20 mA<\/td> %100<\/td><\/tr><\/tbody><\/table><\/figure>\n\nThe valve position is observed at these values.<\/p>\n\n
If the positioner and valve are mechanically suitable, the expected proportional relationship between the input signal and the valve position should be achieved.<\/p>\n\n
Common Mistakes in 4\u201320 mA Calibration<\/strong><\/p>\n\nCertain mistakes made during calibration can cause the positioner to operate incorrectly.<\/p>\n\n
Incorrect Zero Adjustment<\/strong><\/p>\n\nIf the valve does not reach its actual starting position at 4 mA, the zero adjustment may not have been performed correctly.<\/p>\n\n
Incorrect Definition of Maximum Stroke<\/strong><\/p>\n\nIf the valve does not reach the fully open position at 20 mA, the maximum stroke setting should be checked.<\/p>\n\n
Incorrect Actuator Direction<\/strong><\/p>\n\nIf the positioner\u2019s opening and closing direction does not match the actuator\u2019s actual direction of movement, the response to the 4\u201320 mA signal may be reversed.<\/p>\n\n
In this case, the direction or operating mode settings on the positioner should be checked.<\/p>\n\n
Insufficient Air Pressure<\/strong><\/p>\n\nIf the air pressure is insufficient, the actuator may not be able to move the valve to the target position.<\/p>\n\n
In this case, instead of repeating the electronic calibration, the pneumatic system should be checked first.<\/p>\n\n
Mechanical Play and Friction<\/strong><\/p>\n\nEven if the positioner receives the correct signal, friction and mechanical play in the valve stem, packing, actuator, or linkage mechanism can cause positioning errors.<\/p>\n\n
In control valves, a sticking-friction problem known as stiction can also affect the stability of position control. <\/p>\n\n
How Is Valve Position Calculated from a 4\u201320 mA Signal?<\/strong><\/p>\n\nIn a standard 4\u201320 mA system, the following formula can be used to approximately calculate the valve position:<\/p>\n\n
Valve Position (%) = (Input Current \u2212 4) \/ 16 \u00d7 100<\/strong><\/p>\n\nFor example, if the input signal is 12 mA:<\/p>\n\n
(12 – 4) \/ 16 \u00d7 100 = %50<\/strong><\/p>\n\nAs a result, a 12 mA signal corresponds to approximately 50% valve position.<\/p>\n\n
Similarly:<\/p>\n\n
\n4 mA \u2192 %0<\/li>\n\n\n\n 6 mA \u2192 %12,5<\/li>\n\n\n\n 8 mA \u2192 %25<\/li>\n\n\n\n 10 mA \u2192 %37,5<\/li>\n\n\n\n 12 mA \u2192 %50<\/li>\n\n\n\n 14 mA \u2192 %62,5<\/li>\n\n\n\n 16 mA \u2192 %75<\/li>\n\n\n\n 18 mA \u2192 %87,5<\/li>\n\n\n\n 20 mA \u2192 %100<\/li>\n<\/ul>\n\nThis calculation is valid for a linear signal-to-position relationship. If the valve characteristic is linear, equal-percentage, or another characteristic, the actual change in flow may not occur at the same rate. <\/p>\n\n
What Should Be Checked After Calibration?<\/strong><\/p>\n\nAfter calibration is completed, it is recommended to test the system not only at the two end points but also at various intermediate positions.<\/p>\n\n
For example, 25%, 50%, and 75% command values can be applied to observe the valve movement.<\/p>\n\n
At the same time, it should be checked whether the command value displayed on the PLC or DCS screen is consistent with the actual valve position in the field.<\/p>\n\n
If significant deviations in valve position are observed despite the signal being correct in the control system, the issue may not be caused by calibration alone. The positioner settings, actuator, valve mechanism, air supply, and feedback mechanism should be evaluated together. <\/p>\n\n
<\/span>UNOX Electropneumatic Positioners<\/strong><\/span><\/h4>\n\nThe UNOX product range includes Rotary Electropneumatic Positioners and Linear Electropneumatic Positioners.<\/p>\n\n
Rotary positioners are used in rotary valve and actuator applications, while linear positioners are used in applications requiring linear movement. The product pages specify the positioners\u2019 applications in industrial automation and precision valve positioning. <\/p>\n\n
UNOX also offers pneumatic on-off and pneumatic proportional control valves in its product range. Therefore, evaluating the positioner, actuator, and control valve together is important for developing an automation solution suitable for the application. <\/p>\n\n
<\/span>Conclusion<\/strong><\/span><\/h5>\n\nIn electropneumatic positioners, 4\u201320 mA calibration<\/strong> is an important adjustment that ensures the electrical signal from the control system is correctly matched to the valve position.<\/p>\n\nIn general:<\/p>\n\n
4 mA \u2192 Minimum position<\/strong>12 mA \u2192 Approximately 50% position<\/strong>20 mA \u2192 Maximum position<\/strong><\/p>\n\ncan be established in this way.<\/p>\n\n
However, for proper calibration, adjusting only the 4 mA and 20 mA values is not sufficient. The pneumatic air pressure, actuator direction, valve mechanism, feedback linkage, and positioner settings should also be checked. <\/p>\n\n
Especially in applications involving precise process control, selecting the correct positioner and performing proper calibration are critical to ensuring stable system operation.<\/p>\n\n
For more information about UNOX electropneumatic positioners and actuated valve solutions, it is important to review the product technical specifications and determine the model best suited to the application.<\/p>\n\n