Glossary · Process instrumentation and analytical measurement
Signal isolator
Also known as: Isolating converter, Loop isolator
German: Signaltrenner
In instrumentation, a signal isolator is a device that galvanically separates the input and output circuits of an analog or digital signal while transferring the signal, to break ground loops, protect equipment and connect circuits at different potentials.
- Process instrumentation
In one sentence
A signal isolator galvanically separates two signal circuits while passing the signal on, breaking ground loops and protecting inputs.
Example
A loop-powered signal isolator separates the 4–20 mA signal of a field transmitter from the input of a third-party controller that has a different ground reference.
How it applies
- Engineering: Signal isolators are needed when two systems with different grounds share a signal, when one signal is fed to several devices, or when interference must be kept out. Loop-powered versions need no separate supply but add a voltage drop.
- Installation: Check the isolation voltage and whether input and output are active or passive, so the loop is powered exactly once.
- Explosion protection: Isolators with Ex i circuits can serve as associated apparatus; their certificate data then belong to the intrinsic safety assessment.
- Documentation: Mark isolators in loop diagrams and terminal plans, including the loop voltage drop where relevant.
Signal isolator vs. isolation amplifier
The terms are largely interchangeable. Isolation amplifier suggests additional signal processing, while signal isolator focuses on the isolation.