What is the difference between isolated and non-isolated voltage?

Isolated versus non-isolated voltage refers to the connection (or lack thereof) between the input supply voltage ground and output signal ground on voltage output transmitters, typically located within the DC/DC converter. In isolated voltage sensors, a transformer is used to create a barrier between the common mode voltage (CMV) ground of an instrumentation system and the output ground. This creates a level of human safety in high CMV systems as well as inherent overvoltage protection to instrumentation in all types of systems, especially in the event of accidental overvoltage to the sensor. It also provides differential signal consistency. Power spikes or voltage fluctuations can pass through the sensor and into the data acquisition portion of instrumentation systems when input/output isolation is not used.