In industrial production, in order to increase the loading capacity of the equipment and ensure that the equipment connected to the same signal does not interfere with each other, and to improve the safety performance of electric control, it is necessary to collect, calculate, isolate and amplify the voltage, current, frequency, resistance and other signals output by instruments or sensors , After conversion, transmission and interference removal processing, the industry-wide standard analog current or voltage signal is obtained, and it is safely sent to the secondary instrument or PLC/DCS/PC for use. Users who use analog signal isolators/isolation amplifiers/isolation transmitters/data collectors and other products sometimes encounter technical problems such as field signal matching, load matching, high-frequency interference, multi-channel signal interference, or active and passive, 2/3/4 wire system, loop feeding, etc. selection and application method issues.
As a domestic senior analog signal technology application research and development manufacturer, Sunyuan Technology, based on years of R&D and production experience and extensively collected by technical service engineers, provides valuable feedback from users in various environments on the industrial site. While improving the various technical indicators, we will record and collect some technical problems encountered by engineers on site, hoping to provide users with some technical references and on-site application solutions support. In the future, if we collect more solutions to technical problems, we will update the information in time. Users are welcome to send any problems or complaints and suggestions encountered in the field application to our company's technical support
Signal Isolators: Load Capacity, Operating Principle and Power Options
Signal isolators help reduce ground-loop interference and match sensor outputs to industrial control inputs. Correct selection depends on the signal type, connected load and available power supply.
Output Load Requirements
| Product Type | Current Output: 0–20 mA / 4–20 mA | Voltage Output | Passive isolator / transmitter | Typical load: 250 Ω; selected models support up to 700 Ω with a 24 VDC loop supply | Minimum load resistance: 5 kΩ for 0–2.5 V / 0–5 V outputs |
| Active isolation amplifier / transmitter | Typical load: 350 Ω; specified maximum at 20 mA: 750 Ω for magnetic isolation models or 600 Ω for optical isolation models | Minimum load resistance: 2 kΩ for 0–5 V / 0–10 V outputs |
These values vary by model. Custom load capabilities and higher-current outputs, such as 0–500 mA or 0–1 A, are available on request.
How Signal Isolation Works
The input signal is modulated, transferred across an optical or magnetic isolation barrier, and reconstructed at the output. Depending on the model, the circuit also converts current, voltage, temperature, frequency or other measurements into the required output format.
Isolation helps reduce ground-loop currents and interference from equipment such as variable-frequency drives and solenoid valves. Selected active models provide 3,000 VDC three-port isolation between input, output and auxiliary power. DIN35 mounting simplifies cabinet installation.
Passive or Active: Which Should You Choose?
Passive products draw operating energy from the input or output signal loop and require no separate auxiliary supply. Selection must account for loop voltage and total load.
Active products use a dedicated auxiliary supply and can provide separate input, output and power domains. They are suitable where the required conversion or output-driving capability exceeds the available loop power.
