensor to suit your needs.
DOug