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Introduction to the Adjustment Method for Valve Positioners
Release time:
2026-04-07 15:22
As an auxiliary device for pneumatic diaphragm control valves, the valve positioner plays a decisive role in the operation of these valves. The quality of positioner calibration directly affects valve performance and, consequently, process production operations. Since positioner calibration is a critical skill that instrumentation technicians must master, proficiency in proper calibration methods not only ensures high-quality adjustments but also significantly reduces workload. However, the commonly used calibration techniques sometimes prove ineffective, making it difficult to achieve accurate valve alignment. Therefore, it is essential to analyze and refine conventional calibration methods to develop a more efficient approach.
The steps of the tuning method commonly used in our daily work are:
a. Position the valve stem at the midpoint of its travel, adjust the positioner so that it forms a 90-degree angle with the feedback lever, and then secure the screw.
b. Set the zero point and span to their respective mid-range positions;
c. Apply a 4 mA DC signal to initiate operation of the control valve, then adjust the zero point to meet the specified requirement;
d. Apply a 20 mA DC signal and verify whether the stroke meets the specified requirement; if not, adjust the span until the requirement is satisfied.
e. Repeat steps c and d until both the zero point and the span meet the requirements.
Under normal circumstances, the zero-adjustment spring operates within its linear range, with a limited range of length variation, and the span-adjustment mechanism is constrained in its mechanical position. Consequently, both the length of the zero-adjustment spring and the amplification factor of the span-adjustment mechanism are subject to limitations. When the control valve’s Kv value is either very large or very small, it becomes impossible to calibrate the positioner using conventional adjustment methods—yet such situations are frequently encountered in practical applications. Therefore, alternative methods must be employed to calibrate valve positioners.
2020-01-19
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