Basic Valve Control

[CW3]

This is for the I/E gurus. Let's say I have a manifold that has six 2" nozzles. This manifold supplies water to various nozzles in a large pipe to cool steam. I have a temperature sensing device (RTD or thermal couple wire) at each location on the steam pipe so I can measure the skin temperature. What I want to do is this: Take a laptop or dedicated PC and be able to "see" the temperature at each location. Based on the temperature, I'd like to be able to actuate the valve(s) to control the water flow to each location (or have a setpoint and have the system automatically adjust the valve(s)). I'd prefer to utilize electric actuators as opposed to electro-pneaumatic so I don't have to wrestle with an air supply. This system needs to be ablr to be transported from jobsite to jobsite. In basic terms, what components do I need (software & hardware)?

Thanks,

Curtis

 

[ScottyUK]

You've identifed the sensing element and final output - you just need to 'glue' them together. I'd suggest a small PLC would be the most economical method. Siemens and Allen Bradley both have suitable products that are reasonably intuitive to work with. You'll also need programming software and comm cables etc. There are many other manufacturers too - those are two brands I happen to like working with.

For the sensing element I'd choose a thermocouple over an RTD for this application.

Are you aware of the downsides of electric actuators in continuously modulating service, which is what you are describing? Higher wear, continuous stop-start cycling, more maintenance. Air actuators would be a good choice if you can arrange the air supply - most places which use steam for industrial purposes have plant air available.



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One day my ship will come in.
But with my luck, I'll be at the airport!

 

[m777182]

Assuming you already have six RTDs you need six transmitters (or one multiplexing six individual inputs), then you need a six channel A/D converter, a device that will transmit the signals into your PC. It could be a RS232, an USB or in some cases even centronics type. On the PC side you need a software that will read the incomming signals and interpret them as a set of numbers in a spread sheet or within a gaph. Then you need a six channel digital output that will provide signal through the same RS232 or USB or whatever into six relays (in some cases centronics will do).The relays will control the valves,
If you want to control the flow in the sence of feed back system you need instead of six digital outputs six analog outputs usually as a 0-10V signal and six control valves with the same input range.Your software should provide some control action: compare each temperature to a set point and calculate the output signal for the valve.
The system could be transportable to some extent:if you can afford surface measuring RTDs there is no problem; however it will be more difficult with the valves.
Regarding the complexity of hardware, communication software and control algorithms it will be most efficiently to contact a professional supplier.
m777182

 

[CW3]

In this situation, the system would run for approx. 24-48 hours. The manifold is a small skid-mounted unit so the valves would all be in place and I could wire them to a suitable "box" on the skid for easy connect/disconnect/power supply/converter.

I guess plant air, or alternative air supply could be managed if it improves reliability and overall system performance.

I want to start getting the components together so I can get my computer hooked up to a valve and do some "in-my-office" testing and simulation. I have a heating device thermocouple wire. I need to get a valve/actuator, an A/D converter and/or PLC, interconnecting cabling, and some software.

As far as valve/actuator.....I suppose there is a choice of 1/4-turn as in butterfly/ball, or full rotating as in globe/gate..........

I'll look at A/B and Siemens.......

I appreciate all the suggestions I can get. Thanks!

Curtis

 

[JimCasey]

That system you want sounds a lot like a Flowserve Worcester Dataflo system. Electric actuated valves with onboard digital controllers, and a central supervisory unit that can look at each unit and download/upload information.

 

[ilan7]

CW3
My suggestion is a bit different. You can order the valves with temperature sensitive actuator without any electrical or pneumatic supply.
Each valve have a spring balanced and Temperature element with capilaty tube, which is installed at the steam pipe at the point the temperature need to controlled. With the spring at the actuator you adjust the valve set point. Less expensive, no supply need and that's the way it was working some years ago. Valves can be found at Emerson (Fisher) and those how are dealing with steam equipment.
(Same stuff can be done with Electrical temp. Elements, PLC and Valves with Pneumatic or hydraulic actuators - at about 20 times the total price)

 

[ScottyUK]

Hi ilan7,

Do you have a weblink or an Emerson part number for those valves? They sound interesting. I'd not realised they were available as an 'industrial' product, although I'm familiar with the principle.


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One day my ship will come in.
But with my luck, I'll be at the airport!