Tank Truck Low Level Detection


Thread Starter

D Berg

I am looking for a way to determine the low level in a tank truck. Something along the lines of a capacitive prox switch that can be attached to the side of the tanker by the driver. He then starts starts the unload process and the switch would shut off the system. I am assuming the tanker would be metal, the product inside has a density a little more than water. We are also using nitrogen to push the product out of the truck and into the holding tank.
http://www.almegcontrols.com/ can supply either capacitance switch type. You have to watch the cap with temperature variance. The most cost effective is a screw in from the top. Many containers use the Almeg drop in but since you are under pressure the thread in would be best. A 9V batter would run the signal to the pump area.

We assume this is not a permanent installation - as you move it from tank to tank at the drop location. Almeg does not supply the external type. I believe you need a sensor on both sides for that to work.

Bob Hogg

Robert Scott

If the tank is metal and if your sensor is restricted to the outside of the tank, then the metal will shield any capacitive prox switch. Must the sensor be non-invasive? If so, then consider something accoustic. It won't be very accurate though. If you are planing on unloading to the point of being completely empty, then perhaps it would be easier to sense a sudden change in the nitrogen flow rate, or perhaps you could sense density at the discharge point. But if you want to stop the process just short of empty, then these won't work either. The most accurate sensor would be something that was physically inside the tank.

-Robert Scott
Real-Time Specialties


Could a sensor be placed in the discharge that would detect the change from liquid product to nitrogen?

depending on the material being unloaded, either a liquid flow meter, level sensor, nitrogen sensor, etc. Probably easier and cheaper than trying to detect inside the tank.

--Joe Jansen
Measure the Blanket gas pressure supplied by the nitrogen, use this in calculating your gauge range. Put an inches of water, or Psi(if the nitrogen blanket is a high pressure) switch gauge at the bottom of the tanker, any liquid above the height of the level of the gauge will be read directly in inches of head, or will need to be converted to inches from psi. This could be done pretty easily if you know the specific gravity of the fluid. But alas who cares to do all that calculating more than once, If you did it right the first time and set your swithgauge at the right spot.

Ederson L. Amgarten

I think that a good idea for your application could be use an ultrassonic sensor in the top of tank. You can check the Q45U sensors manufactured by Banner Sensors or another company of sensors. A special attention is needed as the nitrogen pressure. You need to calibrate the low level using the nitrogen pressure. The installation and the calibration is very easy. You can see more informations in the Banner site: www.baneng.com.

Ederson L. Amgarten
Vinhedo, Brazil
[email protected]
Assuming the gas is colder than the liquid, you may want to look for a temperature sensor that detects the original temperature, and then signal on a change in temperature as the liquid is emptied and replaced by the gas. Just an idea?

John Perrotti

If you have an external "site glass" you can use a site glass mount and a capacitive sensor very easily. The device would be fairly portable and can be run from batter power.

Take a look at http://www.gordonproducts.com for more information.

Best regards,

John Perrotti
Sales Manager
Gordon Products
Use a vibrating fork, look at us.endress.com, they have a lot of models, i am sure one would fit in your application. vibrating forks are very reliable and i used the model liquiphant of endress to detect level in a truck tank