Digital Input Device Not Registering on NI-9411 Module

Issue Details

The NI-9411 digital input module successfully detects signals from the NCB1,5-8GM25-N0 sensor (NAMUR type), but fails to register input from the NBB1,5-8GM40-Z0 sensor.

Solution

To resolve the issue, it is recommended to replace the NBB1,5-8GM40-Z0 sensor with a NAMUR-type sensor such as the NCB1,5-8GM25-N0, or any other sensor that meets the NI-9411’s input voltage requirements.

This recommendation is based on the electrical behavior of the sensors:

• Both the NBB1,5-8GM40-Z0 and NCB1,5-8GM25-N0 sensors output approximately 3.5 V when the sensor is open (no target detected).
• However, the NBB1,5-8GM40-Z0 sensor maintains this voltage level regardless of switching state, which does not drop below the NI-9411’s LOW threshold of 0.8 V, making it unsuitable for reliable state detection.
• In contrast, the NCB1,5-8GM25-N0 (NAMUR type) sensor uses a current-based signaling method. When the sensor switches to the LOW state (target detected), the internal circuitry causes the voltage to drop to ~0.5 V, which falls within the NI-9411’s LOW input range (0–0.8 V).