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There are many different types of Fisher controllers, and today I would like to share with you some basic information about Fisher valve controllers. Principle of operation of the Fisher controller: 1. When the medium being controlled is high-pressure, high-temperature, low-temperature, flammable, explosive, or toxic, the packing is often compressed tightly to prevent leaks. However, this results in greater friction between the valve stem and the packing; this issue can be overcome using a Fisher positioner to eliminate delays. Similarly, when the medium being handled is a viscous fluid or contains solid suspensions, a positioner can be used to overcome the resistance exerted by the medium on the movement of the valve stem. 2. When the distance between the regulator and the actuator is over 60 m, a positioner can overcome the delay in the transmission of control signals, thereby improving the response speed of the valve. 3. When a regulator controls two actuators for step control, two positioners can be used to achieve step regulation, each receiving a high input signal or a low input signal; as a result, one actuator moves to a higher position while the other moves to a lower position. 4. The Fisher positioner is used in important control systems where high requirements are placed on control quality, in order to improve the positioning and reliability of control valves. 5. Used for large-diameter control valves with Dg>100 mm to increase the output thrust of the actuator. It is also suitable for applications with a large pressure difference across the valve (△p>1MPa). To overcome the unbalanced force exerted by the liquid on the valve core, increase the output force of the actuator by raising the air supply pressure, and reduce stroke error. Classification of Fisher valve controllers: Pneumatically operated valves receive an input signal from the process controller through a positioner, which is then used to determine the valve’s stroke. It can generally be divided into three types: 1. Analog I/P using a current signal of 4-20mA ； 2. Digital. The difference from the analog version lies in the conversion of signals ； 3. Pneumatic type, using air as the signal carrier. Positioning of Fisher valve controllers: A high gain is the most important characteristic of a good positioner when it comes to reducing process deviations. The gain of a positioner is mainly divided into two parts: 1. Dynamic gain: It refers to the ability to enable the actuator to respond quickly by providing the necessary drive force, after the change in the process variable is detected by the preamplifier, thus allowing the throttling element to act swiftly. Usually, to obtain sufficient power, a high dynamic gain power amplifier is needed for compensation. 2. Static gain: The high static gain of the positioner is achieved through the preamplifier. Sensitivity to detect minor changes in the input signal (such as <0.125%). Applications of Fisher valve controllers: When optimizing processes, Fisher controllers give priority to positioners for important valve applications. When used together with conventional digital control systems, positioners can provide high positioning accuracy as well as a faster response to process disturbances. Positioners can also be used in most specified control valve applications. The Fisher DVC6000 series are digital valve controllers. The DVC6030 model can be installed on any 90-degree rotating actuator, the DVC6020 model is suitable for use with rotating actuators as well as linear actuators with reciprocating motion, while the DVC6010 series is designed for use with linear actuators. Precautions for installing Fisher controllers: 1. Completely release the pre-tension of the actuator spring, and discharge the pressure in the pneumatic actuator. 2. Release the process pressure on both sides of the Fisher controller valve by using a bypass valve or by completely shutting down the process, thereby isolating the valve from the process pressure. 3. Ensure that the actuator does not suddenly open or close the valve. Disconnect all connection lines that supply air pressure, power, or control signals to the instrument. It is essential to note that a locking step should be employed to ensure that the above measures remain effective during the operation of the Fisher controller