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PLC: Difference between Open Collector and Line Driver

FAQ No. FAQ01119

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Question

What is the difference between the open collector and line driver used with a High-speed Counter Unit?

Answer

The encoder specifications determine if an open collector or line driver is needed. Generally the open collector and line driver have the following characteristics.

Open Collector

The open collector operates depending on whether standard voltage is high or low compared to the input voltage. The effect of noise will cause the open collector signal to turn ON or OFF. Noise immunity can be improved by shortening the cable distance, using a shielded cable, or by using a capacitor.

Line Driver

The differential line driver sends a reference voltage along with the voltage as a signal. Because the noise is spread across two lines (both the positive and negative sides), even if there is noise on the cable, the input circuit will not be easily affected. In environments that are easily affected by noise or situations in which the distance the cable must travel is great, it is useful to use a line driver.