liquid level control to proportional valve
liquid level control to proportional valve
(OP)
I have an OEM customer that wants to open / close a proportional valve based directly from a liquid level in a tank. We are proposing an ultra sonic level transmitter giving 4-20 into a PLC or converter card with direct PWM 600ma proportional output to valve.
We are proposing the use of a tube to allow the sensor to see a more stable rise / fall of liquid. The liquid is water with small amounts of oil, typically keeped at >15ppm. I quess the basic question is if "US" is best for this app, it sounds like it is. Would you use a plc? Could I get 4-20ma AI with a PWM 0-600ma AO? Would you look for a converter to do this off the shelf since this is all of the logic? Thanks in advance.
We are proposing the use of a tube to allow the sensor to see a more stable rise / fall of liquid. The liquid is water with small amounts of oil, typically keeped at >15ppm. I quess the basic question is if "US" is best for this app, it sounds like it is. Would you use a plc? Could I get 4-20ma AI with a PWM 0-600ma AO? Would you look for a converter to do this off the shelf since this is all of the logic? Thanks in advance.





RE: liquid level control to proportional valve
Barry
RE: liquid level control to proportional valve
A bell is mounted or in some apps lowered into the liquid. Attached is the lowering chain or cable along with a tube which supplies an inert gas or air just enough to cause a slight bubble to be discharged from the bottom of the bell.
Above the surface where the supply of air/gas goes to the bell, a "T" connection is installed. The side open goes to your pressure xducer. The only drawback to this system is that it requires a small amount of air/gas (just enough for a bubble once in a while)at a steady pressure. The output is linear, easy to clean, and simple.
I've used this in a number of liquid apps and it has worked every time.
RE: liquid level control to proportional valve
If you want proportionate control, buy a valve which can directly take 4-20mA input (why to waste a PLC for one valve?) as suggested by Barry. Ultrasonic level transmitters can't take care of foaming.
Regards,
Believe it or not : A Neutrino is so mass less(and electrically neutral) that, a conservative estimate states, it can pass through a 50 light year thick lead block.
RE: liquid level control to proportional valve
LEVEL. TRANSDUCER ANALOG SIGNAL TO A UNIVERSAL
CONTROLLER W/ 1 ANALOG INPUT AND 4-20mA ANALOG OUTPUT
TO YOUR PROPORTIONAL VALVE.ADD AN ALARM OUTPUT FOR
SAFETY. THIS ALARM MAY BE USED TO OVERIDE PROPORTIONAL
CONTROL SIGNAL TO VALVE.
RE: liquid level control to proportional valve
http://www.tpub.com/content/doe/h1013v1/css/h1013v1_127...
for: Linear Variable Differential Transformer (LVDT) details
(it is extremely reliable)
http://www.tpub.com/doeinstrument/instrumentationandcon...
http://www.sec-america.com/Pdf/Ls-c.pdf
http://www.memagazine.org/backissues/aug98/features/flo...
etc. for more info