HMT-MS – Edge Measurement vs Triangular Measurement
| Edge Measurement | Triangular Measurement |
|---|---|
| Measurement Uses an “edge-through” laser and digital CCD receiver. | Measurement Uses a light source projected on the top of the surface and received by an analog PSD receiver. |
| Surface Measurement is not effected by surface colour or reflectiveness. | Surface Measurement is effected by reflective surfaces effecting both calibration & measurement; reference cylinders must be of a consistent colour to the tested samples. |
| Dirty Lenses Not affected by a dirty lens unless particles are greater than 1mm. | Dirty Lenses Sensitive to particles on the lens and effected by particles smaller than 1mm. |
| Accuracy with Temperature Change < ±0.1mm for ±10 degrees C, tested over ranges from 10 to 30 degrees | Accuracy with Temperature Change ±0.2mm for ±10 degrees C, excluding the effect of the analog to digital converter unit. |
| Sensor Distance The distance of measured object to sensor is 500mm, the distance between sender and receiver is less than 500mm, therefore sender and receiver can both be 250mm from the sample. | Sensor Distance 20mm range and a stand off distance of 65mm to capture the received signal. It is not possible to measure the diameter at 90 degrees and have enough gap between the sensors – therefore the sensors are angled at 120 degrees. Typically Standards specify measurement at 90 degrees; therefore it is necessary to get special dispensation if 120 degrees is used. |
| Calibration Can be done using push button or PC instruction. | Calibration Requires manual intervention and movement of pots |
| Surface Texture Not affected by craters on the surface of the sample, the colour or reflectivity of the light source | Surface Texture The received light source data is effected by craters, colour or reflectivity of the sample surface. |