E1001 “Analog Output Overrange” Fault – Causes and Troubleshooting Guide
1. Fault Description
When the E+H FMU90 ultrasonic level transmitter displays the alarm:
E1001: Analog Output 01 Overrange
it indicates that the first 4–20mA analog output channel has exceeded the normal operating range (below 4mA or above 20mA).
This alarm is typically related to:
- Process level exceeding measuring range
- Electrical issues in the 4–20mA loop
- Incorrect parameter configuration
- Hardware failure of the output module
2. Step-by-Step Troubleshooting
2.1 Verify Actual Process Level (Most Important First Step)
Check the real-time level displayed on the FMU90:
- If the actual level exceeds the configured full scale → output current will exceed 20mA
- If the level is below zero point or echo is lost → output may drop below 4mA
Actions:
- Confirm tank operating conditions
- Adjust measuring range settings if necessary
- Check the ultrasonic probe for fouling, buildup, or signal obstruction
- Perform sensor cleaning or recalibration if needed
2.2 Check the 4–20mA Output Wiring Loop
Disconnect the AO1 terminals and measure the output current using a multimeter.
(1) Open Circuit
- Loose terminal connection or broken cable
- No proper load connected
Result: Output drops below 4mA → triggers fault
Solution:
- Tighten terminal connections
- Inspect wiring continuity
- Check DCS/PLC input module terminals
(2) Short Circuit
- Positive and negative wires shorted
- Cable insulation damage or grounding fault
Result: Output rises above 20mA
Solution:
- Isolate cable sections step by step
- Identify and repair damaged wiring
(3) Reverse Polarity
- Signal wires connected in reverse (+ / – swapped)
Solution:
- Correct AO1 polarity wiring
2.3 Verify Loop Load Resistance
The FMU90 4–20mA output loop has a maximum load capacity of:
≤ 500 Ω
If the total resistance (including DCS input card + cable resistance) is too high, the output current may become unstable or out of range.
Solution:
- Measure total loop resistance
- Reduce cable length or use a lower impedance input module
2.4 Check Instrument Configuration Parameters
Access the FMU90 configuration menu and verify AO1 settings:
Key points to check:
- Measuring range (LRV / URV) matches actual process conditions
- Scaling parameters are correctly configured
- Output failure mode (e.g. 3.8 mA or 22 mA) is properly set
- Unit conversion or offset settings are correct
Solution:
- Restore default scaling if necessary
- Recalibrate zero and span values
2.5 Hardware Diagnosis
If the alarm persists after disconnecting all external wiring:
- Alarm still active → AO1 output module hardware failure
- Alarm disappears → issue is in external wiring or PLC/DCS input card
Also verify:
- Power supply stability (24V DC recommended range: 20–28V DC)
- Power ripple or instability that may affect output circuit performance
3. Quick Field Troubleshooting Checklist
- Confirm whether process level is truly over range
- Inspect AO1 terminal wiring for looseness or short circuit
- Measure actual 4–20mA output with a multimeter
- Verify scaling and configuration parameters
- Isolate external loop to determine internal or external fault
4. Summary
The E1001 Analog Output Overrange alarm in FMU90 is primarily caused by issues in the signal chain rather than instrument failure.
In most real-world cases, the root causes are:
- Wiring faults (open circuit / short circuit)
- Incorrect range configuration
- Excessive loop load resistance
Actual hardware failure of the output module is relatively rare and should be diagnosed only after all external factors are eliminated.