Why does one of these two Siemens 24V power supply modules have a red light while the other has a green light?

This is a redundant module; if the red light is on, it may indicate that the voltage is insufficient. There is an adjustment button nearby – try measuring and adjusting it with a multimeter

I measured the voltage, and it was 23.5V everywhere

This post was last edited by ZhiGE on 2020-7-21 at 17:07. 1. The PSE202U is a redundant power supply module, with two 24V supplies from SITOP fed into the PSE202U. At least one of these two voltage paths is below the threshold of the PSE202U, which results in an error. 2. Verify whether the threshold voltage setting is appropriate, and measure the power supply output voltages of the two circuits. If all requirements are met (24V minus 0.3V), then it is the threshold voltage that is too high; reducing the threshold voltage of the PSE202U (there is a potentiometer for this purpose) will solve the issue. 3. If the output voltage of a certain power supply is low, adjust the power supply’s output voltage.

Teacher, the measured input voltage is basically 23.95V, while the output voltage is 23.75V. What is the function of the threshold voltage of PSE202U? I rotated the PSE202U button, and indeed the red light turned green; what are the consequences if it remains red?

This post was last edited by ZhiGE on 2020-7-22 at 17:15. 1. If the red light on the PSE202U is on, the output may still be normal and there is no immediate impact on the operation of the devices being powered; however, this indicates a fault or abnormal condition in the power supply module. For example, if the threshold settings for the PSE202U are correct, the presence of the red light indicates that the voltage of one or two power supplies is low. On the one hand, if the voltages of both power supplies are low, the output voltage will also be low. If the load current is high, the line losses will increase, and the voltage that reaches the device may end up being lower than what it requires, resulting in abnormal operation of the device ； Secondly, there may be a power supply failure, resulting in an output below the threshold; only one power supply is operating, which eliminates redundancy and reduces reliability. 2. Once the red light comes on, the cause should be identified and resolved promptly; otherwise, reliable power supply cannot be ensured. 3. The status auxiliary contacts of the power supply and redundant modules are not connected to the DCS control system for monitoring; it is difficult to detect power supply failures through routine inspections. It is recommended to implement such a solution in order to improve the timeliness and effectiveness of fault detection.