Conventional transmitters require circuit power supply – how do the AI cards in DCS/PLC achieve this?

The AI (analog input) cards of DCS (distributed control systems) or PLCs (programmable logic controllers) usually require an external power supply. These cards generally do not generate their own power supply; instead, they rely on an external power source to provide the electricity needed for the sensors or transmitters. Specifically, there are two common ways to achieve this type of power supply: 1. The card itself outputs power: Some AI cards are designed to be able to provide a certain voltage, usually 24VDC. The channels of these cards can supply power to the connected sensors or transmitters. This approach reduces the need for external power supplies and jumpers, as the power supply and signals are connected on the same card. 2. External power supply: Another method is to use an external power source to power the sensor or transmitter. In this case, the channels of the AI card do not provide power; instead, they only receive analog signals from sensors or transmitters. This usually requires the use of an external power supply module and appropriate jumpers to provide the necessary power to each sensor or transmitter. Which method is better depends on the specific application and system requirements. Generally, using the power supply provided by the card itself is simpler, as it eliminates the need for an external power source and connection cables, but it may be limited by the current output of the card. If a higher current supply is required or there are other special requirements, it may be more appropriate to use an external power source. Therefore, the appropriate method should be selected based on the power requirements of the specific application and the system design. .

2. When an external power source is used, does the circuit become a non-isolated circuit, making it more susceptible to external interference?