Regarding the tuning of valve positioners
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I would like to ask everyone: when adjusting a valve positioner, for example, if the valve opening is too low – at 25% the opening is already at 0 – then, if one first adjusts the zero point and then adjusts the travel range, will there be any change in the zero point after adjusting the travel range compared to the zero point after the initial adjustment? Is it necessary to adjust it again? If there is a change in the zero point, does that change correspond to the change in the travel range? For instance, if the travel range increases by about 20% compared to its original value, will the zero point also increase by 20% accordingly?
If it is a mechanical positioner, repeated adjustment is 100% necessary. Don’t rush to set the zero and full-scale points; instead, use 10% and 90% of the travel range as the zero and full-scale points. If the zero or full-scale point is not in the correct position, adjust it by an amount equal to half of the over-adjustment error (make adjustments based on actual conditions). Once both 10% and 90% are correct, check the actual zero point and full scale; generally, the difference won’t be significant. After completing the adjustment process, it’s not necessary to look directly at the end where the valve is closed; it’s sufficient to check the 3% or 97% positions. The performance of the valve when it is just opened is poor due to a dead zone, so it’s enough to simply verify whether the valve is indeed closed in the end – there’s no need to worry about what the signal value is when the valve is completely closed. In any case, an 3% signal is sufficient to start the operation; if the signal is below 3%, it can be turned off.
Adjusting the zero point has little impact on the range, and adjusting the range also has little effect on the zero point, though there is still some impact; therefore, it is necessary to make adjustments two or three times.
In other words, if the range increases by 20%, then the zero point will also increase slightly, say by 5%, is that right?
That’s what it means............