The TQ402 111-402-000-012 is an eddy current proximity sensor used in VM600 machinery protection and condition monitoring systems. It measures shaft displacement, axial position, radial vibration, and eccentricity without touching the rotating surface. Because it is non-contact, it does not wear down like a contacting tip and works reliably in oily or dirty turbine and compressor environments.
But in industrial practice, most measurement errors do not come from the sensor alone. They come from incorrect gap setting, mismatched extension cables, surface finish issues, or signal conditioner scaling. This guide covers the specifications, model code, installation checks, and accuracy factors that matter when you select, replace, or troubleshoot the TQ402 111-402-000-012.
What the TQ402 111-402-000-012 Measures
The probe generates a magnetic field from its tip. When this field interacts with a conductive target, the signal conditioner converts the distance change into a scaled voltage output. In VM600 installations, the TQ402 is typically connected through an EA402 extension cable to an IQS450 or IPC704 conditioner. That signal then goes to an IOC4T input card, MPC4 protection card, or CPUM rack controller.
Typical applications:
Shaft radial vibration on turbines, compressors, pumps, gearboxes
Axial thrust position monitoring
Rotor speed and keyphasor reference
Eccentricity and slow-roll measurement
TQ402 111-402-000-012 Standard Specifications
The following values are typical for the TQ402 111-402-000-012 when used with a matched VM600 signal conditioner. Always check the serial-specific datasheet if available because cable length and suffix can affect system calibration.
Parameter | Typical specification |
|---|
Sensor type | Eddy current proximity probe |
Tip diameter | 8 mm |
Thread | M12 × 1 |
Linear measuring range | 0–2 mm (0–80 mil) |
System sensitivity | 8 mV/µm (8 V/mm) with IQS450/IPC704 |
Frequency response | DC to 10 kHz (-3 dB) |
Probe/cable temperature | -35 °C to +125 °C |
Connection | Integral cable terminated for EA402 extension |
Target material | Ferromagnetic steel, typically AISI 4140 or equivalent |
Note: frequency response and temperature limits may change with cable length and conditioner type. Do not use the sensor beyond the rated gap range when monitoring critical machinery.
How to Read the -012 Suffix
The TQ402 family uses suffix codes to identify cable length, connector style, and body configuration. The -012 and -013 versions are frequently mistaken for each other because they share the same probe body.
Before replacement, check:
Integral cable length and armor
Connector type at the EA402 junction
Thread length and wrench flats
Serial number label on the cable or connector
A -012 sensor should not be interchanged with a -013 sensor without confirming the loop configuration. If the extension cable length or conditioner channel is set for one suffix, the gap voltage and scaling can shift.
Accuracy Factors That Matter in the Field
1. Target material and surface condition
Eddy current sensors respond differently to different metals. The standard calibration assumes a ferromagnetic steel target such as AISI 4140. If the shaft material is different or has heavy plating, the sensitivity may shift. Surface roughness, scratches, residual magnetism, and runout also create false vibration signals or baseline noise.
2. Gap setting
Set the probe gap at the middle of the linear range, not at the extreme ends. Measure the conditioner output voltage or gap voltage during installation. If the gap is too close, thermal growth may push the target into the probe. If too far, the output may fall out of the linear range and trip falsely.
3. Cable routing and extension matching
The TQ402 signal is small and sensitive to cable capacitance. Use the EA402 extension cable without cutting or splicing. Route the cable away from high-voltage drives, motor cables, and inverter outputs. Shield continuity must be kept intact from probe to conditioner.
4. Temperature drift
All eddy current probes have some temperature coefficient. High-temperature areas near steam turbine bearings can cause drift if the cable is aged or the connector is contaminated. If you detect slow gap voltage change without mechanical movement, inspect the cable and connector, not just the probe.
5. Signal conditioner scaling
The final system accuracy depends on the IQS450 204-450-000-001 or IPC704 244-704-000-042 configuration. The conditioner must be set to the correct sensitivity, measuring range, and channel type. A wrong configuration can make a healthy sensor look inaccurate.
Installation Checklist for Reliable Measurement
Confirm part number TQ402 111-402-000-012 before mounting.
Use a clean, flat, conductive target area at least twice the probe tip diameter.
Set the gap to mid-range and record the initial gap voltage.
Tighten the M12 × 1 thread to the recommended torque. Do not over-tighten.
Keep the probe cable and EA402 extension away from power and drive cables.
Do not bend the cable sharply near the connector.
Verify system output with a calibrator such as 204-215-000-101 before returning to service.
Common Problems and What to Check
Symptom | Likely cause | Action |
|---|
Gap voltage drifts slowly | Connector contamination, cable aging, temperature | Clean connectors, check EA402 shield, replace if needed |
Noisy signal | Cable routing too close to drive/power lines | Reroute cable, check grounding |
Low or no gap voltage | Wrong gap distance, damaged cable, conditioner config | Re-gap, test cable continuity, check IQS450/IPC704 |
False vibration alarms | Surface runout, shaft magnetism, electrical noise | Verify target surface, check runout, reroute cable |
Replacement and Sourcing Considerations
When replacing a TQ402 111-402-000-012, do not select a probe only by “TQ402.” Confirm the complete model code and compare it with the installed sensor. The matched extension cable EA402 913-402-000-012/013 and conditioner channel must be compatible.
At Joyoung International Trading Co., Limited, we supply TQ402 series probes, EA402 extension cables, IQS450 signal conditioners, IPC704 modules, and related VM600 rack cards such as CPUM, MPC4, and IOC4T. We support industrial customers with model matching, technical consultation, and fast delivery to reduce downtime.
If you need a TQ402 111-402-000-012 replacement or a complete sensor-to-controller loop, contact:
You can also check our Proximity Probe inventory or Vibration Monitoring parts for compatible spare parts.
FAQ
What is the difference between TQ402 111-402-000-012 and TQ402 111-402-000-013?
The suffix generally changes cable length, armor, or connector type. Always verify the exact difference with the serial number or manufacturer code before installation.
Can I use the TQ402 with any signal conditioner?
No. For VM600 loops, use the matched IQS450 or IPC704. Other conditioners may not provide the required sensitivity scaling and may not match the EA402 extension cable impedance.
How often should the TQ402 be calibrated?
Calibration frequency depends on the application and plant standard. For critical turbomachinery, many plants verify the complete loop with a calibrator during planned shutdowns or when drift or fault codes appear.
What gap should I set for the TQ402?
Set the gap at roughly the middle of the 0–2 mm linear range to allow shaft movement in both directions. The exact voltage depends on the conditioner configuration, so always use live output monitoring during installation.
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