Signal isolators are used to connect a grounded signal source to a grounded signal follower. If the speed control input of an adjustable frequency drive is grounded, any input signal must be ungrounded. A signal isolator provides electrical (galvanic) isolation between the input and output circuits. It converts the input into a frequency and then couples the signal to the output through a transformer or optical isolator. Signal isolators also break the direct electrical (galvanic) path between two or more loop points. They are used to protect against dangerous measured-variable voltages and provide increased protection from surges and spikes.