When considering solid-state relays, one should understand the following PhotoMOS relay terminology. The Turn-on time is the time delay until the output of the relay switches ON after an LED current is made to flow through the input terminals. The Turn-off time is the delay from when there is no longer any current flowing through the LED to when the output switches OFF. Having a low On-resistance is important as it reduces power dissipation when switching high currents and increases switching speeds to improve the precision of measurement. Utilizing a relay that has low On-Resistance will minimize the effects of temperature drift. Off-state leakage current is the amount of current flowing across the output terminals when a designated supply voltage is applied, with no LED current flow (relay off). Due to the nature of being a semiconductor relay, the input and output sides are not completely isolated. Therefore, when the input side is in the Off-state, meaning that no current is being applied to the LED, there is still some leakage current flowing through the output. Optically-isolated relays do still offer a true physical separation of the input and output, and the best of these products use a double mold insulation structure which can have an isolation voltage as high as 5,000 VAC. Physical isolation between the relay’s input and output, or between different output channels also enhances precision by minimizing noise.