Actuators linearization of a large volume environmental simulation chamber via pulse code modulation

Ultra -stable room -sized environmental chambers may involve significant power variations leading to hysteresis and nonlinearities of the stabilization system. This paper describes utilization of a pulse code modulation control which significantly reduces observed nonlinearity of the chamber actuation system. Stability of environmental conditions for temperature Delta T = +/- 25 mK (15-35 C-degrees dynamic range), relative humidity Delta Rh = +/- 0.1% (3%-95% dynamic range), and pressure Delta P = +/- 12 Pa (+/- 500 Pa dynamic range) was achieved within 27 m(3) chamber volume, which is two orders of magnitude better than the corresponding stabilization achievable using a standard linear proportional-integral-derivative (PID) controller. Utilizing this chamber we have demonstrated two orders of magnitude improvement of the operational relative frequency stability of ultrastable quartz oscillators (USO), reaching 2 x 10(-13) stability at 1-10(5) s averaging time.