I would like to know about the selection of measurement points for control valves
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Dear friends from Sichuan, I’m just starting to work with automation and would like to learn more about how to select the measurement points for control valves – for things like temperature control, pressure control, and flow control. Should transmitters be installed before or after the valve? I know that the choice should be based on the requirements of the process, but for some minor modifications, no drawings are provided by the design agency; if I make a random choice, I’m worried it might affect future regulation of the system. I was wondering if there are any standards or materials available, thank you.
Refer to GB 50093-2013 Code for Construction and Quality Acceptance of Automation Instrumentation Projects
General temperature regulation, pressure regulation, after the transmitter is equipped with a valve； Flow regulation, before the valve is installed on the transmitter
I don’t even know how to answer this question. It’s best to go and read books on automation; by learning some basic knowledge, you will naturally understand it. From the perspective of automated control, in simple terms, it is necessary to determine the parameters that need to be controlled (i.e., the parameters that need to be measured) based on the process requirements. Then, it is important to figure out what pipeline flow rates need to be controlled in order to ensure that the desired parameters meet the process requirements. These are mainly determined by the process engineering department, while the automation control and instrumentation department is responsible for fulfilling the control requirements. Sometimes, the transmitters and control valves for measuring parameters are not necessarily on the same pipeline.
If it is to control the parameters after the control valve, it is better to install it after the control valve; the same holds true in reverse. If it is a flow meter, it is necessary to ensure sufficient straight pipe sections; the longer, the better.
The flow meter is installed in front of the valve; the temperature sensor is generally placed after the valve, while as for pressure, it depends on whether the device is used for feeding or for pressure relief. Of course, you need to clearly know what the function of your valve is in order to determine whether the sensor should be installed before or after the valve.
I agree with #5’s view. The question you’ve asked is too general; different process requirements entail different control requirements as well. What our automation specialists need to do is determine the measurement points for temperature, pressure, flow rate, etc. – and decide how far these points should be located from the control valves, so as not to affect their regulatory performance.
Look for some books on control principles