What is the primary signal source in an electrical resistance-type temperature indicating system?

In an electrical resistance-type temperature indicating system, the primary signal source is a temperature bulb or sensing element. This component functions by responding to temperature changes and consequently altering its resistance. As the temperature increases or decreases, the resistance of the sensing element changes, producing a corresponding electrical signal that can be read by the associated instrumentation, such as a temperature gauge.

The temperature bulb or sensing element is essential because it directly measures the temperature of the environment or fluid it is in contact with and translates that physical measurement into a measurable electrical signal. This results in accurate temperature readings for monitoring and control within various applications.

While other components like thermocouples, temperature gauges, and electrical sensors also play roles in temperature measurement systems, they do not act as the primary signal source in a resistance-type system. Each of these options serves a different purpose or operates on different principles, but it is the temperature bulb or sensing element that specifically governs the resistance changes necessary for the function of this type of indicating system.