Electronic Valve Linearization

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- Sean
  
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posted
20 years ago

Wed, Oct 1, 2003 9:32 PM

I am searching for vendors offering electronic valve linearization, and am hoping for suggestions that I haven't been able to find via google searches. Continue reading if you want more details.

An example of an adjustable mechanical cam on a valve would be Maxon's Micro-Ratio valves. I am looking for vendor's that can accomplish a similar thing electronically by mimicing an adjustable cam, i.e. have

10-20 potentiometers or a keypad to enter 10-20 points that would re-scale a 4-20mA signal sent to a valve actuator so that the original signal was linear with respect to flow through the valve. I am searching for solutions less expensive than existing servo parallel positioning systems that cost in the thousands of US$, for example a Honeywell R7999 Fuel Air Ratio Controller. So far my searches via google have turned up several vendors offering electronic linearization, but their offerings are packaged with other electronics (for instance fuel flow totalizers), which I don't want or need. Thanks in advance for any assistance.

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- Patrik Johansson
  
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posted
20 years ago

Thu, Oct 2, 2003 5:30 AM

"Sean" skrev i meddelandet news: snipped-for-privacy@posting.google.com...

Metso automation, former neles control have a positioner called ND800 witch have the function you want. The positioner can be adjusted via a program valled valve manager and a pc.

Regards, Patrik Johansson

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- Michael Hemmer
  
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posted
20 years ago

Thu, Oct 2, 2003 10:59 AM

This is not feasible without flow measurement - which is probably not quite what you're looking for. What I suspect, and what Patrik Johansson already implied in his reply, is that you actually want to establish a linear relationship between the current mA signal and the valve's flow

*coefficient* (Cv) at the respective opening. (Actual flow through the valve, however, depends on other factors as well, e.g. upstream pressure.)

Many, if not most, electronic valve positioners - including those of the company I'm working with, of course ;-) - allow this kind of linearization by means of built-in characteristics. With the default linear positioner characteristic, the process controller (PLC, DCS) gets the actual valve characteristic "handed through" unchanged. With equal percentage and inverse equal percentage positioner characteristics, respectively, a linear valve characteristic can be "changed" to an equal percentage one and vice versa.

In addition to this set of predefined curves, (next to) free-form characteristics can be programmed in most of those positioners. Typically there are eleven pairs of input (e.g., mA) and valve travel values that can be adjusted so as to compensate for a valve's irregular, neither-fish-nor-flesh characteristic (more likely to be found in rotary valves than in globe-style valves). Input values usually don't have to be even-spaced, so the positioner characteristic can be "fine-tuned" in a region that needs it most. However, since the setup procedure involves quite a few keypresses, manufacturers often choose to make this feature available only from the configuration software, not from the front panel (as is the case for the type mentioned by Patrik). The potentiometer approach would probably somewhat too hardware and labor intensive...

Michael