If you are sourcing a proximity transducer for a VM600 vibration monitoring loop, TQ412 111-412-000-012 and TQ402 111-402-000-012 look very close. They are not interchangeable in most loops. The main difference is in probe tip diameter and linear measuring range.
What TQ402 and TQ412 Do
Both are eddy current proximity transducers. They measure shaft relative displacement, radial vibration, axial thrust position, and speed/phase reference on rotating machinery.
They do not work alone. Each transducer must connect to a signal conditioner such as IQS450 or IPC704. The conditioner converts the changing gap voltage into a usable vibration or displacement signal before the VM600 rack processes it.
Raw output from both transducer types is a negative DC voltage proportional to the gap between probe tip and target surface. The difference is how much gap they can cover accurately.
Quick Model Code Read
The two part numbers share the same base structure. In practical sourcing:
- TQ402 = 8 mm probe tip, 2 mm nominal linear range
- TQ412 = 12 mm probe tip, 4 mm nominal linear range
The suffix 111-402-000-012 and 111-412-000-012 carries factory-defined cable length, connector type, and target material code. Always match the complete part number, not only the TQ402 or TQ412 prefix.
The 402 and 412 segments are the critical functional differentiator. The 000-012 suffix may be identical or different, but it is not safe to assume interchangeability.
Key Differences
| Parameter | TQ402 111-402-000-012 | TQ412 111-412-000-012 |
|---|---|---|
| Probe tip diameter | 8 mm | 12 mm |
| Nominal linear range | 2 mm | 4 mm |
| Sensitivity | Higher mV/µm | Lower mV/µm |
| Target surface required | Smaller flat area | Larger flat area |
| Typical mounting thread | M10x1 | M14x1.5 or larger, confirm suffix |
| Common use | Radial vibration, speed pickup | Axial thrust, wide displacement |
| Installation space | Smaller footprint | Larger clearance required |
These values are typical for standard VM600 configurations. Exact electrical and mechanical details can vary by suffix and probe calibration. Always confirm against the original manufacturer datasheet for the specific part number.
When to Choose TQ402 111-402-000-012
TQ402 is the right choice when:
- Installation space is tight around the bearing housing
- You are measuring shaft radial vibration on a small to medium machine
- Target area is limited, such as a narrow shaft collar
- You need higher sensitivity for small vibration amplitudes
- The existing VM600 channel is configured for 2 mm range
Typical examples include small pump radial vibration monitoring, motor shaft end reference, and speed/phase pickup where only a small target is available.
The smaller 8 mm tip makes TQ402 easier to fit in compact bearing housings. It gives good resolution for vibration signals where gap change is only a few hundred micrometres.
When to Choose TQ412 111-412-000-012
TQ412 is better when:
- You need to measure axial thrust position or large displacement
- The gap change can exceed 2 mm during startup or thermal expansion
- The target is a large flat thrust collar
- You need a wider linear range without signal saturation
- The installation can accept a larger probe body
Typical examples include steam turbine thrust bearing position, compressor axial displacement, and large gearbox shaft movement.
The 4 mm linear range of TQ412 does not mean better accuracy in all cases. It trades sensitivity for range. For small vibration measurements, TQ402 is usually more appropriate.
Signal Chain and Configuration
Both TQ402 and TQ412 feed into the same VM600 architecture:
Sensor → IQS450 or IPC704 conditioner → IOC4T input card → CPUM processor
However, the channel scaling in the IQS450 or IPC704 must match the transducer range. If you replace TQ402 with TQ412 without re-ranging the signal conditioner, the displayed displacement and vibration values will be wrong. This can trigger false alarms or miss real machine faults.
The probe gap setting also changes. TQ402 is typically set to the middle of a 2 mm range. TQ412 must be gapped to the middle of a 4 mm range. The target surface flatness requirement is also different.
Replacement and Procurement Mistakes
Common mistakes we see in field replacements:
- Matching only TQ402 or TQ412 and ignoring the suffix.
- Assuming TQ402 and TQ412 have the same cable length or connector.
- Replacing one transducer type with the other without updating IQS450 scaling.
- Using a different target material than the original calibration.
- Mixing TQ402 and TQ412 in redundant measurement channels.
- Not re-gapping the probe after installation.
For a like-for-like replacement, always provide the full part number from the existing probe or the original system documentation.
FAQ
Are TQ402 111-402-000-012 and TQ412 111-412-000-012 interchangeable?
No. TQ402 has an 8 mm tip and 2 mm nominal range. TQ412 has a 12 mm tip and 4 mm nominal range. They require different signal conditioner scaling and probe gap settings.
What does the suffix -012 mean?
The suffix normally encodes cable length, connector type, and sometimes target material calibration. The exact meaning is factory-defined. It is not safe to guess from the number alone.
Can I use TQ412 for radial vibration measurement?
It can work in some cases, but TQ402 is generally better for radial vibration because of higher sensitivity. TQ412 is intended for larger displacement or thrust position where a wider gap range is needed.
Which transducer should I use for steam turbine thrust position?
If the expected axial movement can exceed 2 mm, TQ412 with 4 mm range is the safer choice. For standard radial vibration probes, TQ402 is more common.
Can you supply both TQ402 and TQ412 spare parts?
Yes. We stock and source both TQ402 111-402-000-012 and TQ412 111-412-000-012, along with matching IQS450, IPC704, IOC4T, and CPUM modules. Send your full part number for a compatibility check.
Get the Correct Transducer for Your VM600 Loop
Do not replace a proximity transducer based on a partial model number. The difference between TQ402 and TQ412 is not cosmetic. It changes range, sensitivity, gap setting, and channel configuration.
If you are not sure which part number your loop requires, send the full part number and a photo of the existing probe to [email protected] or call/WhatsApp +86-181-5013-7565. We can confirm the correct replacement and current stock availability.
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