Encoder does not count fault resolution - Database & Sql Blog Articles

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Recently, a colleague reached out to me with an issue they were facing. They mentioned that their encoders often failed to output any data, and the problem was that the encoder readings remained fixed at a constant value, without updating. The encoder in question is a Turck incremental encoder, and it's connected to an FM450-1 module. The wiring setup includes 1A*, 1B*, 1N*, 1M, and DC24V. The 24V power for the module comes from an external Phoenix power supply.

The colleague had already replaced the encoder, the module, and the cables, and confirmed that the 24V power supply was functioning properly during the fault. Since the device itself seemed fine, we started looking into possible grounding or interference issues. I recalled a similar situation I had encountered before, where improper signal levels caused the encoder to malfunction.

I checked the manual for the FM450-1 module and found a critical note: "The circuit of the counter input (encoder power supply, encoder signal) is electrically isolated from the CPU ground. Therefore, terminal 4 (1M) must be connected to the CPU ground with low impedance!" This made me think—maybe the issue was related to how the encoder power was grounded.

So, we decided to measure the voltage of the encoder power supply relative to the CPU ground during both normal operation and when the fault occurred. The results showed that under the faulty condition, the voltage was only around 10V, which was insufficient for the module to recognize the encoder signal. As a result, the system wasn't counting properly.

After connecting terminal 4 (1M) directly to the CPU ground, the issue was resolved. The encoder began working as expected, and the system started counting again. This experience reinforced the importance of proper grounding, especially when dealing with isolated circuits like those found in encoder interfaces.