Co-Presented by: Clay Hile, Parameter Generation & Control, Inc and Al Simpson, SDL Atlas

The spectrometer and its associated software are the key elements in digital color communication. This technology has allowed companies around the world to design, specify, and produce in a repeatable manner to the same set of standards.

An issue that is often neglected is that certain dyes shift in their color characteristics at different temperatures and moisture contents. A sample read in a New York laboratory at 21°C and 40% RH will show different color characteristics than the same sample being measured on a production floor in India at 28°C and 80% RH. To obtain accurate color measurement data, conditioning samples to a specified temperature and moisture content is critical.

To provide a standard condition for textile conditioning at 21.1°C and 65% RH, attention must be giving to the following three areas:

  • Control Constancy – The ability of the conditioner and controller to maintain a constant control at the control sensor location
  • Uniformity – stratification throughout the conditioned space caused by insufficient air flow, heat or moisture loads within the space, or leakage to or from an adjacent space
  • Sensor Accuracy – calibration uncertainty of both the temperature and relative humidity sensors
  • Conditioning Time – the amount of time a sample takes to come to equilibrium at the specified condition.

For example, consider a targeted condition of 21°C ±2°/65% RH ±5% where the display or recording device may indicate a relative humidity control of +2%. Instead of being well within the required specification, it is quite possible that the requirement is not being met when the uniformity and sensor accuracy factors are included with the control constancy. A more comprehensive determination of test conditions can be achieved by considering the following:

  • The best solid-state relative humidity sensors on the market today have an accuracy of +1% (when properly calibrated). In most cases, ±2% is more realistic.
  • Depending on airflow and heat load location within a room, a relative humidity gradient of +1% to +6% could be expected.
  • Add the above to the previously indicated control cycle (±2%) and the net total uncertainty, at any location a test is being performed could be anywhere from +4% to +9% or more.

To obtain the true required conditions, a chamber or room must be designed with all three aspects of condition deviation in mind.