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Anonymous Poster

Pressure Transmitter Working principle

11/19/2008 10:55 PM

Dear All,

Please explain me the working principle of Pressure Transmitter.How it transfer the data to control valves to control the pressure based on pressure changes & how it utilises the air for control the valves.

Thanks.

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#1

Re: Pressure Transmitter Working principle

11/20/2008 7:34 AM

Hey, you have several things to ask here.

1. Please explain me the working principle of Pressure Transmitter:

A pressure transmitter senses a pressure and outputs a proportional current signal. THe working principle varies. Some are resistive, some are capacitive, some are piezoelectric, all with an amplifier and filtering circuit attached. You need to consult your sensor documentation to check what's it type and how it works.

2. How it transfer the data to control valves:

By wires, or in some models, wirelessly. That's why that current output is there...

3. to control the pressure based on pressure changes

The sensor itself is not suposed to control the pressure. It just measures it. Some late industrial models have the ability to command equipment, but the sensor measures, and the control circuit commands under a control loop. Like someone sitting in front a manometer with one hand in a valve... "oh the pressure is under the desired value, let me open the valve a little bit... oh too much, so I'll close a little".

4. how it utilises the air for control the valves.

If you're saying your valves use air for control, so there must be a proportional pressure regulator that is receiving the pressure sensor signal, and, inversely, using this current value to proportionally actuate a torque motor that sends more or less air pressure to the valve actuator chamber, so it modulates accordingly. Most industrial valves have this regulator built in, together with the control system.

Sorry if I could not make myself clear, but your question is really vague.

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Anonymous Poster
#5
In reply to #1

Re: Pressure Transmitter Working principle

09/02/2010 12:58 AM

how it is decided to select a presuure transmitter of resistive , capacitive or piezoelectric?

does it depend upon the application for which it is used?

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Power-User

Join Date: Nov 2008
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#2

Re: Pressure Transmitter Working principle

11/21/2008 5:55 AM

I don't know what language "Re: Pressure Transmitter Working principle Replying to Forum Thread by Guest:" is using, but it's unlikely, in my 30 years of experience, he or she will get it. Engineering skills are directly related to communication skills.

Reply Score 1 for Off Topic
Anonymous Poster
#3

Re: Pressure Transmitter Working principle

11/21/2008 10:25 AM

negative and condescending remarks are of no help to anyone (age/title seldom equals wisdom)

1) basically, pressure transmitters/transducers will send out voltage or current (0 to 5 VDC or 4 to 20 mA as an example)

2) a simple PID controller will read this voltage or current - convert this to a pressure (for example .5 VDC=0psig and 4.5 VDC=100 psig) - you program the PID to what you want for example 80 psig - the PID then knows the error

3) the PID then sends out a signal to open or close a valve (for example if the valve opens the pressure will drop) PID will vary its output signal until what you want (80 psig) is what is measured by the pressure transmitter/tranducer

you can play around with the PID constants or get fancy with bode plots/laplace transforms to check for stability - remember, if there are other valves in the system instability might occur (two valves fighting each other over their desired flow/pressure)

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Power-User

Join Date: Nov 2008
Posts: 158
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#4
In reply to #3

Re: Pressure Transmitter Working principle

11/24/2008 4:28 PM

You are so right, so where's the negative part? If I gave you an incorrect electrical formula & your building burned down, would that be of any help? Communication failures have caused jets to nearly crash land (reference the plane that was refueled in Canada in kilograms instead of lbs that had to make an emergency landing on an old airstrip that was being use as dragway for kids racing; reference the sattelite that failed because some engineers didn't do the conversions correctly; reference the Hubble grind angle spec screw-up etc).

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