Z620-581 Advanced thermistor design The Ziton Z620 series of heat detectors are based on advanced thermistor technology and provide a reliable response to fires in areas where environmental conditions prohibit the use of smoke detection.The Ziton Z620-581 is a fixed temperature model, operating at 58ºC. It is intended for applications where fluctuations of ambient temperature may be expected for example, over machinery in laundries, or factory locations where industrial processes may cause sharp temperature increases.