Electro-Pneumatic Positioner-FAQ

The electro-pneumatic positioner works on the force balance position to place the valve stem after receiving the signal from the controller. These valves use compressed air and signals to obtain data from the controller. Depending on the sign, the input expands or compresses.

This guide will discuss the electro-pneumatic positioner’s functioning and specifications to understand the instrument better.

1. What is an electro-pneumatic positioner?

The electro-pneumatic positioner has three main parts, body, actuator, and positioner. The purpose of the pneumatic positioner is to convert the signal from the control system for sending pressure to the actuator. The positioner tells the actuator to move the valve to a specific position based on the input.

The electro-pneumatic positioner is the tool that converts a 4-20mA input into the pneumatic output by positioning the control valves. The air actuator in the electro-pneumatic positioner controls the valve position and flow. This equipment provides reliable services in various rugged applications.

2. How does the electro-pneumatic positioner works?

The electro-pneumatic positioner is a force balance device that maintains the position of the plug. This is done by comparing the forces from the control valve stem and control signal using the motion connector.

It uses a flapper or nozzle system that needs compressed air to work effectively. The electro-pneumatic positioner uses a signal of 3-15 pounds per square inch for receiving data.

The input results below to expand or compress. The bellows move the flapper and the beam that measures the valve stem. The movement of the flapper results in getting closer or away from the nozzle, which increases or decreases the air output to the actuator. The movement of the valve stem sends feedback via the beam. The air output will again increase or drop for positioning the valve based on the input signal.

3. What is the working principle of an electro-pneumatic positioner?

The working principle of the electro-pneumatic positioner is similar to the pneumatic control valve. The only difference is that it uses analog signals, using 4-20 milliamps. The instrument air signal plays an essential part in driving the diaphragm. The electromotive force (EMF) is used to change the air to the valve actuator. It has two main components, a pneumatic positioner and a manifold coupled I/P converter.

The pressure of 145 PSI connects with the supply port of the unit, and the actuator ports connect with the single or double-acting actuator. The opening port of the electro-pneumatic positioner is a C+ port. An instrument signal of 4-20mA is associated with the IP connection block, which should be plugged.

When there is no electronic signal in the unit of the electro-pneumatic positioner, the positioner remains stable with no actuator movement. The Pneumatic positioner is coupled with the I/P, which can be mounted internally or externally with the help of an adaptor.

Air supply for I/P convertor is up to 145 psi that through the positioners supply port. I/P converter will convert the 0-10V DC signal into a 3-15 psi signal to the positioner diaphragm. I/P convertor responds when there are voltage changes. It sends the pneumatic signal internally to the diaphragm, causing the diaphragm and spool valve to move and send air to the actuator.

The movement of the actuator causes the spindle/cams movement and turns to the desired set point based on the mA input signal. Once you achieve the set point, you can balance the supply air between ports.

4. What are the benefits of an electro-pneumatic positioner?

The electro-pneumatic positioner is used in control valves in the valve are pneumatically operated using electrical controller or control systems. The valve uses the control signal of 4-20mA and converts this signal into the pneumatic output. Following are the benefits of electro-pneumatic positioner:

• The electro-pneumatic positioner is applicable for split range applications.
• It has an easy feedback connection and is easy to convert from ATO (Air to Open) to ATC (Air to close) or vice versa.
• It provides fast and accurate responses and uses low air consumption.
• There is no change in performance in the range of 5-200Hz of vibrations.
• The electro-pneumatic positioner has precise digital control and is designed with ease of installation, cost-effectiveness, efficiency, and simple calibration.

5. What are the features of an electro-pneumatic positioner?

• When operating the electro-pneumatic positioner, the unit optimizes control behavior in response to the changes inline media pressure.
• It has corrective and preventive maintenance features with self-diagnostic checks. The diagnostics constantly run throughout the operation and are also monitored and recorded.
• The electro-pneumatic positioner also has an internal monitoring feature that provides the signal alarm for air supply failure. The warning is shown on the LCD and sent to the remote control panel.
• The valve position in the electro-pneumatic positioner can be adjusted manually by removing the housing cover. After that, the pushbuttons are used to override the remote control signal.
• There is precise control of most miniature pneumatic actuators by using internal flow restrictors.
• There is a position indicator in addition to LCD that shows the valve position from a distance.

6. What are the specifications of an electro-pneumatic positioner?

The electro-pneumatic positioner is a dustproof and waterproof body. It has a centralized exhaust system that has the combination of labyrinth effect and check valve that enhances the waterproof performance of the equipment. The electro-pneumatic positioner has the transmission analog output of 4-20mA DC and the alarm output function of two points. It has the material of aluminum and can act as a single or double-acting actuator.

The lever and rotary type of electro-pneumatic positioner have an easy adjustment transmitting type. The construction of the positioner is explosion-proof. The built-in sensor of the electro-pneumatic positioner allows easy remote change and monitoring. For the easy setting of various parameters, there is the option of an internal push button. As compared to the other positioner in the market, it has zero points and span adjustment.

7. What are the parameters of an electro-pneumatic positioner?

• The reverse operation setting of the electro-pneumatic positioner responds to the operation direction about the input signal.
• The split range setting changes the range of the input signal.
• You can change the actuator range concerning the input signal through the span adjustment setting of the positioner.
• There is a parameter of forced complete close/whole open setting in the electro-pneumatic positioner. The force actuator opens to 0% and 100% for closing the valve in response to the input signal.
• There are four-valve characteristics: linear characteristics, equality characteristics of two types, quick open feature of two kinds, and user-preferred point setting of 11 points.
• You can make actuators’ upper and lower stroke limits with the output setting of alarms 1 and 2.
• You can increase or decrease the analog output setting 4 to 20 mA DC in response to actuator stroke.

8. What is the design of the electro-pneumatic positioner?

The electro-pneumatic positioner controls the valve position and has a simple design and structure. Two essential components of an electro-pneumatic positioner are a pneumatic positioner and an I/P converter.

The control unit receives the control signal compared to the rotational angle of the control valve and issues pressure. There is a coupling wheel that transfers the rotary motion for rotary actuators. These rotary actuators need reversing amplifiers to permit the operation.

The positioner has a sensor system that responds based on resistance and an analog module with a microcontroller. The positioner has three binary contacts as standard. In addition, the fault alarm output has been installed to identify any fault to the control station, and two configurable software switches indicate the valves’ positions.

The position of the valves is transmitted as rotation via travel sensor and pick-up lever, PD controller, and A/D convertor. The PD controller compares 4 to 20mA DC signal once it is converted into an A/D convertor.

When there is an issue in the system, the i/p converter changes and fills the actuator via downstream air capacity. The air capacity boosters in the electro-pneumatic positioner are provided with the supply air. In addition, there is an intermediate flow regulator that ensures the trouble-free operation of the promoter.

The electro-pneumatic positioner has an interface that allows transmitting data and parameters over an adaptor cable.

9. What are the advantages of an electro-pneumatic positioner?

The standard method of motion control in automation systems is electromechanical positioning. However, the electro-pneumatic positioner is gaining popularity, a more precise tool to control flow or pressure. Electro-pneumatic positioner offers many advantages, such as great productivity, reliability, and lower cost.

These instruments are more energy efficient as they only consume electricity to hold a position. When operating the electro-pneumatic positioner, the valve in the center blocks the airflow, due to which the piston stays intact. If the power is lost during the production process, you can easily restart production.

Also, the electro-pneumatic positioner is easy to repair. In case of any wear out or damage, it can be fixed easily. It also offers low maintenance and lower cost of ownership. The control valves, cylinders, and sensors depend on the flow control to control positioning.

10. What are the disadvantages of an electro-pneumatic positioner?

There are certain drawbacks of using an electro-pneumatic positioner. These systems cannot be adequately sealed; you can also avoid the loss of air or pressure. When operating the electro-pneumatic positioner, minor leaks cause the piston to move. The sensor sends the motion feedback to the controller. As a result, the controller adjusts flow to compensate for the movement of the piston. This motion affects the accuracy of the system and its functionality.

Although the cost of an electro-pneumatic positioner is relatively low, the operating and maintenance cost can be higher. Over the long run, the failure of electromechanical components can lead to increased production costs.

11. How to calibrate electro-pneumatic positioner?

The accuracy of the electro-pneumatic positioner depends on how accurately the equipment is calibrated. Electro positioners have fewer moving parts than analog positioners so that they can self-calibrate. Your control valve may not be working correctly if you have an analog positioner. The electro-pneumatic positioner monitors many variables in the valve, including air consumption, temperature, friction, and many more.

You can electronically calibrate and configure the positioner using local push buttons. Before delivery and operation of the electro-pneumatic positioner, they are tested and inspected for 0-100% of the range. For zero calibration, 0% of the input signal is given to the positioner to stabilize the valve’s position.

Adjust the zero position and supply loop of the input signal starting from 0% and 100%. It is returned for 0% to make sure that the zero was correctly calibrated. The span of the calibration should maintain the signal of input 0%. Repeat the procedure and supply the input signal for the perfect and more efficient electro-pneumatic positioner’s performance.

12. How to install the electro-pneumatic positioner?

The installation of the electro-pneumatic positioner must be done by qualified personnel with adequate knowledge and expertise, and for getting additional assistance, contact sales representative. For installing the positioner in industrial environments, you need to be extra cautious. The industrial environment is susceptible to various liquid and gaseous contaminants. If you expose the equipment to these contaminants, it can result in malfunctioning and inaccurate measurements.

According to the local codes of practice, you should install the EDGE I/P converter in the electro-pneumatic positioner. While installing the positioner in a hazardous environment, the dangerous installation codes must be followed. The contractor should install the electro-pneumatic positioner. The assemble mounting kit is used if the end-user acquires it.

13. How to overcome troubleshooting of electro-pneumatic positioner?

Issues arise while operating the electro-pneumatic positioner, and the instrument does not respond to the input signals. The supply of insufficient air and damaged diaphragm should be resolved by verifying the input pressure and substituting the group diaphragm. In addition, when there is an issue with installing piping between the positioner and actuator, you need to verify the connection between the two and correct the position.

The imprecise and inaccurate positioning is caused due to many reasons. Therefore, you need to identify the root cause effectively so that you can resolve the issue accordingly. The major causes of the inaccurate positioning are dirt gathering in the valve, leaked or damaged diaphragm, incorrect movement of CAM, and the wrong actuator dimension.

It would help if you replaced the diaphragm in case of a damaged diaphragm. In addition, the incorrect dimension of the actuator should be corrected by increasing the air supply pressure to a maximum of 150 psi. Another common issue with the operation of an electro-pneumatic positioner is reaching the position very slowly. To resolve this, clean the valve spool and change the filter regulator by changing the piping of the air.

13. How to maintain of electro-pneumatic positioner?

For maintaining the electro-pneumatic positioner, the assembling and dismounting procedures should be followed properly. If the diaphragm is not functioning correctly, you need to substitute the group diaphragm. For removing the group diaphragm, turn off the feeding air, and remove the screws that connect the diaphragm. Then carefully remove it and put back the diaphragm. You should follow these steps to put back the group diaphragm carefully.

If you want to prevent any damage to the electro-pneumatic positioner, first verify the surface of the group diaphragm before installing it. Next, remove any dirt, contaminations, and dust from it. Finally, make sure that the sealed ring is not damaged or in bad condition.

Put the diaphragm in the base by aligning it correctly with the holes. Then, with the help of screws, tighten the group diaphragm in the ground and verify the operation.

14. How to substitute group spool in electro-pneumatic positioner?

For removing and substituting the group spool, first, turn off the feeding air. Next, remove the screws from the spool and remove the group spool. Putting back the spool kit is a tricky task, and you need to follow the steps correctly.

First, verify the surface area of the spool and the site before removing and installing the group spool. The surface should be free from dirt and contaminations. Next, remove the group spool and put it in the base. Make sure that it is appropriately aligned with the holes. After placing the group spool in the base, use two screws to tighten it and verify the operation.

15. How do type and rotary type lever works in electro-pneumatic positioner?

The electrical current inside the electro-pneumatic positioner changes according to the increasing input current. Therefore, the motor coil will also change through the input, output, and operation processes. This causes nozzle back pressure to decrease and nozzle to fall.

The pilot valve moves in the right direction, which increases the output pressure of Output 1 and reduces the Output 2 pressure. When the actuator moves, it causes the feedback spring, shaft, CAM, and lever to get balanced due to the input current.

When measuring the principle of operation of lever type in the electro-pneumatic positioner, the increase in the input will change the input process through the plate. It will also change the operation process and the output. Due to this, the armature will oscillate, increasing the clearance between nozzle and flapper—the pilot valve shifts to the right, and output pressure increases. The diaphragm valve moves, and the output position will match the input match.

16. What is the function of the YT-1200R series electro-pneumatic positioner?

This electro-pneumatic positioner has a double-acting actuator that opens and closes the valve. The single-acting actuator will close or open the valve automatically when power is lost. The limit switch box of the electro-pneumatic positioner gave the signal of valve opening and closing status.

After the calculation process and the valve position signal is set, the exhaust valve reaches the set point. In the process of loss of power, you can use manual operation. It has aluminum housing with an easy mounting stainless steel shaft and bracket. Therefore, you can operate the electro-pneumatic positioner in an extreme environment, short response time and economical air consumption.

17. What are the technical features of an electro-pneumatic positioner?

• The electro-pneumatic positioner gave the output signal pressure after comparing the input signal from the control system.
• It has four initialization modes for adjusting the control valve.
• It has a menu-driven operation with a simple single knob. Moreover, the LCD makes it easy to read any mounted position due to the reading direction.
• The present parameters make the adjustments of any valve deviating from the standard.
• It has a calibrated sensor without gears susceptible to wear. In addition, the substitution model of the electro-pneumatic positioner allows the positioner to start in case of an emergency.
• It has a two-wire system with a small electrical load between 300 and 350Ω. It also has the feature of continuous monitoring of zero points.
• The electro-pneumatic positioner has a temperature sensor to keep an eye on the temperature fluctuations.

18. What are the product precautions of electro-pneumatic positioner?

When you are operating the electro-pneumatic positioner, there are certain precautions that you should keep in mind. Do not operate the positioner outside the specific range of the equipment. The electro-pneumatic positioner should be designed to include the safety circuit, which prevents the risk of danger due to any positioner failure.

The exterior lead-in wiring is designed based on the guidelines for explosion protection, making it flameproof and explosion-proof construction. When the power is on, avoid removing the terminal cover. Instead, the terminal body should be appropriately placed while operating.

When the power is on, do not touch the actuator and oscillator as this could be dangerous. Before operating, cut off the pressure supply and release the compressed air inside the positioner. Always use the ground connection to prevent noise and damage due to static electricity.

Conclusion

The electro-pneumatic positioner provides a wide range of flow variations and uses piston actuators with air supply pressures. As a result, these pneumatic positioners are more economical and efficient.

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