Glossary of Control Engineering Terms - X, Y, Z

Z-Transform: A transform to convert a discrete time differential equation into a transfer function from which system connections can be manipulated easier and frequency responses calculated. Sister of the S-transform.

Zero: A root of the transfer function numerator polynomial. Can be real or complex conjugate. Poles with a negative real part are stable. The poles determine the transient response of the system. Fast poles are much further away from the stability boundary than other poles and the transients associated with these poles will decay faster. Dominant poles are closer to the stability boundary and being slow will dominate the transient response.

Zero-order Hold: A sampled signal is converted to analogue form by 'holding' the most recent value.

Ziegler Nichols PID Tuning: A semi-empirical PID tuning method based around a step response obtained experimentally.