When designing a non-contact, inline laser thickness monitoring system, the simplest approach may seem like the best. Mount a pair of sensors on your line, and you're done, right? Not so fast. While this solution appears straightforward, the reality of precision measurement is more complex.
The Unpredictable Nature of Temperature
The reality of manufacturing facilities is that the ambient temperature fluctuates. Temperatures change daily and seasonally due to factors like the climate and nearby equipment. These variations can significantly impact measurement device accuracy.
The Reality of Laser Sensor Drift
Laser sensors, even high-end models, are susceptible to drift. Temperature changes cause mechanical expansion of sensor components and impact sensor electronics. This drift is documented in sensor datasheets as a specification of drift per degree of temperature change.
The Magnitude of the Problem
- High-end triangulation sensors commonly experience thermal drift of 0.01% of full scale per degree Celsius.
- For a sensor with a working range of 20 mm, that translates to an error 2 µm for every °C.
- A 10°C temperature swing can result in a 20 µm shift if left uncorrected.
Frame Expansion: The Overlooked Factor
Even the frame holding the sensors can contribute to measurement error. An aluminum C-frame with a 10-inch vertical arm will drift by 6 µm for every 1°C change.
The Total System Error
A typical system with two laser sensors and an aluminum C-frame has a combined error of 10 µm/°C. A daily temperature variation of 10°C introduces 100 µm of error. A seasonal variation of 20°C introduces a staggering 200 µm of error.
The Invisible Threat
The most insidious aspect of thermal drift is its invisibility. The laser-thickness reading may appear accurate, leading to a false sense of confidence while the process continues with significant errors.
Mate Gauge Solution
Mate Gauge scanning systems overcome temperature-drift errors with a motion system that moves the C-frame, allowing for automatic re-zeroing against a reference standard. This effectively eliminates the effects of temperature and thermal drift.
Key Takeaway
Ignoring temperature effects in non-contact laser thickness measurement can be costly. The seemingly simple solution of mounting sensors can lead to significant errors. Mate Gauge scanning systems are immune to temperature drifts and provide the accuracy and reliability needed for high-precision thickness measurement in industrial manufacturing environments.