How is the "fully closed (tight)" technology of the regulating valve implemented in the DCS system?
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This post was last edited by oatobnus on 2010-3-8 21:55 In the DCS system, when the regulating valve is used as the terminal execution device of the regulator output, how is the "fully closed (tight)" function implemented? Are there any special requirements when using traditional or smart valve positioners?
“Is the "Full Guan Yan (tight)" technology invented by the original poster himself? I have never heard of it before. However, I can talk about how the DCS system handles the AO point of the regulating valve. In general, the regulating valve opening in the DCS system is 0-100, corresponding to the output 4-20ma model. The electric valve positioner of the regulating valve corresponds to the 4-20ma signal output 20-100kpa air source to control the pneumatic regulating valve to be fully open or fully closed. In order to ensure that the valve can be closed tightly, the DCS system will give a signal lower than 4ma, so that the closing air source for controlling the pneumatic regulating valve is lower than the standard 20kpa to ensure that the valve is closed tightly. In the Honeywell TPS system, the AO output is 0, the 4ma signal is output, and the AO point output is -6.9. At this time, the output signal is already lower than 4ma. I can't remember the specific amount. I can tell it by measuring it with a multimeter. The AO output in the Yokogawa CS3000 system is 0.01 and the output is 4ma ； AO output is 0, and the output signal at this time is already lower than 4ma. This function can be canceled in the property settings of the click. This function is used by default. To sum up, the "fully closed (tight)" technology is to make the output of the AO point lower than 4ma, so that the pneumatic control valve can be closed tightly. The two systems I have used so far have this design idea. Domestic Hollysys and Zhejiang University Central Control have not found this function. The above are just personal opinions, welcome to exchange.
Personally, I think tight shut-off is a requirement for the regulating valve, not the DCS. As mentioned on the second floor, DCS can output a value lower than the normal 0 valve position, that is, the current signal given is 0mA, not 4mA. Each regulating valve has a leakage level. If it is a tight-shutoff valve, when purchasing, it must be stated that the leakage level is the highest to achieve the tight shut-off effect.
This post was last edited by oatobnus on 2010-3-8 09:16. It’s not clear whether the term “Quan Guan Yan” (tight) is accurate or not, but that’s what it’s called anyway. The original text is Tight Shut Function. I understand that this function is an expansion of the analog output signal range (4mA~20mA). The output current can be less than 4mA or greater than 20mA. This function also plays a certain role in practical applications, but it seems to be only applicable to traditional electro-pneumatic valve positioners, but it works well for new intelligent valve positioners. I don’t know why?
It is not easy to do it from within DCS, which will inevitably cause confusion in signal verification.； It is better to do it on site, pneumatically adjust the air source output pressure, and electrically adjust the torque value.
In addition to the two DCS systems mentioned on the second floor, Yokogawa and Honeywell, which have this function, does the Siemens PCS7 system also have this function?
When the AO point output in the TPS system is -6.9, the signal is 1ma. The intelligent valve positioner will stop working when the signal is lower than 3.5ma. This is also a kind of protection. If the valve is often closed with a signal below 0, the sealing performance will decrease over time.
When using this function, be careful not to use it on a frequency converter. Electrical frequency converters also think there is an error when the signal is too much lower than 4MA and cannot start.
Fully open and fully closed. If you have this function, it’s probably what’s mentioned on the second floor.
Current smart positioners for control valves already have this function, but it needs to be turned on through settings.； Pay attention when designing the system: 1. Either set up the DCS in a manner similar to that on the second floor. At this time, the positioner side needs to adjust the lower limit or upper limit of error judgment or turn off the judgment of current errors. ； 2. Either enable this function on the positioner, and the DCS will normally output 4~20mA. The above is for matching intelligent locators with DCS. For non-intelligent locators, proceed directly to the second floor.
Mainly for valves, such as oxygen valves