Field Voltage Too Low

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The voltage supplied to the power contacts of the terminal is below the permissible operating range (24V -15%/+20%). This can be caused by the voltage not being switched on, being switched on after the terminal supply, being generally too low, or by a short-circuit at an output causing a voltage drop. This affects the overall operation of the terminal's outputs and can lead to unreliable behavior or shutdown of safety functions.

• Degraded or undersized 24VDC power supply unit (PSU) failing under load, resulting in output voltage below 20.4VDC.
• Excessive voltage drop across long field power wiring or undersized conductors, causing terminal voltage to fall below 20.4VDC.
• Tripped circuit breaker or blown fuse on the 24VDC field power supply circuit.
• Faulty power contact terminal block or connection issue preventing full voltage delivery to the module.
• Incorrectly configured power-on sequence where the field voltage is not applied before the terminal initialization.

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1. 1

   1. Using a calibrated multimeter, measure the 24VDC field supply voltage directly at the input terminals of the affected module. Voltage must be within 20.4VDC to 28.8VDC.

2. 2

   2. Measure the output voltage of the 24VDC power supply unit (PSU) at its terminals. If it's consistently below 20.4VDC under normal load, replace the PSU.

3. 3

   3. Inspect and verify the continuity of the fuse or integrity of the circuit breaker protecting the 24VDC field supply circuit. Replace fuse if open or reset breaker.

4. 4

   4. Calculate the voltage drop for the field power wiring based on wire gauge and length; if excessive, install larger gauge wire or a localized power supply.

5. 5

   5. Verify that the field power is enabled and stable for at least 500ms before the control system attempts to initialize the terminal to prevent startup race conditions.