From the course: Input Sensors with PLC: 4-20 mA Current Loop

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Why start from 4 mA instead of 0 mA?

Why start from 4 mA instead of 0 mA?

From the course: Input Sensors with PLC: 4-20 mA Current Loop

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Why start from 4 mA instead of 0 mA?

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- [Instructor] Now a question is why choosing four milliamps as the starting point instead, for example, zero milliamps? One of the good practices when working with industrial measurements and signal ranges is to avoid choosing real zero as the start point. The reason for it is to differentiate between an actual zero reading and a device failure, which is helpful in troubleshooting and fault detection. For example, when the sensor has failed or disconnected, or in a case of any loose or broken wires or open circuit, the transmitter will produce a zero milliamps. If we choose real zero as our starting point, then we wouldn't know if zero milliamps is the minimum value being measured or there is a failure or loose connection. So having a four milliamps output for 0% of the sensor range makes it simple to detect a fault in the system. The four milliamps here is called a live zero. The term live zero is used to describe a signal…

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