Ultrasonic level transmitter on humid tank


Thread Starter

yongkeun kim

ultrasonic level transmitter is installed on the demiwater tank, hot and humid area.

now the level sensing value is fluctuating. it seems to be caused by due because this plant is located in very hot area (saudi arabia).
when the level instrument is pulled out, plenty of dew is hanging on the sensing area. and after we clean it, sensing gets better but it ends fluctuating few hours later. is there any good solution for this situation? Should ultrasonic level instrument not be chosen on the hot and humid water tank?

warm regards,
such devices should not be used in condensing services without some provision for keeping the transponder components free of condensate.

Moisture on the face of a transducer is a known problem with ultrasonics. The temperature of the air in the tank is below the dewpoint temperature of the relatively moist air over the water so water condenses.

Some people tell me that applying a water repellent spray, like Rain-x, a hydrophobic silicone polymer (according to Wikipedia), will help in disbursing the beads of water.

Another solution I've heard of was using a fan to exhaust the air in a vented water storage tank and replace it with outside air. The outside air wasn't that much warmer but held less moisture so it had a lower relative humidity and a lower dewpoint temperature.

In another case, the moisture problem was so persistent that the ultrasonic was replaced with a submersible pressure transmitter because there was no lower tapping point or flange to connect a DP level transmitter to.
No. You should not be using an ultrasonic level sensor in this application. You probably are seeing "ghost level" readings due to the thermocline above the liquid level, as well as sensor ringing caused by the condensation on the sensor. I would use either a FMCW radar level gauge, which may fail because of the condensate, or a submersible differential pressure sensor. I would probably use the submersible sensor, because it eliminates the condensate problem, unless the fluid in the tank is corrosive.


Walt Boyes, FInstMC, Chartered Measurement and Control Technologist
Life Fellow, International Society of Automation
Editor in Chief, Control and ControlGlobal.com
[email protected]
We had a similar issue with a heated tank (roughly 130 deg. F). Used a radar sensor and heated the radar cone to 150 deg. F to keep condensation from forming. It seemed to work for us.

As long as the radar "antenna" (cone in our case) is hotter than the moist air around the unit, condensate shouldn't be a problem. Of course, there is an upper limit to the temperature before the electronics starts failing.

Russ K