Complete Guide to Selecting Current Transformer (CT) & Current Transducer
In modern industrial automation systems like PLC, DCS, and SCADA, accurate current measurement is essential for monitoring motors, energy consumption, and process control.
Two important devices are used for this purpose:
- Current Transformer (CT)
- Current Transducer
Before purchasing these devices, engineers must evaluate several major and minor specifications to ensure accuracy, reliability, and safety.
Download Complete CT & Current Transducer Specification Guide
This guide includes all important engineering parameters such as CT ratio, accuracy class, burden rating, isolation, output signal types, and compatibility with PLC/DCS systems.
⬇ Download PDF GuideMajor Specifications for Current Transformer (CT)
| Specification | Description | Example |
|---|---|---|
| Primary Current | Maximum current flowing in the conductor | 100A, 200A, 400A |
| Secondary Current | Standard output current of CT | 5A or 1A |
| CT Ratio | Primary to secondary current conversion | 200/5, 400/5 |
| Accuracy Class | Measurement accuracy | 0.2, 0.5, 1.0 |
| Burden Rating | Maximum load connected to CT secondary | 5VA, 10VA |
| Frequency | Operating frequency | 50Hz / 60Hz |
| Insulation Level | Voltage insulation capability | 0.72kV, 3.3kV |
| Short Time Current | Fault current withstand capability | 20kA for 1 second |
Minor / Mechanical Specifications for CT
- Mounting type (Ring type / Busbar type)
- Window size for cable or conductor
- Terminal type (Stud / Screw)
- Operating temperature range
- Material quality (Epoxy resin / molded case)
- Protection rating (IP rating)
Major Specifications for Current Transducer
| Specification | Description | Example |
|---|---|---|
| Input Current | Current from CT secondary | 0-5A or 0-1A |
| Output Signal | Signal sent to PLC/DCS | 4-20mA or 0-10V |
| Accuracy | Conversion accuracy | 0.2%, 0.5% |
| Supply Voltage | Power supply required | 24V DC |
| Isolation | Electrical isolation protection | 2kV isolation |
| Response Time | Speed of signal conversion | <200 ms |
| Linearity | Signal proportionality | ±0.1% |
Minor Specifications for Current Transducer
- DIN rail or panel mounting
- Configuration method (DIP switch / software)
- Temperature operating range
- Long-term signal stability
- Calibration capability
- Protection against overcurrent
Important Safety Rules
- Never leave CT secondary open.
- Always short CT before disconnecting load.
- Ensure proper grounding.
- Verify insulation ratings.
Conclusion
Choosing the correct Current Transformer and Current Transducer ensures accurate current monitoring, protects electrical equipment, and improves reliability of PLC and DCS systems. Engineers should always verify both electrical and mechanical specifications before purchasing instrumentation devices.