Isolator Function

Select products that include an Isolation function.

Find Isolator select ⇒ Input ⇒ Output

Select products that include an Isolation function.

Isolator Function

A Signal Isolator is a Signal transmitter with Isolation

Isolation is the electrical separation of two circuits such that there is no electron flow between the two circuits.

Signal Isolation

Isolation is one of the most critical issues in process control. It is used to prevent unwanted current loops, ground loops, protection of delicate equipment and ensuring the safety of human operators when high common mode voltages are to be expected.

Isolation is the electrical separation of two circuits such that there is no electron flow between the two circuits. The isolation breakdown voltage defined for such equipment, is the voltage required to cause flash-over or a breakdown in isolation, in such a circuit.

Isolation in general purpose analogue circuits is usually achieved by passing signal over a barrier using magnetic or optical coupling then converting the signal to the required output type.

There are usually three isolation paths to be considered; supply to input, supply to output and input to output.

Signal powered isolators provide isolation for the input / output and output / supply paths, but not for the input / supply path (as the signal is the supply).
Loop powered isolators provide isolation for the input / output and input / supply paths, but not for the output / supply path.
Only a 4-wire or separately powered transmitter will provide true 3-way galvanic isolation will isolate all three paths.

The need for Isolation

In most processes there are pieces of electronic measurement and control equipment from many different manufactures. The signals from these instruments are interconnected to each other and to sensors, transducers and output devices connected in the process loop. In any such measurement and control system there are several problems that are likely to occur, all of which can be solved by incorporating the appropriate isolation between signals.

Proper isolation should be of the highest priority in process control systems. Used correctly isolation will prevent unwanted current loops, ground loops, damage to delicate equipment and ensure the safety of human operators when high common mode voltages are to be expected.

Common Ground Loop Problems

This type of fault occurs when the return path of least resistance for the signal is via the earth or ground. An example of this type of fault is when measuring the pH of a liquid and the liquid has a return path to a grounded power supply.

It must be remembered that if the measurement is not isolated the return path could be through any one of the instruments connected to the same plant.

Common Ground Loop Problem

Common Current Loops Problems

Common Current Loop Problem

A current looping problem will arise whenever the path of least resistance for the output loop current is not the intended path.

A classic example of this is shown below, the two receiving instruments are supplied from the same 24Vdc supply and have a common input and supply negative.

In this illustration the current flows into Rec Inst. 1 where it finds the path of least resistance to return to the supply ground is return via the Rec Inst. 1 negative supply rail, thus bypassing the input of Rec Inst. 2.

Common Floating Voltage Problems

Dangerous high voltages can be present at sensor level, as in the case with a dc shunt. This voltage will be conducted through a non-isolated transmitter creating a threat to humans with a floating load or damage to receiving devices.

Common Floating Voltage Problem

Common Mode Noise

Often the signals from sensors and transducers are small voltages and susceptible to noise pick-up from motors, variable speed drives and general switching spikes carried by the electrical reticulation system.

If there is isolation between input and output, the common mode noise (present on both input terminals with reference to ground) will be prevented from passing to the output even if it is relatively high in magnitude.