It acts like a current loop isolator up to a point but doesn’t use a transformer or optocoupler for isolation! Maybe we could call it a “non-galvanic isolator” but we can’t think of any other type of isolation other than galvanic. Since it tolerates ground differential voltages up to 120V we even considered naming it “The Tolerator” but to avoid controversy we opted for “Ground Loop Filter” or “GLF” for short. This module interfaces a field transmitter producing 4-20mA to a PLC or DCS input. Where analog isolators can provide optical or transformer isolation up to 2KV or higher the Emphatec InstaLink-GLF provides a very high impedance between the input and output loops but does not actually isolate the signals.

This acts as a barrier for currents caused by ground differentials. The barrier is rated 120V - above 140V it can break down and a ground loop current would be produced. 120 volts represents a sizeable ground differential voltage and much lower values are typical.

A unique feature of the Emphatec InstaLink-GLF is the make-before-break connector that allows a meter to be inserted into the input loop and removed without causing a momentary interruption of the loop. This makes calibration very easy. A test cable is available. Other features include very fast response time and plug-in jumpers for easy distribution of 24Vdc (included with each module). Best of all, the low price allows you to install one in each of your current loops as insurance against errors caused by ground loops. If you are only concerned with ground loops the Emphatec InstaLink-GLF is the solution. If you are also trying to prevent overvoltage transients from reaching your PLC or DCS then the Emphatec InstaLink-CLI isolator might be a better solution.