Mitsubishi Heavy Industries Technical Review Vol. 58 No. 3 (September 2021)
1Servo Valve Automatic Adjustment(Automatic Adjustment System for High-Pressure
Electric Hydraulic Control Valve)
Control S ystems Department
Project Management Division
Mitsubishi Pow er Ltd.

Control valves using high-pressure electric hydraulic (EH) oil and a servo valve are used asfuel control valves for gas turbines, as well as for steam control valves for steam turbines in power
plants. Due to the recent adoption of the linear variable differential transmitter (LVDT), which isan accurate and durable position sensor, for the servo valve, these control valves have acomplicated mechanism and many adjustment items unlike pneumatic control valves, etc., sohigh-level skills are required for their various settings and sensitivity adjustments. The productpresented in this report uses learning circuits, etc., to program such expertise and techniques andhas made it possible to automatically and quickly achieve results equal to or better than those ofadjustment by engineers with high-level skills.

|1. Adjustment of Electric Hydraulic Control Valve
The adjustment of the servo valve is made by changing various settings on the control
device. Specifically, this adjustment includes the adjustment of the LVDT voltage value at the fully
closed and fully open position of the control valve, OFFSET adjustment that adjusts therelationship between the command value and the actual opening (feedback) value and GAIN
adjustment that adjusts the operating speed and operating behavior of the valve. These settings are
not irrelevant and need to be balanced as a whole and optimally adjusted.
Especially in terms of GAIN adjustment, in order to adjust the GAIN value to an optimum
value with which the control valve operates smoothly to the target value, it is necessary to checkand set the dynamic characteristics (behavior) of the control valve with an oscilloscope, etc., soexpertise and techniques, including judgment ability, are required.

|2. Features of servo valve automatic adjustment
Electric Hydraulic Control Valve automatic adjustment is a system that automatically adjusts
various setting adjustments such as LVDT voltage value adjustment, OFFSET adjustment, GAINadjustment, etc., which were previously made manually by engineers based on their expertise. Justby pushing a single button on the dedicated controller, the control valve automatically opens andcloses to sense its state and behavior, automatically making adjustments. In addition, GAINadjustment, which was previously made with an oscilloscope, etc., is performed automatically bymemorizing the behavior of the control valve at each GAIN value so that an optimum value isobtained. This system was realized based on DIASYS Netmation®, a control device that weproduce.
With this system, the working time for adjustment can be reduced, adjustments can be maderegardless of who is making them and the adjustment accuracy can be improved. Automatic
adjustment completes adjustments that previously required expertise and as much as one hour ofwork by an engineer in about 20 minutes. Since adjustment is made automatically, this systemenables the simultaneous adjustment of multiple control valves, which can lead to a significant
reduction in adjustment time. After automatic adjustment, all that is required is confirmation of
static characteristics (data collection in step increments of 25%, etc.) in a manner similar topneumatic control valves, so there is no need for expertise and this work can be carried out
regardless of the worker. In addition, because there is no variation caused by the feeling of theMitsubishi Heavy Industries Technical Review Vol. 58 No. 3 (September 2021)
2

engineer since adjustment is made automatically, the finishing accuracy is also improved. Figure 1
shows an accuracy scatter diagram of the adjustment results made by 6 engineers and the 6-time
adjustment results made by automatic adjustment, for 5 types of control valves. This indicates thevariation was reduced in the case of automatic adjustment.

Figure 1

Scatter diagram|3. Output function of dynamic characteristic test record
As a result of automatic adjustment, the record of behavior in the dynamic characteristics test
sampled every 50 msec is automatically output and can be easily graphed using a dedicated tool.
The operating time of the control valve and the excess amount (overshoot amount) of the control
value (actual opening) with respect to the control target value (command) are also automaticallycalculated.
Figure 2 below is a sample graph output.

Figure 2

Graph of dynamic characteristic test results|4. Future development
The application of this system is being promoted mainly in newly constructed plants. We
have also been working on the expansion of future application destinations and functions of thissystem, including at plants that have already been delivered and are in operation.