Custom Search
RECENT POSTS

Saturday, March 10, 2012

Conductance type: Indirect level measurement






  
As the name implies, conductivity level switches operate on the principle of electrical conductivity.

Electrodes located within containers at the point of control make or break contact with the conductive material, thus completing an electrical circuit which operates load contacts for pumps and solenoid valves or performs other control or alarm functions.

The schematic of a heavy-duty switch of this type is shown in figure below. When a source of alternating current is connected to the primary coil, a magnetic flux is set up which induces a voltage in the secondary coil. Current flows in the secondary coil however, only when the rising liquid completes the circuit between the two electrodes. Completion of the secondary coil circuit and the resultant current flow sets up a bucking action in the lower bar of the transformer core. This tends to divert lines of magnetic flux to the core legs and sets up an attraction that moves the armature, closing or opening load contacts.

One pair of contacts connect the secondary circuit to ground when liquid contacts the upper electrode and acts as a holding circuit to maintain the relay in its closed position until the liquid falls below the lower electrode. This holding circuit provides control of the load circuit through the bottom contacts of the relay over any desired range in the liquid level, depending upon the distance between the upper and lower electrodes.

The flow of current through the low energy secondary circuit is very small and varies with the voltage of the secondary coil. The secondary coil is selected to operate over the resistance of the liquid being controlled.

The two-electrode system shown operates a pump to maintain a desired level in a vessel -from a simple on-off action where one electrode and the container complete a circuit via the conductive material to multi-electrode assembly where several switch actions occur at various container levels.

Conductivity switches are economical and have no moving parts in contact with the measure material. Early, heavy-duty designs were used primarily on water applications because of the high energy levels which could result in sparking to produce fires or explosions. However, manufacturers now offer solid-state designs, operating at low energy levels, which can be considered intrinsically safe.

Article Source: Level Measurement by N. Asyiddin (wwwpiyushpanchal2007.mynetworksolutions.com)


0 comments:

Basics of Instrumentation & Control


To view more posts on BASICS : CLICK HERE

Pressure


To view more posts on PRESSURE : CLICK HERE

Flow


To view more posts on FLOW : CLICK HERE

Level


To view more posts on LEVEL : CLICK HERE

Temperature


To view more posts on TEMPERATURE : CLICK HERE

Analytical Instrumentation


To view more posts on Analytical Instrumentation : CLICK HERE
Related Posts Plugin for WordPress, Blogger...

About This Blog

Hai friends…welcome to my blog. This blog is exclusively for instrumentation engineering students which will provide sources for their reference and studies. As you all know Instrumentation is now a fast emerging and developing field in Engineering. This blog has different categories like PLC, SCADA, DCS, Sensors and Transducers, Computer control of process, Industrial Instrumentation, etc.

This blog will also provide an exclusive ‘ASK ME’ section where you can make any queries and share your ideas about instrumentation. The solution for your queries will be given to you by mail from best of my knowledge and reference.

So I wish this blog may be very useful for your studies and reference.

About Me

Keep In Touch

Follow Me!

Online Queries


Popular Posts