Which device emits pulses for variable flow rate chemical injection?

The correct choice is the dry contact water meter. This device is specifically designed to measure the flow rate of water and can emit pulses based on the measured flow. The pulses are then used for various applications, including controlling systems that inject chemicals into the water supply.

Dry contact water meters output signals that can be used to trigger other devices, such as chemical injectors, based on the amount of water flowing. This allows for precise control over chemical dosing depending on the flow rate, which is essential in maintaining the right chemical balance in water treatment processes.

In contrast, a flow regulator primarily manages the distribution of flow without necessarily generating pulse output, and a flow meter, while it measures flow, does not specifically pertain to variable flow rate chemical injection, as it may not always provide the pulse function needed for such applications. The chemical injector itself is responsible for integrating with these systems to inject the chemicals but does not emit pulses; it acts on signals received from meters or control systems.