Voltage, current, temperature, pressure, strain, and flow measurements are an integral part of industrial and process control applications. Often these applications involve environments with hazardous voltages, transient signals, common-mode voltages, and fluctuating ground potentials capable of damaging measurement systems and ruining measurement accuracy. To overcome these challenges, measurement systems designed for industrial applications make use of electrical isolation.
Features and Benefits
Isolation electrically separates the sensor signals, which can be exposed to hazardous voltages, from the measurement system's low-voltage backplane. Isolation offers many benefits including:
- Protection for expensive equipment, the user, and data from transient voltages
- Improved noise immunity
- Ground loop removal
- Increased common-mode voltage rejection
Needs for Isolation
Consider isolation for measurement systems that involve any of the following
- Vicinity to hazardous voltages
- Industrial environments with possibility of transient voltages
- Environments with common mode voltage or fluctuating ground potentials
- Electrically noisy environments such as those with industrial motors
- Transient sensitive applications where it is imperative to prevent voltage spikes from being transmitted through the measurement system
Methods of Implementation
LEDs produce light when a voltage is applied across them. Optical isolation uses an LED along with a photo-detector device to transmit signals across an isolation barrier using light as the method of data translation. A photo-detector receives the light transmitted by the LED and converts it back to the original signal.
Inductive isolation uses a pair of coils separated by a layer of insulation. Insulation prevents any physical signal transmission. Signals can be transmitted by varying current flowing through one of the coils, which causes a similar current to be induced in the second coil across the insulation barrier. Inductive isolation can provide high-speed transmission similar to capacitive techniques. Because inductive coupling involves the use of magnetic fields for data transmission, it can be susceptible to interference from external magnetic fields.