|Sheffield Measurement Head|
Older Sheffield testers had three tubes for the different recommended ranges:
+ Tube #2 (SU) 56 - 170
+ Tube #3 (SU) 0 - 56
Modern Sheffield testers just provide a digital display of the current Sheffield roughness measurement.
In the Summary, the Test Method states: "The effective measuring range of this method is from 0 to approximately 445 Sheffield units." In the description of the Apparatus, the method defines "An air flowmeter, having the capability to measure the range of flow required for the samples to be tested. A range of 0 to 3400 mL/min (0-400 SU) is recommended."
Generally speaking, most modern instruments will display a value with the wording "out of range" or a flashing display if the values are above 400 or 420 SU.