The factors to consider chapter discusses the economic effect of a process plant will produce a great impact. More and more of the adjusting valve (control valve) the user to concentrate on the dynamic performance parameters, such as a dead zone, in response to the time and the installation of the gain (in the load conditions of the actual process), as a method for improving the performance of the process loop method. Although in the case of an open loop measurement Most of these dynamic performance parameters is possible, but only when the measurement of the closed-loop performance, the impact of these parameters will become clear. Closed-loop test results show the ability of three different valves, the degree of deviation of the reduction process in the different setting conditions.
This figure as a percentage the setpoint variable plotted on a measure of the time constant of the closed-loop - loop tuning process deviation degree. Marked with a horizontal line of the "manual" indicates it does not attempt to control how much the degree of deviation exists when the loop (open loop). Is inclined to the left labeled "minimum degree of deviation of" line represents the calculated ideal valve assembly (nonlinearity) the dynamic performance, all actual valve assembly should normally be located between these two cases.
Not all of the valves provide the same dynamic performance, although they theoretically meet static performance later indicators, and is considered to be almost the valve. Figure 2-7 valve A in the tuning range within a very wide controller follow the line of minimum degree of deviation. The valve exhibited very good dynamic performance, there is a minimum degree of deviation. In contrast, the valves B and C poor performance with the system tuning set faster, in order to reduce the time constant of the closed loop, the degree of deviation increases.
All three valve types are able to control the process and reduce the degree of deviation, but the poor performance of the two. If the performance The the poor valve B is the best performing valve A replacement, and the system is adjusted to the closed-loop time constant of 2.0 seconds, to consider what will happen.
The test data show that this will cause a 1.4% improvement of process deviations. This may not seem like much, but for a long time the result is impressive. Every day, every second a valve that can provide such improvements will be able to save a lot of money in just one year.
Maintaining a more close to the set degree of distribution, it is possible to obtain the set point is moved closer to the place away from the specification limit of the conservation of raw materials. In this example, a 1.4% improvement can be converted into a day, 12,096 U.S. gallons of raw material savings. Assumptions raw material costs of $ 0.25 per gallon, the best valve will directly contribute an additional $ 3,024 a day to profit. Which add up to an impressive $ 1,103,760 a year in savings.
Preferably the excellent performance of the valve in this example provide strong evidence that an extraordinary adjusting valve (control valve) and the component capable of generating a very significant economic effect. This example is only valve able to increase profits through more stringent control. Reduce energy costs, increase output and to reduce the cost of the re-processing of the superscalar product is a good electric control valve (control valve) can increase by more stringent control all of the economic effects. The best regulator valve (control valve), the initial cost may be high, but to spend in the manufacture of sophisticated regulating valve (control valve) on a small amount of additional costs can greatly increase the return on investment. Typically, the initial extra cost of the valve can be compensated within a few days time.
The results of these studies are in the process industry has become increasingly aware of the control valve (control valve) components plays an important role for circuit / device / plant performance. They have also recognized that the traditional designation of a valve assembly, no longer sufficient to ensure that the benefits of the optimization of the process. Like flow capacity, the amount of leakage, such as materials the adaptability and standard performance data and static performance indicators, although it is important, but not sufficient to handle the dynamic characteristics of the process control loop.
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