Inductive analog sensors can be advantageous in the design of control systems of the machine. These sensors are particularly useful for applications requiring precision measurement and position detection, and for use in component coding. The final selection of a specific sensor, it is important to examine performance characteristics to the unit you choose is optimized to best suit the requirements of machine protection.

Inductive Machine Control
The sensors main reason why the industrial position with analog outputs are useful for system designers because of their ability to deny the need for discrete output switch. Instead of spending a quiet exit when an object reaches a certain distance from the face of the sensor, an analog sensor provides a variable output voltage and an output current proportional to the distance from the target sensor face.
Simplifying Machine Control Sensors Analog Design “Table 1 analog output signal of the sensor changes with the distance Source: Eaton ..”

This achievement is an ideal of analogue inductive sensor for applications that require precise position sensing and measurement. This type of functionality is very useful for an engineer end user the angular position of a rotating shaft to measure, for example. In designing an eccentric cam on the shaft and use the analog detector output proportional to the distance on the ridge, the designer can calculate the position of the axis.

In another application, such as inductive sensors analog deflection supervision of an essential element. For example, these sensors measure the axial deformation of a rotating blade, the control system can be designed to reduce speed on the sensor output, which makes them significant damage to the machine of a deformed sheet.
analogue sensors can also be used for component verification error, the identification of a cylinder to divert much of rejecting, for example. In another application of quality control typical insertion depth of a specific set of fixation or a secondary part of a measure and a series of control measures are taken based on the results. In more advanced systems, the sensors can be used for statistical process control to provide information (eg changes in section thickness measured in time).

Because many large inductive analog sensors to sensor manufacturers in this category and they all look at how the performance characteristics of a specific issue of analog sensors do? Where are all the same inductive analog sensors?

Questions Linearity
To answer this question, it is important to understand what is meant by the term “linearity” as applied to the outputs of analog sensors. This is illustrated by the solid line in Table 1.

In other words, an analog sensor that is “linear” has the same extent by the division during the full scale of the device. That means 1 mm change in the position of the object results in the same change in output voltage and current, or when the target object is in the range of the sensor envelope. In this case, the solid line represents the output of an analog sensor “linear”.
Simplifying Machine Control Sensors Analog Design “Table 2 non-linear signal output analog remote sensor Source: Eaton ..”

The dotted line represents a sensor with a nonlinear response. Using a device with the output characteristic, January 1 mm change in range of the target when this target in the middle of the range of the sensor will result in a change in voltage or current output is very different from the magnitude of change observed with the target on one side of the gamma-band or another.

How will this impact linearity characteristic of the design of your control? Consider an application where a cutting tool is located on a metal part in rotation, the position of the cutting tool according to the measured thickness of the material. If the thickness of the material increases, the tool is withdrawn and drops as the thickness, the position of the tool is moved indoors. A non-linear inductive analog sensor with a maximum range of 10 mm, positioned to measure the thickness of the 0-10V supply voltage measurements analog shown in Table 2 using different thicknesses of the room.

As shown, position sensors with analog output nonlinear used in industrial applications must be applied with caution, because the non-linearity, system design and place restrictions on the physical application of the sensor is difficult for use in OEM equipment. Looking at this table, it is clearly a compensation signal processing will be needed to cope with the obvious non-linearity. Because non-linearity in this case non-uniform at both ends of the sensor performs a table is probably easier to implement a compensation equation. Anyway, the developer of PLC code even more complex and the response of the equipment can be reduced only temporary solutions are created to deal with the nonlinear nature of this sensor output.
Simplifying Machine Control Sensors Analog Design “Table 3 linear analog output signal from the remote sensor Source: Eaton ..”

In cases where performance in the picture is not reproducible, then the operating range of the sensor may need to be confined to the central part of the band in an attempt to more “linear” part of the performance curve presented in Table 1. This approach also has its disadvantages, such as sensors in question are often very limited range of detection. If the decision is no longer “linear” part of the nonlinear sensor used in Table 2, the designer has a wide window centered 3 mm to 5.5 mm to cooperate. Managing a small window of this size range may be impossible and the power of the Creator in a sensing technologies completely different.

Reduce complexity
So what is a control system designer to do? Take the example above, but using a sensor with linear output (see Table 3).

In this case, the task of control design is much easier. No lookup table. No fee equation. Simplified PLC logic. And since the range of the sensor can be used, it can be pulled further away from danger. For OEM customers, this means a greater availability machine and a higher throughput and Overall Equipment Effectiveness.

These examples show that linearity is an important characteristic of analog position sensors. Fortunately, a new approach for the design of analog position sensor have produced dramatic improvements in linearity. In addition, technological advances have allowed manufacturers of sensors greatly increased operating distances in the supply of analog devices. Taken together, these improvements in the design allows the designer to control much more flexibility in the implementation of analog sensors on a machine, and serve to reduce the complexity of a system.

My answer was that standard with the VFD pump combination instead of a valve had these advantages:

1. Dramatic reduction in energy costs by eliminating the pressure drop is achieved through the pump;
2. Greater control by eliminating the control valve hysteresis or stickiness;
3. Faster and more responsive flow control valve by eliminating the mechanical action;
4. Elimination of a source of fugitive emissions;
5. Electricity savings from improved power factor of the system.

I have not yet succeeded, these benefits of the VFD anyone actually used this way confirmed.
Barriers

The participants in my survey said the main obstacles to the use of VFD pumps are these:

1. Tradition. “We always use a control valve;
2. The VFD is purchased by a purchaser buys other than the person, the control valves;
3. VFD have a history of unreliable;
4. Our pumps are not designed for use with variable speeds and would be non-linear control use;
5. We have never considered an alternative to a control valve.

The analysis of the benefits

If the energy savings were small, this would be a moot point. However, there are many processes that pumps liquid into the pump to a high head, only to lose that energy, if it appears the pressure drop across a valve, that this source of energy loss up to 25% of that energy to a refinery, chemical or paper mill operation. Even if we designed our processes from the outset with the VFD pumps, we have much smaller electric motors.

There are two factors at work. We know that the flow speed with centrifugal pump speed linear physical laws, which is directly attributable to the perception of non-linearity of paragraph 4. We also know that the electrical current is needed to produce the pump at lower speeds on the main street less than required drive is proportional to the cube of speed ratio. So, by the valve is completely out of the flow path of the amount of stored energy is much larger than one would expect. Of course, less load on the electric motor also means a longer life.

One of the features of the VFD pump combination is the speed of the reaction. Otherwise change the time as the valve in the pressure drop repositioning must stick to the electric motor of the pump to respond within a few cycles of the new spectrum to the new synchronous speed reference work. can react, the speed of the VFD pump to the new current set value so fast that the speed setpoint is ramped necessary to prevent the hammer effect can occur in the process with fluid-filled system when the speed increases.

It is known that the mentioned problem introduced in the tuning of the PID control loops, the variable in the flow loop through the control valve stickiness hysteresis. The valve also leads to a delay caused by mechanical movement of the valve engine. Loops that should be optimized at the factory start-up phase displeased if, the stickiness of the building control valve or the loop to become unstable. In fact, incorporate the latest process control loop auto-tuning software, the actual valve hysteresis compensation up to a point. The loop is detuned gradually, continuing to establish the cause for the process set values ​​for the increased variability due to process upset the flow and pressure control. Today we seem to be that kind of sub-optimal process performance to accept, but we can do better by taking the main source of the error-control valve with a VFD / pump.

The gain from the abolition of the famous fugitive emissions from the packaging of the control valve is clear, if the valve is removed. A less obvious advantage of using a VFD instead of discrete motor starters and electrical switches, operating at a near-linear performance factor. The VFD presents the network as a resistive load with a power factor. When an AC induction motor is placed over the power line, as in a conventional valve position, usually the induction motor is to the power supply with a power factor that can of about 0.7 to 0.9 range range, depending on load and ratings for the engine. This performance means that the amount of electricity consumed by the plant directly to any AC induction motor, the measured power was divided by power connected. In many systems with many of these directly connected three-phase induction motors, which require electric utilities to the use of parasitic capacitances in each phase of the AC cable placed only for the reactive power compensation. Parasitic capacity is required large investments and a constant load on the electrical power plant. Use of VFD eliminates the need for parasitic capacitances because they self-correct for power factor within their own circuits.

The relief valve is a device, usually in a high-low circuit used. The circuit is sometimes referred to as a fast approach, slow feed circuit. The valve is also in a system where a large flow is needed at a lower pressure, and then used later, is a very low flow at a higher pressure is required.

Usually two pumps are plumbed in parallel used in such a circuit.
A fixed displacement pump, the volume provides for low pressure, high flow mode, while a small pump provides the low-flow with the higher pressure. Both pumps have a flow in the low-pressure, high-flow mode. The purpose of the use of two pumps draw energy from the engines to save long term, if only to maintain the function of the hydraulic system at a constant maximum pressure with little or no flow.

If the system cylinders are rapidly expanding at low pressure to send (no pressure relief valve setting), two pumps in its entirety in the cylinder.
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When the cylinder enough to encounter mechanical resistance of the system, the introduction of the relief valve under pressure to be piloted high pump flow directed into the tank through the pressure relief valve. In contrast to a pressure relief valve, reducing the pressure operated valve on the flow is minimal. Therefore, the pressure relief valve no danger to the heating problem. The volume of the smaller pump can not escape to the tank through the relief valve through the check valve in the system. The presence of the valve makes the chart symbol for relief valve differs from a typical pressure relief valve.

When the cylinder further against the resistance (system pressure) is higher than the relief valve setting, the movement is slower than the volume of the small pump to move. In many cases, the cylinder to a halt if the machine is active margins of an assembly machine or system unique. At this point, open the main valve and the maximum (or terminals) pressure. If you’re a safety valve is to be pressure compensated to a maximum pressure limitation of the smaller pump with variable displacement / strain.

In many systems, the large volume, designed to pump pump. The small pump is often used as the pump, since they often used only on a printing system to offer support if the cylinders are used in a terminal mode called. The small pump will only supply enough volume to make the cylinder for an internal leak in the system.

Manual jog control

Jog control allows users to manually step machining. This option can flow through control valves limit or adding a binary triggers are added.

Two-cylinder sequence

 As with any system, it is essential to save the system requirements around the perimeter time and the chance of missing a crucial step reduction.
   The designer should include a clear understanding of the order of operations. This should be a brief description of the machine action with a sketch or drawing. Note pressure, temperature, filtration and other conditions and controls, including manual, auto stop, start, and so on. Then list available input signals of the boundary valves, sensors and other controls. Identify all mechanical and safety interlocks required. Finally, numerical list is a step-by-step sequence of actions, functions and detection method.
   As a final check the circuit operation, an operation to check    while all kinds of events. This includes startup, shutdown, loss of air, panic stops in the middle of the cycle begins    expected mid-cycle and control of any other event.

A selector valve gives the option of one-cycle operation or continuous cycling.

Start options

They usually consist of a series of valves to original equipment distributors. Such systems speed assembly and piping, and all connections between Valves and controls in the circuit are included in the distribution plate design. This saves time and installation design, reducing the number of valves, pipes and eliminates the routing and errors that often go with him.
For example, with discrete air-valve control, a modular system offers in comparison:
• Lower costs for components.
• Simple plumbing and troubleshooting.
• Lower air consumption.
• No air bags.
• A small package.
Compared to electric operation, a modular system provides:
• An explosion protection system with no burnout.
• Reduced power consumption.
• Lower costs by eliminating solenoids and relays.
• A single air supply.
• No heat build up.
Only a few manufacturers offer modular manifold mounted pneumatic control. For instance, Clippard Programmable Controller is a pneumatic sequential Controller, provides step-by-step the operation of the plant.
There is a clear acrylic distributor assembly sequence valves and other components in a compact, efficient package.
The system is designed so that if a task is completed, Feedback will automatically start the next step. Many types of sensors to generate feedback, including Limit valves, proximity switches, pressure sensors, Hall effect switches, pressure sensors and cylinder manual push buttons. Feedback in a positive and safe operation. If no signals (due to a defective, missing or jammed parts, and so on) ends the series and is an indicator of where problems. Internal Locks to prevent out-of-sequence reactions.
An air-operated pneumatic output signal for each step in operation
Equipment, including power-valves, hydraulic valves, pressure switches and other components that can control the air cylinder. The last sequence valve to the system to repeat the cycle of operations.

Pneumatic sequence controller

Replacement of the start button with an AC or selection valve allows continuous cycling.

This is an example of a typical sequence circuit. Most applications require additional features such as delay and prove that the number of sequence Valves, but the procedures for the links and adding
Steps remain the same.
Input signals can come from many devices, including Pressure-reducing valves and feedback devices such as proximity, pressure, Hall effect and liquid-level sensors. The order You can also engage with larger air-end pipes or air-used hydraulic piloted Valves.

System shutoff

To the label of the valve controlling the cylinder with the same letter. Label the pilot valve of the cylinder extends (or activate a device) with a “+” symbol, and moves the pilot valve of the cylinder (or disables a device) with a “-” symbol. Label the line strikes the sensor rod cylinder with the letters on the left (limit valve), the letter of the cylinder, and the position of the sensor for the extension or withdrawal.

Back Pressure Sensing

LVA +, for example, would mean that the border of the enlarged cylinder valve A.
The second step is to display each line of business.
This includes control of action or a step function taking place during this step, and runs the line sensor operation. An example of a simple two-cylinder sequence is shown in the table.
The third step is to select components for the control. Modular systems offer great flexibility, as users can choose from many options in the selection sequence valves.
For example in the “two-cylinder sequence,” for example, five steps – five valves have this sequence – the reset extension and retraction of the two cylinders plus. A foot valve for each step can be used, could choose designer or valves with special functions.

Multiple functions

For example, with the first two steps of a valve which provides a final reset sequence when the start button is pressed or the + LVA limit valve is locked. Reset means the final order is not reset and the bypass valve is actuated.
After selecting the components, it is only a matter of mounting modular fittings and valves in the manifold. Turn on the air and the boundary lines of the valves and electrical connections to the Hall-effect sensors to the inlet connections. And around the air.

Pneumatic valves are currently used in many areas in industrial processes and civic water treatment. These valves are normally automatically by Cabinet conventional power, including terminal distributors, system I / O and communication interfaces via fieldbus.

Each individual in the pneumatic fitting process must be connected to the switch via an air line and a line of discrete Send comments. The cost for planning and installing these solutions are very high, especially in larger and more physically dispersed sites.

automation functions
In many cases, long lines of air traffic control have increased air consumption and a negative effect on the commutation of valves. An alternative to the conventional use of the central network control unit, integration of functions required in the automation of valves themselves. In this case, the process control system is only responsible for supervision and control.

At operational level, are pneumatically operated process used, which can all automation components components are installed as a pilot with manual control, electrical and optical feedback of status indication, including fieldbus faces and even positioners and process controllers.

Plants on the basis of these decentralized systems, distributed automation are working with complete intelligent valve. By integrating the AS-Interface (ASI) as a fieldbus interface, the overall benefits of this approach are fully exploited. All that is necessary for power, feedback and communication is a tie line between the two son PLC with up to 62 valves.

Each valve process is directly connected to the main line in the air, these compounds as short as possible. This reduces the number and length of pipe and cable and the number of required attachments to a minimum.

Valve systems themselves are designed to deployed on the ground in difficult conditions for the robust life of service and long term. Consequently, they have high IP required by the effective implementation and exclusively from weather and chemical resistant materials.

The IP protection is not affected by prolonged use in environments ENVI exposure, high humidity or chemicals. Compared with conventional automation, design marks a real advance towards robustness.

There are other advantages to the reduction of electrical wiring and fewer lines of air traffic control. A status indicator clearly visible in the integrated connector allows the operator to monitor the processes and the operational status of valves not only a central control level, but also directly on the connector.

conventional automation solutions by cabinet, the drivers are used in the factory equipped with an electric feedback. Innovative Valve systems go a step further and restoration for the integration of pilot valves with manual controls, optical position indicators and other functions within the automation stainless steel compact and robust.

Configuration options
Depending on the application, users can choose between different devices and configuration options. The wide range of available options include mechanical switches, inductive proximity switches and NAMUR initiators and indicators of mechanical position and self-final position of linear actuators with inductive sensors move ment.

Basically, distributed on the basis of automation systems intelligent valve begin a process valve with electrical feedback integrated, single optical feedback and integral pilot. These systems already have done with the valve terminals in the enclosures. Moving up a step in the modular program distributors, users can obtain the benefits described above decentralized automation.

In addition to the electrical feedback and the pilot, these solutions include the large size of super-bright colored LEDs for feedback enhanced optical FACIL is monitoring inter-process in the field, and an optional AS-interface as an interface fieldbus with all these functions integrated into the valve system.

The actuator housing is purged with compressed air at each air passage is provided solely controlled by the pilot. This means that after switching, a small volume of control air is supplied into the case. This process takes less than 10 milliseconds and allows a slight pressure builds up in the housing, a new improved protection of intellectual property and preventing the concentration Pene humid air, as in the case of temperature changes or start / immersion.

The pressure relief valve lets you keep backup of pressure in the housing automatically reduced if, after several process switching points, reaching a value of approx. 0.5 bar. The valves meet the same high degree of robustness and process valves.

   The new catalog offers customers a simple, fast way to get the most up-to-date product information, specifications and industry standards.

   Controllers, transducers and relays are ideal for all pneumatic system, the precise regulation of air pressure in pipes and tanks required. Applications include valves, medical diagnostic equipment, web tensioning, roll loading, control panels, pneumatic counter balancers, test and lab apparatus, liquid dispensers, process control, robotics and test equipment.

   The units are in different performance areas of pressure 0-225 psi offered. The port is 1 / 8 “, 1 / 4 “, 1 / 2 “& 3 / 8 ” NPT / BSP. All controls are supplied with 1 / 4 “NPT gauge ports complete. Options include Tamperproof Cover and Factory Preset outlet pressure.

   ControlAir Inc. manufactures precision pneumatic and electro-pneumatic control. ControlAir markets process control, semiconductor, printing and printing presses, diagnostic and surgical medical equipment, robotics, quality control, automotive, analyzers, compressors, pumps and paint equipment.