The fixed resistance means the resistance value does not change much under the influence of external conditions. Fixed resistors have a nominal resistance, which is usually marked on the resistor. In many devices, fixed resistors are used. A fixed resistor is connected to the coil of the PLC output. This fixed resistor is also called freewheeling resistor or a bleeder resistor. The current resistance is used to consume the self-induced electromotive force generated at the moment of power-off. The fixed resistor also acts as a shunt when energized.
We know that fixed resistors are used most in cableway electrical systems. Many times fixed resistors are used in series with other components. The PLC output controls various indicators, and a fixed resistor is connected in series in front of the LED anode. The current of the LED is normal when the LED is working normally. The operating current of the low-power LED is generally between 5-30mA. If the current flowing is too large, It is easy to be burned, and the normal working voltage is also low.
According to the characteristics of the series circuit, when the currents are equal everywhere, the total voltage is equal to the sum of the voltages everywhere, and the total resistance is equal to the sum of the resistors. Therefore, it can be known that the fixed resistor here acts as a step-down and current limiting function. Let the voltage at both ends of the LED and the current flowing through it be within the rated working range to ensure that the LED can work normally without being damaged.

Fixed resistors are used for buck and current limiting in PLC devices. Many times we use them with other electronic components to achieve the best results. When the voltage is too high or the current is too large, the fixed resistor can protect the current well, avoiding damage to other electronic components in the current or the circuit can not work.