Elektor Magazine's learn – design – share cycle will rise. We do it by . 4 January & February itouchblog.de controllers to limit the current to 20 mA, many series strings of three LEDs with .. ClarkConnect ClearOS. THE mA CURRENT LOOP. The OmA current loop has been with us for so long that it's become rather taken for granted in the industrial and process. theBear, clarkconnect? that nightmare of a shitty half-assed so-called distro designed to halfass . emolatur, I trust Dell's literature as to what's currently in there. .. Wetmelon, I'm actually looking for 4 20kw BLDCs or PMACs .. electrostatic, so, will you be using a magnetically large loop instead of small?.
Fundamentals, System Design, and Setup for the 4 to 20 mA Current Loop - National Instruments
In electrical signalling an analog current loop is used where a device must be monitored or controlled remotely over a pair of conductors. Only one current level can be present at any time. They are also used to transmit controller outputs to the modulating field devices such as control valves. These loops have the advantages of simplicity and noise immunity, and have a large international user and equipment supplier base.
These loops are used both for carrying sensor information from field instrumentation, and carrying control signals to the process modulating devices, such as a valve.
Field instrumentation measurements are such as pressuretemperaturelevel, flowpH or other process variables. A current loop can also clarkconnect 4-20ma current loop used to control a valve positioner or other output actuator. Since input terminals of instruments may have one side of the current loop input tied to the chassis ground clarkconnect 4-20ma current loopanalog isolators may be required when connecting several instruments in series.
Depending on the source of current for the loop, devices may be classified as active supplying or "sourcing" power or passive relying on or "sinking" loop power. For clarkconnect 4-20ma current loop, a chart recorder may provide loop power to a pressure transmitter.
The pressure transmitter modulates the current on the loop to send the signal to the strip chart recorder, but does not in itself supply power to the loop and so is passive. Another loop may contain two passive chart recorders, a passive pressure transmitter, and a 24 V battery.
The battery is the active device. Note that a 4-wire instrument has a power supply input separate from the current loop. Panel mount displays and chart recorders are commonly termed 'indicator devices' or 'process monitors'. Several passive indicator 7970 amd mantle may be connected in series, but a loop must have only one transmitter device and only one power source active device.
As the operation of pneumatic valves over motorised valves has many cost and reliability advantages, pneumatic actuation is still an industry standard.
This signal is then fed to the valve actuator or more commonly, a pneumatic positioner. The positioner is a dedicated controller which has a mechanical linkage to the actuator movement. This ensures that problems of friction are overcome and the valve control element moves to the desired position. It also allows the use of higher air pressures for valve actuation. With the development of cheap industrial micro-processors, "smart" valve positioners have become available since the mids and are very popular for new installations.
These include an I to P converter, plus valve position and condition monitoring. These latter are fed back over the current loop to the controller, using such as the HART protocol. Analog current loops were historically occasionally clarkconnect 4-20ma current loop between buildings by dry pairs in telephone cables leased from the local telephone company.
These circuits require end-to-end direct current DC continuity, and unless a dedicated wire pair was hardwired, their use ceased with the introduction of semiconductor switching. DC continuity is not available over a microwave radio, optical fibre, or a multiplexed telephone circuit connection. Basic DC circuit tapota lataretu skype shows that the current is the clarkconnect 4-20ma current loop all along the line.
There are still legacy systems in place using this technology. Discrete control functions can be represented by discrete levels of current sent over a loop.
This would allow multiple control functions to be operated over a single pair of wires. Currents required for a specific function vary from one application or manufacturer to another. There is no specific current opera mini 5 mobile9 app is tied to a single meaning. Some devices, such as two-way radio remote control consoles, can reverse the polarity of currents and can multiplex audio onto a DC current.
These devices can be employed for any remote control need a designer might imagine. For example, a current loop could actuate an evacuation siren or command synchronized traffic signals. Current loop circuits are one possible way used to control radio base stations at distant sites. The two-way radio industry calls this type of remote control DC remote. This name comes from the need for DC circuit continuity between the control point and the radio base station.
A current loop remote control saves the cost of extra pairs of wires between the operating point and the radio transceiver. An alternative type, the tone remoteis more complex but requires only an audio path between control point and base station. For example, a taxi dispatch base station might be physically located on the rooftop of an eight-story building. The taxi company office might be in the basement of a different building nearby.
The office would have a remote control unit that would operate the taxi company base station over a current loop hot 16 challenge tede youtube er. The circuit would normally be over a telephone line or similar wiring. Control function currents come from the remote control console at clarkconnect 4-20ma current loop dispatch office end of a circuit.
In two-way radio use, an idle circuit would normally have no current present. In two-way radio use, radio manufacturers use different currents for specific functions.
Polarities are changed to get more possible functions over a single circuit. For example, imagine one possible scheme where the presence of these currents cause the base station to change state:. This clarkconnect 4-20ma current loop is polarity-sensitive. If a telephone company cable splicer accidentally reversed the conductors, selecting channel 2 would lock the transmitter on. Each current level could close a set of contacts, or operate solid-state logic, at the other end of the circuit.
That contact closure caused a change of state on the controlled device. Some remote control equipment could have options set to allow compatibility between manufacturers. In two-way radio use, AC signals were clarkconnect 4-20ma current loop present on the circuit pair.
If the base station were idle, receive audio would be sent over the line from the base station to the dispatch office. In the presence of a transmit command current, the remote control console would send audio to be transmitted. The voice of the user in the dispatch office would be modulated and superimposed over the DC current that caused the transmitter to operate. From Wikipedia, the free encyclopedia. This article is about an analog electrical signaling scheme. For digital serial communications, see Digital current loop interface.
Using Current to Transmit Transducer Data Industrial-grade transducers commonly use current signals to transmit maila majnu video. This is in contrast to most other transducers, such as thermocouples and resistive strain gages, which use a voltage signal. While voltage-based transducers are sufficient in many environments, current-based transducers are at times preferred.
For instance, the inherent disadvantage of using voltage to transmit signals in an industrial environment is voltage drops over long cable lengths due to wire resistance. You can use high input impedance devices to circumvent signal loss.
However, these devices are sensitive to the noise induced by nearby motors, conveyor belts, and radio transmissions. In theory, all current present at the beginning of a loop must reach the end as demonstrated in Figure 1. Figure 1. This is the basic principle clarkconnect 4-20ma current loop which a current loop operates. Measuring current at any position along a single loop produces the same result. By using current signals and low impedance data acquisition devices, industrial applications benefit from better noise immunity and longer transmission cable lengths.
Current Loop Components The main components of a current loop include a DC power supply, transducer, a data acquisition device, and wires connecting them together in a series, as shown in Figure 2. The DC power supply provides the power to the system.
The transducer regulates the flow of current through the wires at 4 to 20 mA, where 4 mA represents a live zero and 20 mA represents the maximum signal. A 0 mA signal signifies a break in the loop. The data acquisition device measures the regulated current flow. To help better understand current loops, consider the design of an example system using a transducer throughout this white paper.
System specifications include the following:. Choosing a Transducer The first step in designing a current loop system is selecting a transducer. Beyond the type of measurement flow, pressure, temperature, and so onan important consideration in choosing any transducer is the operating voltage. A voltage source provides power to the current-based transducer, allowing it to regulate the flow of current through the wires.
To maintain transducer clarkconnect 4-20ma current loop, the voltage supplied should be no less than the minimum required; likewise, supplying more voltage than the maximum specified can damage the transducer. For the example current loop system, your chosen transducer measures pressure and has an operating voltage of 12 to 30 V.
With the transducer selected, properly measuring the current signal is required to provide an accurate representation of the pressure applied to the transducer.
Choosing a Current Measuring Data Acquisition Device An important aspect of building a current loop system is avoiding ground loops. A common method of preventing ground loops with a measuring clarkconnect 4-20ma current loop acquisition device is isolation. With isolation, you can avoid ground loops such as the one in Figure 3. Ground loops are created when two connected terminals in a circuit are at different ground potentials. This difference causes current to flow in the interconnection, which can produce offset errors.
Isolating the data acquisition device is a means of electrically separating signal source ground from the amplifier ground of the data acquisition device, as shown in Figure 4. Because current cannot flow across the isolation barrier, the amplifier ground reference can be at the same potential as the signal source ground. Thus, you cannot inadvertently create a ground loop. Isolation also prevents large common-mode voltages from damaging data acquisition devices.
Common-mode voltage is the voltage present on both the positive and negative inputs of an instrumentation amplifier. If the data acquisition device has no isolation and the common-mode voltage is outside the maximum input range, you may damage the device. This would be a hazardous voltage level to a data acquisition device with a smaller working voltage.
With isolation, the amplifier ground reference is electrically separated from earth ground. Now the data acquisition device is no longer at risk of overvoltage damage. Note that isolators have a maximum common-mode voltage they can reject. With the current measuring data acquisition device isolated and protected, matching a clarkconnect 4-20ma current loop supply is the last lagu pmr duit duitang in completing a basic current loop system.
Choosing a Power Supply Discovering which power supply best meets your requirements is simple. In a current loop, the power supply must emit voltage equal to or greater than all the voltage drops in the system combined. The data acquisition device for this example uses a precision shunt resistor to measure current. You wasureranneyo to calculate the voltage drop across the resistor.
Implementing basic calculations with the 4 to 20mA current loop shows the following:. The pressure transducer from above requires a minimum operating voltage of 12 V with a maximum of 30 V.
Adding the voltage drop of the precision shunt resistor to the transducer yields clarkconnect 4-20ma current loop following:. This suggests that a 17 V power supply suffices. In applications where a transducer is far away from the measuring instruments, you must factor wire resistance into the loop power calculations. Copper wires have a DC resistance that is directly proportional to their lengths and diameters gauge.
With the pressure transducer from the example system, you need to calculate the ft distance in the power requirements. With gauge solid copper wire, the internal resistance is 2.
This resistance calculation becomes:. At ft away, there is a 1. To complete the loop, you need two wires, effectively doubling the length to ft:. In total, approximately 2. Combining all the voltage drops results in the following:. If you used a 17 V power supply to drive the previous setup, the pressure transducer voltage would be below the minimum operating level for a transducer due to natural wire resistance and shunt resistor requirements.
Choosing a common 24 V power supply meets the power requirement of the pressure transducer system. If desired, there is enough voltage to place the pressure transducer at a further distance. With the transducer, clarkconnect 4-20ma current loop acquisition device, cable lengths, and power supply properly matched, the simple pressure transducer loop system is complete. For larger applications, you can incorporate additional measurements into the system.
Adding More Transducers and Instruments For larger applications, you can add more transducers and instruments in parallel to the power supply, as shown in Figure 5. At times, you may need multiple current measuring data acquisition devices to measure the same signal. To add another data acquisition device to the clarkconnect 4-20ma current loop transducer, you must place the new instrument in series with the particular loop.
For this clarkconnect 4-20ma current loop, you add a simple digital current loop meter with the existing data acquisition device, as shown in Figure 6. Each time you add a current-measuring data acquisition device in series with the transducer, you must recalculate the total voltage requirement to ensure that the power requirements of the loop are still within specification.
Because adding the meter brings the total voltage requirement to only about Also, with newer standards and types of transducers, you can extend the measurement capabilities of existing current loop infrastructures.
Digital signaling developments have broadened the current loop's application space and delivered more functionality to an already robust, low-cost system. With digital signaling, HART-enabled transducers allow responses to proprietary commands to perform certain actions or reply with a status beyond the 4 to 20 mA current signaling.
Using this technology, industrial automation and control applications can actively monitor and respond to situations by communicating between intelligent field instruments and host systems.
Learn more about HART. For specialty applications such as magnetic flowmeters, 3-wire Type 3 and 4-wire Type 4 transducers are also available. Type 3 transducers provide two transducers clarkconnect 4-20ma current loop in one. These transducers are designed and installed in the same manner as the clarkconnect 4-20ma current loop transducers explained in this white paper. Type 4 transducers provide separate connections for power and current measurements.
Because 4-wire transducers decouple power from the measurement system, the need for clarkconnect 4-20ma current loop isolation requirement at the measuring data acquisition device is lifted. A drawback of 4-wire transducers, though, is that the power source requires a separate pair of wires that must run the cabling distance. This causes many applications to place the power source near the transducers. Learn more about Type 3 and Type 4 transducers. Current loops are ideal for industrial environments where long cable lengths are required or large amounts of electromagnetic interference exist between the transducer and data acquisition device.
Whether automating a factory floor or taking field measurements, you can find a variety of National Instruments isolated current measuring devices across different platforms to meet your application needs. Isolation Technologies clarkconnect 4-20ma current loop Reliable Industrial Measurements. Rate this document Select a Rating 1 - Poor 2 3 4 5 - Excellent. Answered Your Question?
With their low implementation cost, inherent resistance to noise, and ability to carry signals long distances, current loops have proven particularly well-suited for industrial environments. This white paper focuses on current loop fundamentals, system design, and setup. Figure 2. System specifications include lie to me episodes from amazon following: Transducer needs to measure pressure Transducer is located ft away from the measurement device A current measuring the data acquisition device provides an operator with feedback about the transducer measurements This example begins with determining an appropriate transducer for the application.
Designing a Current Loop System Choosing a Transducer The first step in designing a current clarkconnect 4-20ma current loop system is selecting a transducer. Figure 3. Ground Loop Ground loops are created when two connected terminals in a circuit are at different ground potentials.
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