Calibration of Control Valve

Control Valve is the terminology used to a throttling valve which has the ability, or the gradual changing. Is on-off valve including valve controlled? Yes, but rarely referred to as the control valve. Particularly in view of the control valve to valve that can receive both analog command with a collection of analog signals and digital signals.
Calibration control valve is needed to ensure that the control valve actuation can produce responses as desired by the control system in a process. Actuation response is included in the value of precision, linearity, and also the response time course. Control valve as an actuator in a control loop has an important role in meregulating a process. Meregulating failure in a process abnormality is an indication of a process which, if sustained effect to the shutdown.
There are two kinds of calibration are generally known in the control valve of the Manual Calibration and Auto Calibration.
Manual calibration is calibration using manual input to control valve and as a comparison is the calibration. The core of the calibration is to bring value to actual value. Value of a control valva is opening / opening. Openings in the form of a percentage value. Common sense says that the five-point standard as a benchmark as the opening control valve. 0%, 25%, 50%, 75%, 100%. Calibration activity is to sync valve control inputs in the form of analogue signal (assumed HART) with an opening control valve. Value as a standard 4-20 mA instrumentation stretched to represent the opening of a 4mA, 8mA, 12mA, 16mA, 20mA.
In a control valve known terminology Quick Opening, Linear, Equal Percentage. This term to indicate a relationship between the opening and flow rate. The question that arises is whether when Valve Quick Opening, or Equal Percentage travelnya the opening is not linear with input signal? Fisher people's opinion that the Quick Opening, Linear, and Equal Percentage trim characteristik is already set on the geometry of the valve Cv values. So that the input signal to the opening should always be linear.
But there again the question why it is possible to change the input into the Quick Opening characteristik, Linear, and Equal Percentage with HART Handheld Communicator settings from 375? For what?. So that the generated response signal to be curved or parabolic. I have yet to find a specific answer about it. But the requirement of the process makes it possible to give the character of a parabolic response of a control valve shall be controlled when the process is not linear. Therefore we can conclude that the response of control can also be a quick opening, linear, or equal percentage.
Distance travel is also important things that need to be in calibration. Distance of travel is absolutely mechanical adjustment on the control valve stem. Travel distance is the distance from fully open to fully closed. Fully closed means can not be diadjust but to fully open the valve to give some flexibility to the user to shorten or lengthen the travel. The main reference in the construction phase is that the distance of travel shall be in accordance with the data sheet. If the distance of travel of the control valve will detect the open as the 100% maximum. Suppose you are a distance travelnya control valve 3 ", but in reality is mechanical 4" then the travel value in the calibration phase 4 "is considered 100%, when it should be when referring to the datasheet to travel 3" then the value of opening 4 "is approximately 133%. Therefore it must be really certain that the travel distances are in accordance with the requirements in the datasheet to adjustment on the stem.
Autocalibration can be done using the Fisher 375 Handheld. Select the menu and auto calibration. Automatic valve for menstroke highest postition with full control valve, the value would be regarded as automatic 100% value. Then the valve is fully closed will be looking for value, and the value is 0%. And already calibrated valve.
Initial opening becomes important when tight shut off the main thing. This means that when fully closed 0% control valve must be really tight. How sure? Case for the FC, the first step make sure that when the feedback indicates 0%, then it releases the pressure control valve there is no movement back down again. Or by sending a signal below the minimum value of 4 mA, 3.8 mA for example, the control valve also can not go down again. If control valve has been calibrated, but when delivered 8.3 mA signal control valve is still down more then the value 0% is not fully tight.
Things to consider when doing the calibration is out of control valve in conditions of service. And protection of calibration must be eliminated. Make sure the input characteristics and send to the control valve. After calibration is complete control valve is returned in the condition of in-service.
There was a question from a blogger about how the calibration of the HMI using PLC. This term is known as the Remote Calibration. In this project the remote calibration is generally performed in the Pre-Commissioning phase. HART and fieldbus technology in remote normal calibration performed. There is special software that serves as HART & FF Communicator installed on the HMI that can run a calibration mode. AMS Device Manager software I have ever clay used for the remote control valve calibration. Without additional software it but want to do calibration? Hmm ... I have not ever found a PLC can perform remote calibration without the help of technicians in the field. It means I can never know mengedjust PLC I / P is automatic if there is a problem when the signal is sent 25% (8 mA) was opening valvenya 50%. Other stories like that if such conditions are then sent technicians to the field to ngedjust I / P, because if the case is not adjustmentnya PLC by technicians who did the calibration, but the technician who did the calibration. PLC function there can only send a signal AO.
Does AO dr PLC for opening a percentage as well? Mmm ... that PLC could be defined through the program. Want contrived another percentage or scale that it can be done by the programmer. But normally the output of PID calculation logic iteration is set in the form of MV and this percentage is a control command, also opening the valve unit is the percentage of output signal from the PLC command (input to control valve) are also more fit in the form of percentage.
Air to Close - Air to Open / Fail to Open - Fail to Close
There is a fairly easily understandable explanation from a senior one kumpeni in Jakarta about the concept of FO / FC this. The main principles used for determining the FC / FO is a Control Valve when it occurs on the control valve is fail, then the system is in safe condition (low energy). Low energy of a system must be defined by multi-disciplinary team involving primarily the discipline process. Reasonnya play when there is failure, the system should not overpressure, over the level, over flow etc., but its energy must be getting Decrease and Decrease. Supposing you have a control valve on the inlet pipe which regulates fluid into the vessel, so if there is fail, then you certainly want the flow is stopped so as not to overflow then install a control valve Fail to Close (Air to Open). Example for Fail to Open (Air to Close) is easiest for overpressure protection of a vessel. If the pressure is too high then there must be a discarded gas. If for example the exhaust line should be given control valve then Fail to Open, which means that if the system fails then the control valve to be open and protect the pressure of the overpressure in the vessel. More exactnya must use the expert evaluation process is a process engineer. The key is in the condition of control valve fail, the system should lead not to OVER SECURE.