Basics of industrial level measurements 2

Level measurement basics in industries is a vast topic, and we have seen in the previous article some of the most basic level measuring techniques. There are many more which will be unfolded in the coming weeks. Just to have a glimpse, we have differential and head pressure measurement, ultrasonic, Guided wave radar, paddle switches, vibratory forks, displacer and floats and many more just to mention a few.

Here we will first see direct float measurement, most primitive but still widely used level indicating technique used in open tanks mostly, but also employed in closed tank level measurement as well. It mainly consists of a float which has a thin wire attached to it which passes through a couple of pulleys and is attached to an equivalent weight indicator sliding past a scale.

A very simple, but quite reliable method for the measurement of level in a tank or vessel used for a long long time. There are some automated versions which either use a servo to balance the float and in turn measure the amount of turns in terms of level measurement which being an electrical signal can be transmitted to remote locations for measurement and control. Or the pulleys are used with encoders which again can transmit the proportional signals for remote monitoring etc.

There are so many variations in this measurement technique that each and every one of them cannot be discussed here separately. However one important level indication technique used for non contact type measurement is the magnetic level indicator. There is a float of magnetic material usually coated to protect corrosion inside the level troll (chamber) annexed with the tank and outside a strip of small magnetic bi-color flaps or balls which will turn fro one color to another as the float passes by and reset when float passes in other direction .

Simple floats are also used to control levels, a very common example is the flushing tanks in our toilets. As the level drops, the float operated valve starts filling water until the desired level is reached and then it stops the in flow of water. Similar float switches are used in industry to trigger alarms, or control level as well, though the material and construction is different than that used in domestic applications. There are top mounted or side mounted level switches mostly coupled magnetically. In older versions, there were mercury bulbs, which have now been replaced with snap switches or micro switches to indicate if the liquid is above certain level or not. The switching action is then transmitted electrically for control (start or stop a pump) or alarm purpose etc.

Similarly switches are used for both high level detection in a chamber, vessel or tank OR to detect low levels, OR are placed at some strategic location in a tank or vessel to alert the operator or to take an action if required to initiate an alarm or trip.

The installation of a float can be direct immersion in the tank as seen in the first figure, or separate chambers second figure, with isolation valves are also used more commonly for the ease of maintenance or repair. These chambers are mostly coupled with the main vessel or tank through flanged connections though is some cases are directly welded as well.

As we have seen so far, floats are used as indicators as well as switching devices in many cases. Many versions, variations and configurations exist for the float switches. Similarly the float can be a spherical, capsuled or in other shapes. The material of construction also varies to have compatibility with the type of liquid it is used for. However in level measurement sometimes an other item, displacers are used. These, in contrast to floats which are floating or acting on liquid surfaces are immersed in the liquid. This topic we will be covering in our next article.

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(Please note that though the accuracy of the information provided here is based not only on reliable sources, but also based on personal experiences, but it is for providing a general picture and the author is not liable for any loss or damages arising from the use of this information in any instance)