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Participant

Join Date: Apr 2010
Location: Pune, Maharashtra, India
Posts: 2

4-20 mA Signal Control Logic Problem.

12/19/2014 7:42 AM

Dear guys,

I want to modulate burner combustion air control valve & oil control valve parallelly by 4-20 mA signal in one of Forging plant. I cant use PLC, since environment is too dusty. I don't want to take feedback from temperature thermocouple (customer dont want) to control firing rate. furnace operator will vary mA signal manually via push buttons/ tuner mounted on control panel. My boudget is too small.

plz give some good suggestions.

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Power-User
Hobbies - Musician - New Member

Join Date: Dec 2014
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#1

Re: 4-20 mA Signal control logic problem.

12/19/2014 7:48 AM

Use V=IR formula, what's the voltage across the circuit 10Vdc or 5Vdc, from that you'll have to find a potentiometer.

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Guru

Join Date: Nov 2007
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#2

Re: 4-20 mA Signal control logic problem.

12/19/2014 8:53 AM

Precision Digital, Siemens, Emerson Rosemount, ABB, EH and several other companies offer stand alone 4 -20mA controllers in varied DIN sizes.

If you are not going to be using a PV feedback signal, the controller can be programmed then locked so that only the manual function will operate.

All come with setup, installation, and operation instructions.

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Guru

Join Date: Jun 2010
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#3

Re: 4-20 mA Signal Control Logic Problem.

12/19/2014 11:30 AM

If you are planning on simply connecting a 4-20 mA signal to both the air damper and fuel control valve, you are doomed to an inefficient system at best and potentially a dangerous system. Real combustion controls characterize the signal so that the fuel-air ratio remains the same.

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Guru

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#4
In reply to #3

Re: 4-20 mA Signal Control Logic Problem.

12/19/2014 11:49 AM

must have had a preset- sorts of adjustment.

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Guru

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#5

Re: 4-20 mA Signal Control Logic Problem.

12/19/2014 1:24 PM

The term for the device you are looking for is "Manual station". A manual station changes its output according to where the operator sets it.

0% output = 4ma

50% output = 12mA

100% output = 20mA

Honeywell's UDC 2500 1/4 DIN controller can be locked in manual mode to function as manual station.

I hope you have flame safety controls on this burner, for the sake of the operators, owners and investors.

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Participant

Join Date: Mar 2014
Posts: 2
#10
In reply to #5

Re: 4-20 mA Signal Control Logic Problem.

07/29/2015 7:50 AM

Hi,

Please make sure your burner is properly safeguarded!

This simple device which allows a 4-20 mA signal to be set by an operator may help you solve your problem.

Regards,

Heinrich.

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Commentator

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#6

Re: 4-20 mA Signal Control Logic Problem.

12/21/2014 4:50 AM

For the love of all you hold dear do not attempt this until you have answered the following question

  1. How is the existing system controlling the fuel/air ratio? Surely not manually with separate valves. If so that issue must be addressed before even contemplating considering the possibility of doing what the client has asked.
  2. If the oil & air valves are linked mechanically with something like a profile cam then all you need to do is drive that linkage with an actuator controlled by 4-20mamp signal which you can generate from a 24vDC power supply and resistors & a pot to give the operator adjustment.
  3. Am I competent to do this? Not if you are asking this question.
  4. Am I a qualified combustion engineer? Not if you am asking this question.
  5. How am I going to prove that each actuator has arrived at the position I have specified. Not specified in the question.
  6. Have I looked at an existing proprietary burner control box which provides this functionality? Not if you are asking this question.
  7. Why have I not contacted a competent insured & certificated combustion engineer?

Sorry about the rant but I hate to see anyone put themselves and other people in harms way when there is proprietary SIL rated SAFE combustion control equipment on the market. Something like the Seimens LMV system with actuators driven by the control box and independently reporting their position back to the control box with the provision of adjustable valve profiles to generate the correct fuel/sir ratio and the ability to sequence all the burner funcions in a safe manner to allow the burner to lit automatically and have the flame monitored continuously. Give it a 4-20 signal and away you go.

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Guru
Philippines - Member - New Member Engineering Fields - Instrumentation Engineering - New Member Engineering Fields - Control Engineering - Who am I?

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#7
In reply to #6

Re: 4-20 mA Signal Control Logic Problem.

12/23/2014 11:31 PM

Agree.

A boiler is not a simple piece of equipment and there are regulations governing their use as well as the methods for their use.

An automatic controller can do the job 24/7 without getting tired. Asking a human to perform the same job in the same way is unrealistic. Even if the operator is just required to tweak the thing every few minutes or so means the boiler could be going into an unsafe condition with no one around to see it.

regards,

Vulcan

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Guru

Join Date: Feb 2011
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#8
In reply to #7

Re: 4-20 mA Signal Control Logic Problem.

12/28/2014 11:19 AM

Sa ato parekoy, naa pay manual ing ani.

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Member

Join Date: Feb 2015
Posts: 6
#9

Re: 4-20 mA Signal Control Logic Problem.

03/09/2015 4:25 PM

you donĀ“t want to take feedback of what you gonna control?? are you serious?

if you are not or don't have the right skill...let the work for the professionals, somebody could get hurt.

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Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

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#11

Re: 4-20 mA Signal Control Logic Problem.

06/25/2024 7:35 AM

One of the options is to delay it until that changes: <...customer...> with a <...small...boudget...> needs to wait until those with a larger <...boudget...> have had their work done instead. Then, some of the leftovers can then be used for the <...small...boudget...> job and everyone will be happy.

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