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[Keywords] Samson fieldbus valve positioner working principle joint connection operation troubleshooting 1 Introduction Zhonghai Petroleum Jianye Chemical Co., Ltd. annual output of 600,000 tons of methanol plant 100 units, 150 units, 300 units, 800 units, etc., a large number of Samson site Bus valve positioner, bus positioner in the control and operation is quite different from the previous 4-20mA positioner, so it is necessary to master the principle and use method.
2 Structure and operation of the Samson valve positioner The digital valve positioner receives the reference variable (reference variable w) transmitted via the fieldbus and compares it to the stroke or angle of rotation of the control valve (control variable x). The positioner sends a pneumatic signal pressure (output variable y) to match the valve position to the input.
The positioner consists of a displacement sensor system proportional to the resistance, an analog i/p converter with a downstream air volume enhancer, and electronic components including a microcontroller.
The position of the valve is transmitted to the analog PD regulator via a collection arm and a displacement sensor in a linear stroke motion or rotation angle. At the same time, the A/D converter transfers the position of the valve to the microcontroller. The PD adjuster compares this actual value with the FOUNDATION fieldbus reference variable that is cyclically transmitted by the control device.
If there is a system deviation, the operation of the i/p converter changes to the actuator being inflated or emptied by the latter air volume booster. This will cause the closing part of the regulating valve to which it belongs (such as the spool) to move to the position determined by the reference variable. Pneumatic air volume boosters and pressure regulators provide compressed air supply.
3 The engagement positioner with the control valve can be directly engaged with the SAMSON 3277 actuator or with a control valve with a cast iron frame or a cylindrical frame according to IEC 60534-6 (NUMAR) or with a rotary actuator according to VDINDE 3845 .
Depending on the type of positioner engagement, the signal pressure can be passed through the hole to the actuator head through the hole on the left or right side of the frame. Depending on the safe reset position of the actuator "Actuator stem extension" or "Actuator stem contraction" (if the air supply fault valve is open or closed), the switching plate must first engage the actuator frame. Press the marker (visible on the switchboard) to adjust the switchboard with the left or right side to engage the corresponding symbol.
The installation steps are as follows:
(1) Install a connecting plate or a pressure gauge frame with a pressure gauge on the positioner, and confirm that the positions of the two sealing rings are properly placed.
(2) Remove the vent plug on the back of the positioner and close the pressure output "Output38" on the connecting plate or gauge frame using the plug included in the accessory.
(3) Place the follower clip on the actuator stem, adjust and tighten the screw so that the mounting screw is in the groove of the actuator stem.
(4) Install a cover plate with a narrow opening with a slit opening point at the signal pressure interface. Verify that the gasket it is facing faces the actuator frame.
(5) Remove the follower pin on the arm M from the pin position 35 on the back side of the positioner, reposition it in the hole of the pin position 25 and tighten the screw.
(6) Pressing a formed seal ring into the groove of the retainer housing.
(7) Place the positioner on the cover so that the follower pin stops at the top of the follower clip. Adjust the arm accordingly and open the positioner cover to stop the positioner's shaft at the lid or rotary switch position. The arm must be parked at the follower clip with spring force.
Use two setscrews to install the positioner on the cover.
Make sure that the seal is inserted into the hole in the intermediate plate during installation.
(8) Install the cover on the other side. When the condensate can be collected and discharged after the regulator is installed, make sure the vent plug is down.
4 Operation 4.1 Operator Control and Display 4.1.1 Rotary Button The positioner is primarily operated using the rotary button. Select or set the code, parameters and values ​​by pressing the ◎ button and press it to confirm.
4.1.2 Sliding switch air opening or air closing This switch is used to adapt the positioner to the operating direction of the actuator. For the actuator of the supply pressure opening valve, the safety reset position: "spring closing valve": switch position AIRTO OPEN. For the actuator of the supply pressure shut-off valve, the safety reset position: "spring open valve": switch position AIR TO CLOSE. For positioners that engage an inverting amplifier for a two-acting rotary actuator: switch position AIRTO OPEN. The setting switch position should be set before initialization, and the setting after initialization is invalid.
4.1.3 Capacity Limiter Q
The capacity limiter is used to adapt the air supply to different size actuators. Depending on how the air is connected in the actuator, there are two fixed settings available: For actuators less than 240cm2 and side signal pressure connection (Type 3271-5), select MIN SIDE. The signal pressure is connected to the back (model 3277-5) and MIN BACK is selected. For larger actuators, select MAX SIDE for side connections and MAXBACK for back connections.
4.2 Enabling and selecting parameters Before the relevant parameters are configured, code 3 must be used to enable the state. To cancel the value just entered under a certain code, turn the button until the ESC appears on the display panel and press this button 0 to confirm. If the input is not set within 60 seconds, the enable configuration function becomes illegal and the display returns to code 0. After the positioner is engaged on the valve and the safety reset position and the capacity limiter are adjusted, it can be operated in a standard state, and the initialization button is activated to ensure optimal operation of the positioner.
5 Fault handling In the fault state, the fault symbol - appears in the upper left corner of the panel.
Err and the corresponding error code appear on the panel, first use Code 3 to set the enable configuration, and then to the error code to confirm.
Code 50, X> Range: The value provided by the measurement signal is either too high or too low to measure the sensor position near the mechanical limit. the reason:
(1) The pin position is incorrect;
(2) The frame or positioner sliding in the NAMUR engaged state is not centered;
(3) The follower plate is not properly engaged.
If the error is prior to initialization, move the valve to a safe reset position to prevent damage to mechanical parts. Correction: Check the joint and pin position and reinitialize the unit.
Code 51, Δx < range: The measurement range of the sensor is too small. the reason:
(1) The pin position is incorrect.
(2) The arm is incorrect.
Correction: Check the joint and reinitialize the unit.
Code 52, Engagement: Reason:
(1) The device is not properly engaged.
(2) The nominal stroke/angle is not reached in the initialization state of the NOM or Sub mode.
(3) Mechanical or pneumatic errors, such as selecting an incorrect arm or moving the supply pressure to the desired position is too low.
Correction: Check the engagement and supply pressure and reinitialize the unit. By entering the actual pin position and then initializing under MAX, the maximum stroke/rotation angle can be checked in some cases. After initialization is complete, Code 5 shows the maximum stroke or angle of rotation that the valve can reach.
In the event of an error in the closed position of the valve, such as with a soft-seal spool, the zero point must be re-calibrated.
During the test run, the positioner communication interruption (CNF) occurred and the valve was closed. This can be solved by upgrading the positioner version and replacing the positioner.
6 Conclusion A large number of SAMSON valves and positioners were used in the 600,000-ton methanol project. Among them, a communication interruption occurred during the PV010102 test, and the version of the positioner was upgraded. Individual valves such as LV010702 sometimes have an open output (OOP) and are automatically restored without affecting operation. For the new FCS system, the SAMSON locator is basically running normally, but there are certain risks. While learning the principles and operating methods of valves and positioners, we have summarized the experience of on-site maintenance and achieved good results.
The paper introduces the working principle of Samson fieldbus valve positioner, the connection with the regulating valve, the line connection, the operation method and the fault handling method.