Share optimized solutions, professional valve knowledge and industry news

Please enter the relevant terms or keywords you need to consult, and relevant articles will appear in the search results. If you can’t find the answer you need, please feel free to contact us and we will be happy to help. Or you can directly send an email to [email protected]

What is the controller in the control valve?

The controller gets a feedback signal from the processing, compare it with the variable parameter and the desired data, then decides to send a signal to operate the valve action.
Table of Contents
    Add a header to begin generating the table of contents

    The control valve is equipment or system that regulator the capacity of air, water, steam, or other liquid. The main function of the control valve is to modulate the gas or liquid, the valve can be open or close, or open at any travel position.

    We know that the common control valves can be divided into two kinds of pneumatic and electric control valves, for different actuation types, the controller is also different. Due to the control valve can’t open or close by itself, so we need a controller to send a signal to the valve actuator, valve positioner, or pilot to control the valve opening.

    1. Pneumatic control valves

    A pneumatic actuated control valves use a pneumatic pilot as a controller, and the valve mechanical positioner, or digital/smart positioner received the signal from the controller. 

    2. Electric control valves

    Electric actuated control valves use an eclectic pilot as a controller, it can be a programmable logic controller or remote terminal unit.

    How does a pressure valve controller work?

    It is important to point out that not all control systems need a controller. For example, an on-off valve and actuator can be operated directly from a thermostat. The operation of high limit safety controls can be used to close valves or switch off fuel supplies.

    So a controller is needed when the control applications requirements become more advanced and complex. The controller gets a feedback signal from the processing, compare it with the variable parameter and the desired data, then decides to send a signal to operate the valve action.

    controller sends signal
    controller sends signal

    Pneumatic controllers were popular controllers a decade ago, but now they use usually refers to situations in hazardous areas where the risk of an electrical or electronic explosion is ruled out in order to use a pneumatic controller, so not only is it safe to use a pneumatic controller, but it costs less than most of the popular electronic digital, or microprocessor controllers available today.

    The functions carried out by the controller can be very complex and it is beyond the scope of this publication to explain how they work. There are a number of major variations that need to be considered, we just list the major variations for your reference.

    1. Pressure valve controller for single-loop

    A single-loop controller is used to operate one valve/actuator from a single sensor.

    a single loop temperature controller
    a single loop temperature controller

    A single loop controller has the ability to perform ramp and dwell functions. It may have a typical multi-sequence pattern like the one shown as blow. In this figure a series of ramps (temperature change) and dwell functions (maintaining temperature) were carried out over a period of time.

    Typical multi-sequence ramp and dwell pattern

    typical multi sequence ramp and dwell pattern

    2. Control valve controller for multi-loop

    A multi-loop controller has the ability to operate more than one valve/actuator from more than one sensor.

    3. Single Signal

    The single signal means the controller only accepts one signal from the sensor and sends it to the actuator.

    4. Multi-Signal

    The multi-signal means the controller can receive multiple signals from the sensor and sends them to the actuator.

    5. Real-time

    Real-time may include a time clock to switch at pre-determined, pre-set times.

    6. Elapsed time

    Elapsed time means before or after other items of plant are switched on or off, it may switch at a pre-set time.

    7. Sensors and Transducers

    A wide variety of sensors and transmitters are required in control systems to monitor pressure, temperature, liquid level, or other physical characteristics. Sensors are a very important part of the control system, through which changes in the controlled variable are sensed.
    Small changes in resistance emitted by a sensor in response to a change in temperature may be converted to voltage or current for onward transmission to the controller. That is, the signal from the sensor may be so small that it can be adjusted and amplified locally by a change in temperature that causes a change in voltage, or possibly a change in resistance, for effective reading.
    Due to the resistance generated by the wiring and the effects of electrical interference, there will be some deviation in the transmission process.

    8. Liquid-filled and gas-filled system sensors or pressure system

    The filled system sensors are used with pneumatic controllers. The term ‘Programmable Logic Controller (PLC)’ is frequently used in control literature. In a process, the controller must initiate a sequence of actions, such as turning valves or pumps on or off. In some conditions, the whole sequence is on a timed basis but often the various steps may be triggered by a specific condition being reached and maintained for a certain time period. For example, A vessel is filled or a certain temperature is reached. The process can be controlled by a PLC that uses a standard interface for actuators and sensors.

    The mill room controller is another complex controller type,  generally, it may be used to control the pump, heating control valve, boiler, or other equipment. 

    The filling medium used mercury in the past years, but due to health and safety problems, now uses inert gas in the filled sensor system, such as nitrogen gas. When the temperature increases, the filled fluid expands and causes the Bourdon tube to uncoil; when the temperature decreases, the filled fluid contracts, and causes the Bourdon tube to coil more tightly. This coil motion is used to operate the levers within the pneumatic controller, allowing it to accomplish its task. The pressure-sensing version will typically use simply a pressure tube connected to the Bourdon tubing. 

    liquid filled and gas filled system sensors or pressure system
    liquid filled and gas filled system sensors or pressure system

    9. RTDs(Resistance temperature detectors)

    RTDs play a role like electrical transducers that convert temperature alters to changes in electrical resistance. As the temperature changes, the electrical resistance of certain metals changes too. The following figure shows the relationship between resistance and temperature for the Pt100 sensor. (Nickel, platinum, and copper are the metals that meet resistance temperature detectors requirements)

    resistance and temperature for the pt100 sensor
    resistance and temperature for the pt100 sensor

    The change in resistance from 0C to 100C is specified by the resistance temperature detector. Platinum RTDs are used the most for typical applications. Pt 100 sensors are constructed with a resistance of 100 ohms at 0°C, and with high accuracy between 0°~100°C when they can be used over a temperature range of -200°C to +800°C. According to the resistance and temperature chart, the resistance increases almost linearly with temperature, the Pt100 has a relatively small change in resistance, which needs to be carefully measured. The resistance in the connection cable needs to be properly compensated.

    10. Thermistors

    Thermistors use a semiconductor material whose resistance varies greatly with increasing temperature but is nonlinear. The resistance decreases with increasing temperature(NTC-negative coefficient thermistor).

    PTC Positive coefficient thermistors can be made if the resistance increases with rising temperature, but their response curve makes them unsuitable for temperature detection.

    Thermistors are less complex and less expensive than RTDs, but they do not have the same accuracy and repeatability. The resistance of the connecting cable is unimportant because of its high resistance.

    Thermistors do not have the same high accuracy and repeatability that RTDs do, but its less complex and less expensive. Their high resistance means that the resistance of the connecting cable is less important.

    negative coefficient thermistor

    11. Thermocouples

    We all know that any pair of different metals can be used to make thermocouples, but the common standard types are J-type, K-type, T-type, and others. Of these, the most widely used general purpose thermocouple is type K.

    The dissimilar metals used in type K thermocouples are chromium (90% nickel, 10% chromium) and aluminum (94% nickel, 3% manganese, 2% aluminum and 1% silicon) and can be used in the range of 0°C to 1260°C. For the material of the extension tails, it is possible to make the same material as the thermocouple itself wire, also
    It may also be a compensation cable made of copper and copper-nickel alloy. It is important to note that both extension wires must be of the same material.

    There are a wide variety of sizes and shapes of thermocouples. Over a wide temperature range, they are affordable, rugged, and quite accurate. However, the reference junction temperature must be kept at a constant value, otherwise, the deviation has to compensate for. Low junction voltages mean that special shielded cables and careful installation must be used to prevent electrical interference or “noise” from distorting the signal.

    12. Digital addressing

    Digital addressing allows the controller to send messages over a set of wires that have several receivers attached to them but are only able to communicate with one of them if needed. This is accomplished by assigning an address to each receiver, which the controller must first broadcast.

    There are there common digital addressing in the control system, HART, PROFIBUS Fieldbus(PF), and Foundation™ Fieldbus(FF).

    What is HART communication protocol? 

    HART communication protocol, which stands for Highway Addressable Remote Transducer, is a standard originally developed as a communication protocol for controlling field devices that operate on a 4-20 mA control signal. HART® is an industry standard for defining communication protocols between control systems and intelligent field devices. The most widely used digital communication protocol in the process industries is HART®. Here are some reasons:

    • All of the major suppliers of process field instruments are supported by HART® communication protocol.
    • 4-20 mA signals are allowed to co-exist with digital communication on existing 2-wire loops to preserve existing control strategies.
    • It is compatible with analog devices.
    • HART® communication protocol supplies some valuable information for installation and maintenance, such as product information, range and span data, measured values, Tag-IDs, and diagnostics.
    • The use of multidrop networks can support the savings of the cabling.
    • Improved management and use of smart instrument networks reduce operating costs.

    What is PROFIBUS Fieldbus(PF) communication protocol? 

    Because PROFIBUS® is an open Fieldbus standard, it is manufacturer-independent and therefore has a wide range of applications in manufacturing and process automation. Any special interface adjustment can be required to communicate between devices of different manufacturers.

    PROFIBUS® is suitable both for high-speed, time-critical applications and for complex communication tasks. It supplies functionally graded communication protocols DP and FMS. depending on the application, transmission technologies can be used such as RS-485, IEC 1158-2, or fiber optics.

    PROFIBUS® defines the technical characteristics of a serial Fieldbus® system with which distributed digital programmable controllers can be networked from the field level to the unit level. PROFIBUS® is a multi-master system and thus allows several automation, engineering, or visualization systems to operate jointly with their peripheral devices distributed on a single bus.

    What is Foundation™ Fieldbus(FF) communication protocol? 

    The Foundation™ Fieldbus communication protocol is an entirely digital, serial, bi-directional communication system that serves as a local area network (LAN) for plant instrumentation and control facilities. The Fieldbus® environment is the foundation-level digital network group in the plant network hierarchy. Foundation™ Fieldbus is used for both process and manufacturing automation applications and has the built-in capability to distribute control applications over the network.

    13. Interoperability

    Foundation™ Fieldbus provides interoperability, a Fieldbus® device can be interchanged by similar devices with additional features from different vendors on the same Fieldbus® network, while keeping the specified operation. This allows users to “mix and match” field devices and host systems from different suppliers. Individual Fieldbus® devices can also communicate and receive multivariate data and transmit them directly to each other via a common Fieldbus®, allowing new devices to be added to the Fieldbus® without interruption of service.

    Facebook
    Twitter
    LinkedIn
    Pinterest
    Print
    Picture of Will Don

    Will Don

    After earning my bachelor's degree in mechanical engineering from Zhejiang Normal University in 2008, l was fortunate enough to begin my career with Siemens, Fisher, and YTC, focusing on control valve accessories. Over the past dozen years, l've poured my heart and energy into understanding technology and fluid solutions for control valves.
    Now, as the marketing director for THINKTANK, a trusted branch of the Taiwan STONE valve group, I can't help butf eel proud of how far we've come. Our knowledge isn't just reaching professionals like engineer and valve distributors; it's also inspiring the next generation of automation college students.
    l genuinely hope you're enjoying our articles and finding them helpful.Your thoughts, questions, and feedback mean the world to me, so please don't hesitate to reach out to marketing[at]cncontrolvalve.com. Whether you're a seasoned expert or just curious about the field, I'm here to connect, share, and learn together.

    All Posts »

    I am the author of this article, and also the CEO and marketing director of THINKTANK, with 15 years of experience in the industrial valve industry. If you have any questions, you can contact me at any time.

    Subscribe Now

    Receive the latest product information and industry news.

    We value your privacy. Your information will be kept confidential.

    Contact Us

    Just fill out your name, email address, and a brief description of your inquiry in this form. We will contact you within 24 hours.

    The Latest News
    axial piston high pressure pump

    High Pressure Pumps Axial Piston Pumps

    In the past 5 years, we made our HPR/HPH series axial piston pumps as OEM products for a well-known brand. These pumps have been successful ...
    Read More
    breaker valve manufacturer

    VB14 and VB21 Vacuum Breaker Installation

    VB14 Vacuum Breaker Description VB14 is a small special vacuum breakers used in condensing vapour/steam or liquid systems, and it made of Brass material, and ...
    Read More
    common valve abbreviation guide

    Common Valve Abbreviation Guide

    In industrial manufacturing and instrument maintenance, you’ll see many abbreviations for valves. It’s important for engineers, maintenance people, and students to know these abbreviations because ...
    Read More
    spray & fuse coating

    Comprehensive Technical Guide on Hard Coating For Severe Service Valve

    One of the most effective ways to improve the durability and performance of valves in in severe service environments, where valves are work at extreme ...
    Read More
    dosing valve DN100 lime dosing system

    What is a Lime Dosing Valve and How Does It Work

    In the world of water treatment and chemical processing, it’s important to control lime dosing accurately. Getting the pH right and avoiding lime blockages can ...
    Read More
    concentrated solar power schematic

    Selection and Application of Molten Salt Control Valves

    In recent years, as the environmental impact of traditional energy sources such as coal and petrochemicals has become more and more of a concern, there ...
    Read More
    molten salt power system

    Comprehensive Guide of Molten Salt Valve

    In the world of advanced energy systems, molten salt valves are a critical component for controlling high-temperature fluids that are important for storing and transferring ...
    Read More
    lined ball valves akh5

    Top 10 Ceramic Valves Manufacturers in 2024

    Ceramic valves are used in highly demanding services including slurry, erosive, corrosive, and scaling applications.
    Read More
    globe control valve body

    Información sobre los tipos de válvulas industriales

    Existen numerosos tipos de válvulas industriales, que pueden alcanzar hasta varios cientos, y cada tipo de válvula está diseñado para satisfacer las necesidades específicas ...
    Read More

    Contact Us

    With expertise in valves and rich experience in the oil&gas, chemical industry, textile mills, power plants, and sugar mills. THINKTANK has become the premier manufacturer of next-generation precision control valves.

    With a customer base that includes over 42 of the world’s leading engineering&contractors and international valve brands, THINKTANK Valves offers cost-effective valves that help our customers achieve automated process control without paying high prices.

    Why are more and more international valve brands choosing THINKTANK for OEM service?

    Brand is reputation, which not only requires high valve technology, but also great comercial support and fast response after-sales service and delivery time. They will not gamble their brand on an unknown product

    Get an Instant Quote

    Avoid your inquiry is delay response, please enter your WhatsApp/Wechat/Skype along with the message, so we can contact you at the very first time.

    We will reply you within 24 hours. If for urgent case, please add WhatsApp: +86 185 1656 9221, or WeChat: +86 199 2125 0077. Or call +86 189 5813 8289 directly. 

    Get An Instant Quote

    Joy Preview

    Get An Instant Quote

    We will reply you within 24 hours. If for urgent case, please add WhatsApp: +86 199 2125 0077, or WeChat: +86 199 2125 0077. Or call +86 189 5813 8289 directly. 

    Direct to Control Valve Factory With Competitive Price & Reliable Quality

    Joy Preview
    Joy Preview

    Get An Instant Quote

    Just leave your name, email, and simple message or requirements, We will contact you within 1 hour.

    WhatsApp: +86 199 2125 0077

    Skype ID: sowell85

    Wechat ID: +86 199 2125 0077