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Electrician Red Seal · Question

An electrician is commissioning a new level control system. The ultrasonic level sensor provides a 4-20 mA output, where 4 mA corresponds to an empty tank (0 L) and 20 mA corresponds to a full tank (1000 L). The PLC analog input module is configured for 0-20 mA. If the PLC reads a raw value of 5000 (out of a 0-10000 range for the input), what is the actual tank level in litres?

First, calculate the current corresponding to the raw PLC value. A raw value of 5000 out of 10000 in a 0-20 mA range corresponds to 10 mA. Then, scale the 4-20

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Question: An electrician is commissioning a new level control system. The ultrasonic level sensor provides a 4-20 mA output, where 4 mA corresponds to an empty tank (0 L) and 20 mA corresponds to a full tank (1000 L). The PLC analog input module is configured for 0-20 mA. If the PLC reads a raw value of 5000 (out of a 0-10000 range for the input), what is the actual tank level in litres?

Answer options:

  • 250 L ✅ 375 L
  • 500 L
  • 625 L

Correct answer: 375 L

Explanation: First, calculate the current corresponding to the raw PLC value. A raw value of 5000 out of 10000 in a 0-20 mA range corresponds to 10 mA. Then, scale the 4-20 mA sensor output: (10 mA - 4 mA) / (20 mA - 4 mA) = 6 mA / 16 mA = 0.375. Multiply this by the full scale range: 0.375 * 1000 L = 375 L.

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