WM 901 is a digital instrument based on microprocessors designed for controlling refrigeration systems. In particular, it is suitable for application on low or normal temperature “static” systems. The “A” version also includes an alarm relay and the “B” version an internal buzzer which signal an alarm status. The silencing of the buzzer or the change of the relay status can be carried out by pushing any of the buttons on the face plate. WM 901 is suitable for several applications, in range between –50°C and 50°C, and it is available in a 80x123 wall mounted format.