Nanjing Paroken Technology Co., Ltd. Working principle:
First, the signal from the transmitter or instrument is modulated and converted using semiconductor devices, then isolated and further converted via optical or magnetic sensing elements, and finally demodulated back to the original signal prior to isolation. Simultaneously, the power supply for the isolated signal is also isolated, ensuring absolute electrical independence among the transformed signal, the power supply, and the ground.
Function:
1. Protect the control circuit of the lower-level device.
2. Mitigate the impact of environmental noise on the test circuit.
3. Suppress interference to equipment caused by common-ground currents, variable-frequency drives, solenoid valves, and unidentified pulse signals; at the same time, provide voltage-limiting and overcurrent protection for downstream devices, thereby offering reliable protection for the input/output and communication interfaces of transmitters, instruments, variable-frequency drives, solenoid valves, and PLC/DCS systems.
The standard-series rail-mounted structure is easy to install and effectively isolates the potential between the input, output, power supply, and ground. It can mitigate inverter noise and various high- and low-frequency pulsating interferences. The main types of signal isolators include:
1) Isolator: ( PA-1187)
In industrial production, to increase the load-carrying capacity of instruments, ensure that instruments connected to the same signal do not interfere with one another, and enhance electrical safety, it is necessary to acquire, amplify, process, and perform anti-interference treatment on input signals such as voltage, current, frequency, and resistance, and then output isolated current and voltage signals that can be safely transmitted to secondary instruments or PLC/DCS systems.
2) Distribution device: ( PA-1317)
Industrial field applications typically employ a two-wire transmission scheme, which not only supplies a 24 V power source to primary instruments such as transmitters but also acquires, amplifies, processes, and filters the incoming current signal to eliminate interference, before outputting isolated current and voltage signals for use by downstream secondary instruments or other instrumentation.
3) Safety Barrier: ( PRG-1100)
Certain specialized industrial environments—such as gas utilities and chemical plants—not only require two-wire transmission that provides both power distribution and signal isolation, but also demand intrinsically safe, spark-proof explosion protection. This involves reliably limiting power supply output to prevent ignition between the power supply, signal lines, and ground; implementing dual current-limiting and voltage-reducing measures to restrict both signal and power circuits; and ensuring that the energy entering hazardous areas remains within safe limits. What precautions should be taken during the installation and maintenance of signal isolators?
Although isolation devices vary in manufacturing processes and wiring configurations depending on the manufacturer, their typical applications are essentially the same; therefore, the requirements for product protection and maintenance are also largely identical.
1. Read the instruction manual carefully before use.
2. When used for signal isolation, the input terminal shall be connected in series with the loop circuit, and the output terminal shall be connected to the sampling loop.
3. When used for isolated power distribution, the input terminal shall be connected to the power supply circuit, and the output terminal shall be connected to the transmitter.
4. If the system is not operating normally, first check that the wiring is correct and verify that the power supply is present and that the polarity is correct. Sometimes the field signals received by the PLC exhibit large errors and poor stability.
There are many reasons for this phenomenon, with the potential difference between the reference points of different instrument signals being a key factor. This “difference” gives rise to interference currents among the instrument signals, leading to large errors and poor stability in the PLC. Therefore, it is optimal for the signals from different devices and instruments to share a common reference point. Isolators provide complete electrical isolation between the input and output, thereby establishing a common reference point on the PLC’s analog interface board and resolving the problem under ideal conditions. However, if we isolate the 4–20 mA channels but there is no available space in the control cabinet to accommodate a power supply, what should be done?
A kind Passive Signal Isolator It can achieve 4–20 mA signal isolation without requiring an external power supply. With so many brands of isolators available on the market today, each offering a wide range of prices, how should you make your selection?
Isolators are positioned between two system channels; therefore, when selecting an isolator, the first step is to define its input–output functionality and ensure that its input–output mode (voltage-based, current-based, loop-powered, etc.) is compatible with the interface modes of the upstream and downstream channels. In addition, numerous other critical parameters—such as accuracy, power consumption, noise performance, insulation strength, and bus communication capabilities—significantly influence product performance. For example, noise is closely related to accuracy, while power consumption and heat dissipation affect reliability; these factors must be carefully considered by the user. In summary, suitability, reliability, and cost-effectiveness are the primary criteria for selecting an isolator.
The DCS is receiving unstable signals from the field-mounted two-wire pressure transmitters. How can this be resolved?
Two-wire transmitters are widely used in industrial automation. Like other field devices, they are susceptible to interference and must therefore be designed with effective anti-interference measures. Depending on the DCS analog input card’s interface type—either current-based or loop-powered—a suitable isolation power supply unit should be selected; in principle, this device must both provide isolated power to each transmitter, ensuring that every transmitter has its own independent power supply, and isolate and transmit the transmitter signals to the DCS. PLC analog input cards typically operate on a two-wire loop-powered configuration and also require signal isolation. Under these circumstances, how should the appropriate product be chosen?
Two-wire loop power supply is a common analog interface. Products designed for this interface are referred to as the two-wire loop-isolated product series. In such isolation transmitters, all internal isolation components employ transformer-based isolation: on the one hand, they transmit the signal, and on the other, they transfer electrical power from the supply side to the input section, ensuring that the various circuits in the input section operate normally.