Several issues regarding switch-type electric actuators
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I just started working, and other things are fine, but I’m particularly struggling with the calibration methods for electric actuators. 1 I read the manual and now I understand the principles of on-off type actuators and proportional control type actuators, as well as the internal wiring and the principles related to the controller and servo amplifier. What’s unclear is whether, at the zero point and at the full travel position (with the potentiometer), adjustments are made manually using a handle, or whether signals are sent from a computer to make such adjustments. The approach I understand is to keep it turned down to 0 on the operator, and then adjust the potentiometer on-site. Can this be done manually? 2 There is a situation where the valve stem (output shaft) is already aligned with the zero indexing point, but it does not touch the lower limit switch; the mechanical zero point and the digital zero point do not match. Which one should be taken as the reference? The valve stem and the lower limit switch meet the requirements, but the ammeter gets connected to the feedback circuit on several occasions; in such cases the current is not even 20 mA, and it’s actually quite far below that value. I know the current should be slightly higher than 20 mA, but the difference is way too large
First, on-site adjustment is sufficient; after the adjustment is made, have the process engineers send a signal remotely so that they can confirm it. Second, is the zero scale you mentioned the actual mechanical zero? If so, adjust the limit so that it matches the scale; if not, adjust the scale accordingly, or using 4mA as the mechanical zero will work. Electric ones, just like pneumatic ones, require repeated zeroing and range setting. Another consideration is the function of the valve – whether it needs to be closed fully or opened fully. When the signal does not cover the full range, the process requirements take precedence.
Regarding the second issue, you need to adjust the lower limit limit switch; it might be loose, and you should use the mechanical zero point as a reference.
For the first question, an electric drive is necessary; adjust the potentiometer – one for the zero point and one for the range. When 4 mA is applied, adjust the zero-point potentiometer so that the valve is completely closed, and when 20 mA is applied, adjust the range potentiometer so that the valve is fully open. We used to adjust this frequently; feel free to ask if you have any questions
We have several digital actuators of the DDZ type here; they can be switched directly on the operator, and an analog dial pointer is used to indicate the degree of opening. They are not capable of outputting a signal of 4 to 20 milliamps. The technicians suspect that the feedback is inaccurate. Is it still possible to adjust them electrically in such a situation? Is it necessary to manually adjust the handwheel on-site? ? ?