What is a typical output from a temperature controller?

A typical output from a temperature controller is a 4-20 mA current signal. This output format is widely used in industrial automation and control systems because of its advantages in long-distance transmission and noise immunity. The 4-20 mA signal allows for a clear representation of the process variable—in this case, temperature—where 4 mA typically indicates the lower range of the measurement and 20 mA the upper limit. This range provides a built-in failure detection mechanism; if the current falls below 4 mA, it often indicates a fault within the system, such as a broken sensor or cable.

In contrast, other options have their specific applications but are not typically as standard for temperature controllers. For example, a 0-10 V voltage signal can also be used for control, but it is less common compared to the 4-20 mA standard in many environments where distance and interference are concerns. A digital on/off signal is typically used for simple control logic rather than proportional temperature control, which is more complex and requires a continuous signal. Lastly, a variable frequency signal is often associated with controlling motors or fans rather than directly indicating temperature, thus making it unsuitable for typical temperature controller outputs.