If I short the two wire, what will happen the loop?

Shorting the two wires in a current loop, such as a 4-20mA loop commonly used in instrumentation, essentially creates a zero-resistance path for the current. This results in bypassing the device that the loop is intended to power or receive a signal from.

Depending on the specific design and safety measures in place, the following could happen:

  1. Loss of Signal: The connected device, such as a transmitter or sensor, will no longer be able to send a meaningful signal to the controller or data acquisition system.
  2. Current Fluctuations: The loop current will no longer be controlled by the device, possibly leading to erratic behavior in the loop.
  3. Potential Damage: If the current source is not designed to handle short-circuits, it might get damaged.
  4. Alarm Trigger: Many modern control systems have built-in protections to detect such conditions, and shorting the wires could trigger an alarm.
  5. False Readings: The controller or data acquisition system might register minimum or zero values, which could lead to incorrect actions being taken by the control system.
  6. Operational Halt: Safety mechanisms may stop operations until the fault is cleared to protect the system and the process.

It’s crucial to address such short-circuits immediately to prevent system malfunctions, potential damage, and ensure operational safety. Always consult device-specific manuals for guidance on how to properly address short-circuits.