1. ÅSTRÖM, K.J., and HÄGGLUND, T.: ‘Method and an apparatus in tuning a PID regulator’, (US Patent No. 4549123)
2. Process identifier and its application to industrial control
3. GOODWIN, G., and CRISTAFULLI, S.: (CICS Automation Rept No. 96009 and Pro. Patent Application)University of Newcastle, NSW, Australia
4. LUO, R.S., QIN, J., and CHEN, D.: A new approach to closed loop autotuning for PID controllers, (Proceedings of the American Control Conference, Philadelphia, Pennsylvania, June 1998