Today, Wuxi Rihuan Sensor Technology Co., Ltd. will introduce to you the three-step troubleshooting method for "sensor indicator light is on but there is no output". 

During on-site maintenance, a common situation is encountered: the indicator light of the sensor is normally illuminated, but there is no signal at the output end, and the load does not operate. At this point, there is no need to rush to replace the sensor. Instead, you can follow these three steps to conduct a step-by-step investigation. 

Step 1: Check power supply

Confirm whether the sensor's power supply voltage is within the product's specified range (commonly DC 24V). Pay attention to the connection method of the common terminal of NPN and PNP outputs: for NPN type, the load's common terminal is connected to the positive pole of the power supply; for PNP type, the load's common terminal is connected to the negative pole of the power supply. If the ground wire at the site is disconnected, the indicator light may light up, but the output drive current is insufficient, and the load cannot work properly. 

Step 2: Check wiring compatibility

Check for any open circuits or poor connections in the output wires. Specifically, confirm whether the output type of the sensor matches the input port of the PLC: 

The NPN output should be connected to the SINK-type input port of the PLC (with low level as the valid signal). 

The PNP output should be connected to the SOURCE type input port of the PLC (with high level as the valid signal). 

Mixing of types will cause the PLC to fail to recognize the signal. 

Step 3: Check the load capacity

The output driving current of the sensor is generally no more than 100mA. It is fine to directly drive a small relay, but if you try to drive the coil of a large contactor, the starting current may exceed the rated value of the sensor, causing the output voltage to drop sharply, creating the false appearance of "the indicator light is on but the load does not operate". The solution is to add an intermediate relay between the sensor and the large load for isolation. 

After completing these three steps, if the fault persists, then the possibility of damage to the sensor's internal components should be considered. 

Each sensor of Rihuan Sensing undergoes full-load testing before leaving the factory. The output parameters are accurate and reliable, and it is easy to match with various PLC input ports. Welcome to pay attention to Rihuan Sensing to obtain stable and reliable sensor products.