DISTRIBUTION
Ensure interference-free data communication
Galvanic isolation of circuit components is required in many cases, especially in industrial environments. Capacitive digital isolators can be used to safely and reliably transmit user signals across an isolation barrier. The following circuit example shows how capacitive digital isolators can be used to galvanically isolate remote industrial equipment.
F
or electronics in typical industrial environments, interference-free data communication and personal safety are the two major challenges. Strong electromagnetic high EMC interference are the order of the day. If, for example, the communication cable is laid unfavorably close to a control cable of a frequency inverter, the pulses are capacitively coupled in and the signals in the communication cable oscillate with the pulse pattern of the frequency inverter. This interference can quickly reach a level where endanger the safety of people.
For example, when a thermocouple is used to measure the temperature of a motor, voltages in the millivolt range are generated. If these voltages are transmitted over a cable length of several meters to a central control unit that is referenced to a different ground potential, the measurement signal will be distorted by the potential differences. Summarising the phenomena described, the following four challenges arise:
through the isolator. However, interference and potential equalisation currents are prevented by the galvanic isolation.
Isolated battery voltage measurement
Figure 1: Basic concept of an isolated system for separating different potentials.
• Interference free data transmission • Separation of ground loops between spatial circuits
• Minimise common-mode interference • A safety barrier between hazardous voltages and a user
Figure 1 shows the situation of the data transmission system. In order to meet the requirements of shielding dangerous voltages from the user and still guarantee interference-free data transmission, galvanic isolation must be implemented to separate the zones electrically, i.e. in terms of potential, so that they can work separately and thus
Distributed sensing of physical parameters is the state of the art and powerful microcontrollers facilitate data processing. However, recording the data on the object is often a challenge and wireless transmission of the data is often not possible. The data must be recorded on the object in such a way that to be measured, otherwise measurement errors will occur. This requires electrical decoupling, which must be implemented in the circuitry. Furthermore, the wired transmission of the data must be potential- free and symmetrical so that the transmission is not disturbed by electromagnetic coupling and ground loops. In this application, the use of microcontrollers was deliberately avoided in order to demonstrate that a
Figure 2: Block diagram of the transmitter for potential-free voltage measurement. 6 DECEMBER/JANUARY 2025 | ELECTRONICS FOR ENGINEERS
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